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Halovinylene Carbonates in Organic Synthesis. New synthetic methods (2)

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[ 3 3 ] R. S. Asqrrirh and U. c'. Purkii7.soii, Text. Res J. 34. 1064 (1966).
[34] J . Bjurnuson and K . J. Carprntrr, Brit. J Nutr. 23, 859 (1969).
[35] J . Bjurnuson and K . J. Curpmtrr, Brit J. Nutr. 24, 3 I3 ( I 970).
[36] L. Lorund. K . K o n u h i , and A. Jambsen, Nature 194. 1148 (1962)
[37] L. Lorund, H H . Ong, B. Lipinski, N . G. Rtrlr, J . Doisnry, and A .
Jucohsm, Biochem. Biophys. Res. Commun. 25, 629 (1966).
(381 G. A4. Fnllrr and R. F. Dooiirrk, Biochem. Biophys. Res. C'ommun.
ZS, 694 ( 1966).
[39] S. Murucice and A. G. Luewj., Biochem. Biophys. Res. Commun. 30,
356 (1968).
[40] J. J. Pisunu, J. S. Finiqaon, and M. P. Perton, Science 160, 892 (1968).
[41] L. Lorund, J . Downer, T Goron, A . Jucobsen, and S . Tokirru, Biochem.
Biophys. Res. Cornmun. 31, 22 (1968).
[42] J . C . Flrtchrr, personal communication (Jan 1969).
[43] M . Cok, J. C. F/@rcher, K . L. Gurdiirr, and M . C. Cor;fir/d, Appl.
Polym. Symp. 18, 147 (1971).
[46] B Milligun, L. A. Holr. and J . B. Culdx.r/l, Appl. Polym. Symp. 18.
113 (1971).
[47] H W H . Hurding and G. E . Rodgrrs. Biochim. Biophys. Acta 2.57,
37 i1972).
[4X] A . G. L o e w , S. S. Motucis, and M . S h o w , Fed Proc. 30 (Part 2),
1299(1971).
[49] R. S Asqrrith and M. S. Otterburn, Appl. Polym. Symp. 18, 277 (1971).
[50] M. S. Orrerhrrm, Ph. D Thesis, University of Bradford (England) 1970.
[51] H . Zuhn, Palette 42, 29 (1973)
[52] R. S. Asquirh. M . S . Oti~~rhnrn,
and J . A . Swift. J. Text. Inst. 63. 544
( 19721.
[53] K . J. Curpmtrr. Nutr. Soc. Eng. and Scot. 17, 91 (1958).
[54] C. H . Leu and R. S. Hunnuh, Biochim. Biophys. Acta 4, 1950 (1950).
[ 5 5 ] K . M. H m r j . and S. K . Koii, Biochim. Biophys. Acta 5, 455 (1950).
[56] R. S. Asyirirh and M . S. Otterburn. J. Text. Inst. 60, 208 (1969).
(441 R. S . Asqirirh, M . S. Orrerbirrn, J . H . Blrchunuu. M . Cole, J . C F/rtc.hw,
and K L. Gurdnrr, Biochim. Biophys. Acta 207, 342 (1970).
[57] P. E. Wuiblr and K . J.,Carprntrr, Brit J. Nutr. '7. 509 (1972).
[45] R. S. Asyirirh. M . S. Orrerbrrrn, and K . L. Gurdnrr, Experientia 27,
1388 (1971).
[58] R. S. Asqarrh, M . S. OcsLvb[rrn.M.: J. Sudui?, K . J. Curpmter, and
R. Hwrel, unpublished results.
F
.
,
Halovinylene Carbonates in Organic Synthesis
New synthetic
By Hans-Dieter S t h a r f [ * l
Monohalo- and dihalovinylene carbonates constitute a new class of cyclophiles which permit
simultaneous introduction of masked 2-hydroxyketo and cr-diketo functions, respectively, into
the cycloadducts. Demasking can be performed by simple hydrolysis. Solvolytic opening of
the carbonate ring leads to glycolic acid derivatives in the case of the monohalo compounds
and to glyoxylic acid derivatives with the dihalo compounds. Preparation of the title compounds,
their potential as synthetic reagents, and the chemistry of their simple reaction products are
surveyed from a preparative viewpoint.
1. Introduction
Formal replacement of two hydrogen atoms of glycolaldehyde
by halogen X raises the oxidation states of the two C atoms
Vinylene carbonate (1,3-dioxol-2-one) ( I ) , the parent compound of the class, has been known since 1953['], and its
behavior as a reactant in both thermal'' 91and photochemical
cyc10additions~~~' has been repeatedly investigated.
0;;
H+OH
{I), X
(21, x
(3j. X
(4), x
(s). x
=
X'= H
=
x' = c1
uic-cis-gl ykols
= R r , X' = H
=
=
1
H
glycolaldehyde
c1, x' = II
X' = Rr
Compound ( I ) is the cyclic carbonate of the cis-enediol form
of glycolaldehyde. The oxidation states of the two carbon
atoms, which differ in the reductone form of glycolaldehyde' 61
( + 1 and - I), become equal in the tautomeric enediol form;
cycloaddition to an rn-centered n-electron system yields an
adduct exhibiting the oxidation pattern of a vicinal cis-diol.
a-diketones
glyoxylic acid
derivatives
\OH
x-hydroxyketones
glycolic acid
derivatives
[*] Prof. Dr. H.-D Scharf
lnstitut fur Organische Chemie
51 Adchen, Prof.-Pirlet-Strasse I (Germany)
520
H'
enediol form
Angew. Chrm. inrrmut. Edit.
reductone
form
1 Vol. 13 ( 1 9 7 4 ) 1 No. 8
by two, both in the reductone form and in the enediol form.
Cycloaddition reactions then furnish adducts having the oxidation pattern of an a-diketone. These compounds can be liberated by solvolysis.
Finally, a tautomeric enediol form is also conceivable for
corresponding derivatives of glycolic acid with differing oxidation states ( + 2 and 0) at the two centers, which-being fixed
by the carbonate ring as in the other cases--confer the oxidation pattern of a n a-hydroxy ketone upon the cycloadduct.
This formalism provides a satisfactory description of the
chemistry of the vinylene carbonates ( 1 )-(5). Two-center
attack at positions 4 and 5 in ( l ) - ( 5 ) leads to derivatives
of the enediol form, while nucleophilic attack at position
2 affords derivatives of the reductone form["].
Hence vinylene carbonates are versatile reagents for the preparation sf substances which are accessible only with difficulty,
if at all, by other routes.
The present progress report surveys the (mainly preparative)
results obtained so far with the derivatives ( 2 ) - ( 5 ) .
2.1. Dichlorovinylene Carbonate (2)
The first representative of the halovinylene carbonates (2)
was prepared from ethylene carbonate (6)" ',I s ] . Photochlorination of (6) according to Ellingboe and Melby"'] leads
riu compounds ( 7 ) - ( 9 ) to tetrachloroethylene carbonate
( 1 0 ) (820/0), which affords dichlorovinylene carbonate (2)
(85 YO)
on treatment with Zn(Cu) in ether.
The lacrimatory liquid solidifies to crystals (m. p. 19 C) below
room temperature and can then be stored indefinitely in a
refrigerator.
In the liquid state and in dilute aprotic solvents, CO is eliminated to form increasing amounts of oxalyl chloride" *I,
a fact which has led to erroneous interpretation of UV absorption measurements, especially in the presence of
(see Section 7). The lattice energy apparently contributes to
stabilization of the molecule. Experience has shown that small
amounts of oxalyl chloride d o not interfere in preparative
~
[*] T h e numbering of the ring atoms is based upon that of the 1,3-d1oxole
system.
1 Yo/. 13
(1974)
In the presence of triphenylphosphane or trimethyl phosphite,
however, (2) undergoes spontaneousdecomposition with elimination of CO at room temperature"']. This reaction, whose
mechanism has not yet been elucidated, is typical of the halovinylene carbonates ( 2 ) - ( 5 ) : it IS not observed with the
parent compound ( I ) or its dialkyl derivative" 31 ( X =alkyl).
Moreover, it is remarkable that tertiary amines do not induce
cleavage.
In how far the purely thermal elimination of CO to form
oxalyl chloride can be classified as a cheletropic cleavage
has been investigated in a theoretical study[2''.
2. Preparation and Properties
Angrw. ('hem. inrernui. Edit.
reactions. Even at elevated temperatures (b. p. 143"C/760 torr)
the half-life for cleavage is large compared to the reaction time.
No. N
2.2. Monobrornovinylene, Monochlorovinylene, and Dibrornovinylene Carbonate ( 3 ) , ( 4 ) , and (5)
Exhaustive free-radical bromination of ethylene carbonatc (6)
in analogy to the chlorination does not lead to a preparatively
useful result in the intended sense. Halogen-exchange reactions
with compounds ( 8 ) and ( 1 0 ) also prove unsuitable as a
method of preparing the homologous halo derivatives (3)
and ( 5 ) . Nor can monochlorovinylene carbonate ( 4 ) be
obtained from ( 8 ) by elimination of HCI under S,2 conditions,
a result which confirms the frum positions of the CI atoms
in (8)["'. In contrast, dibromoethylene carbonate ( 1 1 ),
obtained by addition of bromine to ( 1 ), eliminates HBr to
form (3)[231.Thus ( 3 ) became the key substance for preparation of ( 4 ) and (5)[241.
Addition of chlorine to ( 3 ) affords monobromodichloroethylene carbonate (!2), which isconverted into ( 4 ) on treatment
521
with zinc in ether'"]. Furthermore. 1 3 ) can be transformed
into tribromoethylene carbonate (13) which yields dibroniovinylenc corbonatc ( 5 ) o n HBr elimination.
Attempts t o prepare diiodovinylene carbonate ( 1 1. X = X ' = 1.
by a Finkelstein reaction failed t o give any isolable product
apart'from elemental iodine and CO.
3. Solvolysis Reactions
3.1. Dihalovinylene Carbonates
I
Methanolysis and aminolysis of (-7) lead to derivatives of
glyoxylic acid. The former reaction initially affords methyl
0-methoxycarboiiylchloroglycolate ( 14 ), and the latter the
corresponding anilide ( i 5 ) l ' x 1 .
4. [4 + 21-Cycloadditions
4.1. Preparative Results
Diels-Alder reaction of ( 2 ) with a series of l,.?-dienes furnishes
[4 + 21-cycloadducts, some of which are obtained predominantly in the LJSO form.
J
Methanolysis of ( 2 ) under reflux or methanolysis of (14)
under more drastic conditions finally affords the dimethyl
acetal ( 1 6 ) of methyl glyoxylate.
0
3.2. Monohalovinylene Carbonates
There are fundamentally two different reaction routes open
t o solvolysis of the monohalo derivatives ( 3 ) and ( 4 ), depending upon whether the nucleophile initially cleaves bond A
or B. Rupture of bond A would lead to a derivative of r-haloglycolaldehyde ( / 7 ) . whereas cleavage of bond B would yield
a glycolic acid derivative.
Both alcoholysis and aminolysis give only products arising
rirr route BI'']. Treatment with methanol yields methyl 0methoxycarbonylglycolate 118 ), and aniline forms the anilide
(19).
Table I I'roduct and iro:tclion dnta lor [ 4 + 7]-c).cloaddt~ioi~\
w i t h 12) or (3).
.
C'onipoiicnts
522
T[
('1 [d]
Products, overall yield
[',I
Stereoisomers. rn p. ['C]
Anyeu, Chrm. internal. Edit.
I Vol. I3 I I Y 7 4 ) /
NO. N
While cyclopentadiene ( 2 0 ) and 1,3-cyclohexadiene ( 2 1 ) give
exclusively the corresponding endo adducts, ( 2 3 ) and ( 2 4 )
respectively[2’! furan ( 2 2 ) is found to give the two stereoisomeric adducts in the ratio ( 2 5 ) : ( 2 6 ) = I :2, together with
small amounts (1.5%) of a 2 : 1 adduct (27)L2h1.In contrast
to the adduct of furan and maleic
or maleimideL3*1.attempts at subsequent mutual interconversion of
adducts (-75) and (26) at the temperature of formation or
above prove unsuccessful, thus justifying the assumption that
the YZO form (26) arises on an energetically competitive reaction coordinate with YO regioselectivity.
dichloromaleic anhydride 140)---towards 9,lO-dimethylanthracene (33J. the activation parameters of the reactions were
measured (or taken from the Iiterat~re’”~)
(see Table 2).
/fT/
( I ) , 17). i.19) (40)
Table 2 Kinetic data for the reactk
VI ( I / . [34] for f3YI ( 3 3 ) . L r refers t o
-.-
Dienophile
f3Y
/40)
(2)
(/I
X
X’
Z
)H
CI
“1
CO
CO
0
0
0
0
(‘0
H
c‘o
IO’LZ
[lmol’>’
14100
145
8.7
14
With cycloheptatriene, the three adducts (2Y)--(3/) are
formed. Here too, YNO preference is observed in contrast to
the cycloheptatriene/maleic anhydride adducts[”’l which are
formed in a ratio of 84: 15: 1 at 176 C. The structures are
analogous to those of (29)---(31). Table 1 lists the data
for the Diels-Alder adducts formed with (2).
Anthracene ( 3 2 ) and its 9,lO-dimethyl derivative (33) are
also suitable as dienes for Diels-Alder reaction with (2)12’I.
1:
10.9
I3 I + 0 4
17.2 kO.3
22 i 1.3
10 2
- 13
124t04
16.1tO.7
? I . i i l3
- 37
- 32
10071
I04
0.2
- 2.3
In the case of the maleic acid derivatives (3Y) and ( 4 0 ) .
chlorine substitution at the double bond of the dienophile
raises the activation barrier of the reaction with (331, while
in the carbonate series reaction with the dichloro compound
( 2 ) proceeds slightly more readily than with the parent compound ( I ) . The activation entropies found for reactions with
(39). 140). and ( 2 ) are normal, in agreement with literature
while the reaction with ( 1 ) displays a surprisingly
low value[”’]].
Assuming that the magnitude of the frontier orbital interaction
between the reactants at the start of reaction plays a dominant
role in controlling the height of the activation barrier~’”..’~J
enables us to reach a qualitative understanding of the differing
effects ofchlorine substitution in the two classes of compounds.
171
I
-14
-it
.
b2
ill
b2
Under the usual conditions, ( 2 ) fails to react with open-chain
Fig. I. C’omparison of [4x.+ 2x.]-cycloadditions with “normal” a n d with
I ,3-dienes such as butadiene and isoprene. However, a I5 %
“inverse” electron demands. T h e plot shows the E H T M O cncrgies [39]
yield of the adduct (37) is formed with 2,3-dimethylbutadiene
calculated for compounds ( I ). ( 2 1 . f331. / ~ Y I and
.
(401. Scc text for d c t a ~ l s .
Monobromovinylene carbonate ( 3 ) likewise affords
a Diels-Alder adduct (38) (22% yield) with ~ y c l o p e n t a d i e n e [ ~ ~ ~
The calculated[”y1orbital energies of the reactants are plotted
(Table 1).
in Figure I . The symmetry-correct interactions of the HOMO
of (33) with the pertinent LUMO of ( 3 9 ) and (401, which
4.2. Kinetic Resultd3’. 331
lead to an energy-lowering splitting along the reaction coorI n order to compare the dienophilic activity of the vinylene
dinate, show that owing to the greater energy difference in
the case of ( 4 0 ) the activation energy of this reaction will
carbonates ( I ) and ( 2 ) with those of the corresponding combe higher than in the case of (3Y).
pounds of the maleic acid series-maleic anhydride (3Y) and
Anyrw. Chrm i n r r m a t . Edit.
Vul. 13 ( 1 9 7 4 )
1 Nu. 8
523
Since both dienophiles are “electron deficient”, i. e. possess
high ionization energies, whereas the diene (33) is “electron
rich”, these reactions are classified as “normal” Diels-Alder
reactions[‘”! A different situation is encountered with compounds ( f ) and (2). Here a symmetry-correct interaction
can only occur between the respective H O M O of ( 1 ) and
(-7) and the L U M O of (33), in such a manner that a higher
activation barrier is to be expected in the reaction with ( l )
because of the greater difference in energy. Owing to the
direction of electronic polarization, these reactions are said
to belong to Diels-Alder reactions having “inverse” electron
demandsl“-“’ll 1
Application of second order perturbation theoryf38.I’‘ also
permits rationalization of the regioseIectivity of the {4 + 21-cycloaddition of (2) to furan and estimation ofthe exo preference.
For this purpose the EHT MO energies[391and the corresponding LCAO MO coefficients are shown in Figure 2 for the
energy levels of furan and the cyclophile ( 2 ) which are relevant
in a zero-order approximation.
a1
furan
If it is assumed, in keeping with second-order perturbation
theory for cycloaddition with simultaneous bond formation
between two or more reaction centers of the reactants[431,
that the route-determining stabilization component AE of
the rr-electron energy is primarily proportional to the square
of the sum of the coefficient products taken over the interacting
centers of the reactants, and inversely proportional to the
energy gap between the levels considered [HOM0(2) and
LLTMO(furan)], then the exo preference of the reactants can
be explained as follows:
The secondary interaction of the CI atoms of (2) with positions
3 and 4 of furan in the exo arrangement is greater (+0.47)
than the secondary interaction with the oxygen atoms (+0.16)
in the endo orientation.
It thus also becomes understandable why the parent compound (1) adds mainly endo-selectively[2-J.
in
‘
the thermal
[4 2]-cycloadditions known so far.
Considerations of this kind are obviously very crude: they
can claim no more than to indicate general trends. Nevertheless, regioselectivities can be articulated more precisely
in this manner than in terms of the stereochemical rules
derived empirically[44].
’.
+
5. x-Diketones and Simple Derivatives
-
ibzl
LUMO
i’”
0 O-*‘
Ib,l-
\\
LUMo
,
26 - X
Hydrolysis of the [4+ 2]-cycloadducts (23)--(27), (29)( 3 1 ) , (34), and ( 3 5 ) afford bridged r-diketones, some of
which were hitherto unknown. The initial products are condensed hydrate forms from which the r-diketones (41)(47)[Z5.2h1
can be obtained pure by sublimation (Table 3).
\
\
\
0
+W
i 47)
-0.03
HOMO
1.4-exo
[“I
I!.
Cxpcriiiicntal ioniiiitioii energies for ( / ). 10.3. and for ( 2 ) . 9 . 9 2 ~ V .
1, ‘ind K . W i t i d . pcrsonal comniunicatlon
Bin
524
1,G-endo
Hydrolysis of compound (37) expectedly yields 4,5-dimethylpyrocatechol(48), while adducts with monohalovinylene carbonates, e. g. ( 3 8 ) . lead to 3-hydroxy-5-norbornen-2-one
(49)
(Table 3). N o spectroscopic evidence is obtained for the presence of the enediol form in this substance. The monoketals
are readily formed by methanolysis of the cycloadducts in
the presence of hydrogen carbonate. The a-diketones (41 ),
(421, and (44)--(46) are yellow to orange, and the diketones
(43) and (47) are red. This deepening of color is apparently
due to interaction between the oxygen p orbital, which is
symmetrical with respect to the molecular plane, and the
Angcw. Chvm inturnor. Edri
VO/. 13 ( 1 9 7 4 )
/
NO. 8
ketones[5” - 601. On irradiation, the ketals ( 4 1 u ) and ( 4 3 ~ )
are in photochemical equilibrium with the four-membered
cyclic ketals (41 h ) and ( 4 3 h ) respectively. The reacting excited
state is most probably a singlet. Nevertheless, the reaction
$, orbital of the “diene” grouping formed from the two keto
groups positioned cc to each other. Owing to the ensuing
splitting, the energy gap to the lowest unoccupied z* level
IS reduced.
Table 3 r-Diketones and their monodimethyl acetals prepared by hydrolysis and methanolysis. respectwely. of the
adducts (23]---(27).[ 2 9 ] - [ 3 / ~ ,(341. and 135).
~~~~
AdducUs)
~~
.-
~
._
~~
- .-
~~
Dikctone
Yield
M. p.
[
Ref.
[“/,I
(‘I
5.1. Photolytic and Therrnolytic Studies
The r-diketones ( 4 1 ) - ( 4 6 ) and the monoketals ( 4 1 u ) ,
( 4 3 a ) , and ( 4 4 ~ 1 are
) formally Diels-Alder adducts of the
parent dienes with the hitherto unknown “bisketene” CZOZ,
unsuccessfully sought by S t u ~ r d i n g e r [and
~ ~ ~ its
, monoketal
dimethoxyketene (50), respectively. Since both these cyclophik-provided they exist at all-would be antarafacial reactants,preparation oftheabovecycloadducts by [47t, + 2n,] DielsAlder addition is impossible. Once the cycloadducts had
become available by the above route, however, it seemed
obvious to attempt a preparation of the unknown cyclophiles
C,O, and (50) by [47t,t27ta] cycloreversion of the adducts,
which should possess a favorable reaction coordinate when
performed photochemically. Photolysis of the diketones
( 4 1 ) - 4 4 6 ) leads almost completely to the dienes and carbon
monoxide. N o experimental evidence is obtained for the transient occurrence of C 2 0 2 ( 5 1551.
~
Photolysis of the monoketals ( 4 1 ~and
) ~(43a)[’“
~ ~ ~follows
a fairly uniform mechanism resembling that of P,y-unsaturated
Ketal
- .-
~
-
Yield
[“h]
-
B. p
[ C:torr]
does not involve a concerted sigmatropic [1,3], shift; instead,
initial formation ofadiradical intermediatecapable ofa variety
of further reactions has to be assumed on the basis of temperature dependence.
Isomerization of the diradical intermediate to a cyclic oxycarbene (“oxacarbene”) and subsequent addition of methanol
leads to the stereoisomers of compounds ( 5 I ) and (5-71, whose
stereochemistry could be established by NMR spectroscopy
with aid of paramagnetic shift reagents[“. 261.
Decarbonylationoccursonlyfor Z=CH2 to form the dimethyl
ketal of bicyclo[3.1.0]hex-2-en-6-one { 5 3 ) .
When Z = 0,thediradical decomposes to furan and dimethoxyketene (50) which can be trapped as the dimethyl acetal
of the glyoxylic ester ( 1 6 ) with methanol[2h1.This cleavage,
which was formerly observed on photolysis of dehydronorcamphorl”’, does not occur with ( 4 1 0 ) ( Z = C H z ) ,thus also confirming the intermediacy of the diradical whose substituent
effectsdepending upon Z are manifested in the varying cleavage
pattern .
Photolysis of ( M u ) with decarbonylation proceeds in highly
uniform manner, and has been utilized in an elegant synthetic
route to the o-bishomobenzene series, e.g. to (54)Iz6’.This
finding can likewise be rationalized by assuming an intermediate diradical.
The fruns conformation of the two cyclopropane rings follows
compellingly from the stereochemistry of the original monoketal (44a) and is confirmed by ‘H-NMR
These results would indicate that-despite participation of
singlet states--the fragmentation reactions proceed in a stepAngew. Chem. infernat. Edit.
/ Vol. 13
( 1974)
J No. 8
525
wise manner, 1. e. the coordinates of the concerted [ 4 n , + 2 ~ , ]
cycloreversion apparently lie at higher energy than would
correspond to the energy of the light quantum of the incident
radiation. Since the cyclophiles considered are antarafacial
components even higher encrgies are to be expected for
[4n,+ 2n,] cycloreversion. I t is therefore not surprising that
thermolysis is by no means homogeneous but yields a wealth
of fragments whose genetic sequences have not yct been elucidated'h31.The results of thermolysis of compounds ( 4 1 ( I )
and ( 4 1 c ) serve as illustrative examples.
lA
ide (CO),,.dehydration always modifies the molecule["I. However, ( 5 5 ~ which
)
is more readily obtained in crystalline
form, can be converted into an orange cyclobutanetetrone
tris(semicarbaz0ne) monohydrate 158) by treatment with
semicarbazide hydrogen chloride.
OCH3
H 3 C 0 OCH,
o<z#oh
H O P - R
(Yob)
(Ila)
N-R
R-K
H
=
H 3 C 0 OCH,
-NH-CO-XH,
158)
( 3.5
a)
(2.3V")
0
(0.5%)
( J:
"0)
(39)
The chlorine atoms of the isomers ( 5 5 ) undergo extremely
ready nucleophilic replacement prior to solvolytic opening
of the carbonate ring. Dissolution in, P.CJ., methanol leads
very rapidly to a homogeneous tetramethoxy compound ( 5 9 )
of unknown stereochemistry : no intermediates can be detected
by gas chromatography.
(4)
The bis(dimethy1 ketal) ( 4 1 ~ of
) norbornenedione ( 4 / ) can
be formally regarded as the Diels-Alder adduct of tetramethoxyethylene to cyclopentadiene, although it cannot be prepared
from the components'"''. In this case too, the [ 4 n , + 2 ~ , ]
cycloreversion coordinate appears to be energetically very
high. Hence thermolysis of ( 4 1 c) only affords compounds
to be viewed as stabilization products of intermediate radical
fragmentslh51. These adducts ( 4 1 ( I ) and ( 4 1 c ) , which are
obtainable riiu cycloaddition of 1 ..?-dimes to dichlorovinylene
carbonate (2), can therefore be termed "pseudo-Diels-Alder
adducts".
"syn" + "anti"
Irradiation of 1 : 1 mixtures of monochlorovinylene carbonate
( 4 ) and acetone with the aid of a high-pressurc mercury
lamp leads to the formation of four stereoisomeric CJ-cyclodimers ( A ) - ( D ) , one of which [ ( A ) ] is relatively insoluble
and precipitates during irradiationlz4! The stereochemical
details have yet to be elucidated.
Table 4. Physical properties of thc CI-dimers of monochlorovinylene carbonate ( 4 )
..
6. [2+ 21-Cycloadditions
6.1. Photochemical Cyclodimerization of Di- and Monochlorovinylene Carbonate (2) and ( 4 )
Dichlorovinylene carbonate (2) can be dimerized to form
two stereoisomeric cyclobutane derivatives (550) and
(55h)Ih6' by irradiation in acetone; both isomers yield octahydrocyclobutane (56) which was obtained by West, N i u ,
and Ifdh71on oxidation of squaric acid (57) with nitric acid.
Squaric acid is formed from ( 5 6 ) by the action of SOZ. As
with other hydrated forms of cyclooligomeric carbon monox526
.
..
~
(B!
f 11 )
.
.
I x45
6.13 (s)
~
I09
191
I X40
1x1s
' H - N M R [b].
T [PVI
..
~
~
.
....
I8Y
VC--0
~
(D!
~
M.p. [ C ]
IR [a]:
-
~.
(('1
..
.
I820
I x40
. 6 IO(s)
.-
179-80
I X60
5.9 I
~
~~
(S)
6.09 (s)
.
[a] In K B r .
[b] In [D,]-acetone.
Angew. Chem. internat. Edit.
Vol. 13 ( 1 9 7 4 ) 1 No. 8
ucts at room temperature. Cyclic olefins having r7>3 afford
adducts having typical linkage patterns. For instance, cyclohexene ( 6 5 ) ( n = 4 ) gives a rruns adduct ( 7 1 ) as well as the
miti and syn adducts ( 7 0 ) and (68). Formation of ( 7 1 1 evi-
Hydrolysis of the easily obtainable dimer ( A ) yields the hydroxycyclobutenedione 162)i24.' 17. ''I.
The formation of ( 6 2 ) from dimer ( A ) by hydrolysis allows
conclusions to bc drawn regarding its stereochemistry : The
1,2 arrangement of the CO groups in (62) is obviously due
to the vicinal arrangement of the C1 atoms in ( A ) . and the
ready elimination of water from the intermediate dihydrosquaric acid ( 6 2 a ) suggests a s y n configuration of the carbonate
rings with regard to the four-membered ring.
Recently, Co/e r r t r i . ' l L q l have isolated ( 6 2 ) as baceterial toxin
from F ~ ~ . s u r imoni/iforrnr
m
and Gihhn-r//L/~i~~ikirroi,
and elucidated the structure of its potassium salt by X-ray analysis[' '('I.
The compound, which has been designated "moniliformin",
exhibits biocidal properties.
6.2. Cyclodimerization of Dichlorovinylene Carbonate (2) with
Olefins
Preparation of cyclobutane derivativcs from simplc olefins
and ( 2 ) by sensitized photocycloaddition proceeds readily
Table 5 ('ycloburane deri\%rivt.\ rrorn i2 ) a n d olcfins Scnsitiier: acetophenone o r acctonc: solvent: dioxanc: light
soiirct' H P K 1 3 Philips U V lamp, Pyrcx filter.
_.
..
~
.
...
Olcftn
.
Addiict
~.
Yield
[",<>I
isomeric
['I]
M P
"I
Rcf
comp.
95
49
51
23.2
95
40.5
36 3
41
.
[ a ] The yield
IS
~
~
...
-
.
based on the iirnottnt of ( 2 ) in t h e starting materials (Z.Sniol I scilccnt): olefin concentratton 2.5 mol,i.
and gives good to very good
Experience has
shown acetophenone to be a highly effective sensitizer; diethyl
ether, dioxane, and diethylene glycol diethyl ether have proved
their value as solvents.
As the simplest open-chain olefin, ethylene reacts with (2) to
give the cyclobutane derivative (6.3)["] without side-prod-
dences a multi-step reaction course. The stereochemistry was
established by 'H-NMR
(Table 5 ) .
Proof of a typical reaction sequence with participation of
a diradical intermediate was obtained with (2) and isobutylene
as reactants17'I. At room temperature, only the cyclobutane
derivative(7.3) is obtained. However,at - 70°C compound(75)
also arises. Its formation doubtless involves intramolecular H
abstraction from the diradical (74) which appears to be subject
to hindrance at low temperature.
6.3. The Question of Photosensitization in Cycloadditions of
Dichlorovinvlene Carbonate 12 to Olefins
(68). n
= 4
"syn"
171), n = 4
/ 7 2 ) , n = 10
(6Y), n = 3
(701, n = 4
"anti ' I
Angtw. Chrm. rnrrmat. Edit.
"trans"
1 Yo/. 13
( IY74)
1 No. X
Above 200nm the UV spectrum of pure ( 2 ) exhibits no bands
other than the end absorption. Spurious bands in the 300-360nm[201rangeareduetooxalylchloridepresentasimpurity[701.
If the excellent sensitizing effect of acetophenone (ET= 74 kcal/
m 0 1 ) [ ~or
~ ] acetone (ET= 79.5-82 kcaI/m01)['~~.
in cycloadditions of ( 2 ) with olefins is interpreted as being due to triplet
energy transfer, then the energy ET of the lowest triplet level
of ( 2 ) would have to lie <74kcal/mol above the ground
state.
PPP calculations[741as well as quantum yield measurements
on sensitized cycloaddition reactions with application of sensitizers of decreasing triplet energy[751reveals that the lowest
triplet term of ( 2 ) is 68-70 kcal/mol above the ground state.
527
Moreover, the quenching constant for the Norrish Type I1
cleavage of butyrophenone by (2) is found to be
k , = 5.6 x 10’ 1 m- I s- 17‘]. These results suggest that a tripletenergy transfer from the above sensitizers to (2) is very likely.
The photoreaction of (2) with furan to give ( 9 0 ) , ( 9 2 ) , and
( 9 4 ) (see Section 6.5) again belongs to the class of sensitized
photocycloadditions, i. e. in the absence of sensitizer, e. 9. acetophenone, no reaction occurs.
The photopinacolization of acetophenone on irradiation of
its ethereal solution, which was observed by Ciamicia and
Silber17’l, is suppressed only slightly by furan, but strongly
in the presence of furan and ( 2 ) , in favor of photoadduct
formation [ ( 9 0 ) , ( 9 2 ) , (94)][”l.
Although the intermediate existence of a 1,4-biradical such
as (78) cannot be completely ruled out on the basis of these
results, we again favor triplet-energy transfer from ’Sens* to
(2).
The same applies to the photosensitized dimerization of (2)
to ( 5 5 a ) and ( 5 5 h ) and of ( 4 ) to ( 6 0 ) and (61).
butane series or their hydrate forms on hydrolysis. It frequently
proves possible to briefly observe the typical UV s p e ~ t r a [ ~ ” ~ ~ l
of 1,2-~yclobutadiones[~~”l which have meanwhile become
accessible by another route. They can also be trapped by
phenyl hydrazine, but resist isolation[86! Instead, they rearrange to sc-hydroxycyclopropanecarboxylic acids, e. g. ( 6 3 )
affords ( 7 9 ) , in protic solvents[’7. 8 7 1 .
This reaction, which renders the u-hydroxycyclopropanecarboxylic acids readily accessible (Table 6), displays an interesting stereoselection. The stereoisomeric cycloadducts ( 6 7 ) and
( 6 9 ) should afford the two likewise stereoisomeric 1-hydroxybicyclo[3.l.0]hexanecarboxylic acids ( 8 2 ) , m = 1, and (83),
m = 1, respectively, since the carbeniurn ion resulting on opening of the cyclic cation (80) can escape both “upwards” and
“downwards”. The sarne‘applies to ( 6 8 ) and (70). However,
isomers of type (83) are formed exclusively without any detectable trace of the isomeric compounds (82).
Table 6. 3-Hydroxycyclopropane derivatives.
- .-
CPd
-.
~
-
(79)
( 8 3 ) . m= I
(831, m = 2
(84 i
.-
M.P. [ C l
-
~-
Yield [ % I
~~
I 08
I06
129 -130
161
95
85
81
73
~
-
Ref
__
~
[17, 85, 891
P61
[861
1691
6.4. Synthesis of cc-HydroxycyclopropanecarboxylicAcids
Compounds (63) and (67)-(72) possessing potential cc-diketo functions should transform into cc-diketones of the cyclo-
(671, m
(68), m
=
1
=
2
Since similar results are obtained on protonation of bicyclo[m.2.0]alkane-(m 3), ( i4)-diones, which have meanwhile
become availableLE7.
‘I,
formulation via the intermediates of
type (80) and (81) is justified. The reason behind this stereoselectivity has not yet been elucidated.
+
\
I
r
(86 hi. frans
l Y 6 a i . cis
Solvolysis of the tosylates of (83), m = 1 and m=2, and of
( 8 4 ) proceeds via a disrotatory opening of the cyclopropane
ring with ring expansion to give P-hydroxycycloalkenecarboxylic acids. Thus equimolar amounts of the P-hydroxycyclotridecenecarboxylic acids ( 8 6 a ) and ( 8 6 b ) are obtained from
( 8 4 ) or (85)[691.
528
Angew.
Chrm. internat. Edit. 1 Vol. 13 ( 1 9 7 4 ) 1 No. 8
6.5. Dienes as Cycloaddition Components
The photochemical cycloaddition of ( 2 ) to I ,3-dienes proceeds
with a widely varying degree of success. 2,5-Dimethyl-2,4-hexadiene affords two stereoisomeric adducts ( 8 7 ) in only moderate yield‘”’. The reason most probably lies in the excellent
quenching properties of the dienes towards photoexcited
ketones, which strongly reduce the sensitizing action.
0 0
K
(87)
2 isomers
tane derivatives ( 9 1 ) and ( 9 3 ) . A photochemical e.uo-[4+ 21cycloadduct analogous to the furan derivative ( 9 4 ) is not
observed in the case of thiophenel”’!
Methanolysis of ( 9 0 ) and ( 9 2 ) in the presence of sodium
carbonate proceeds ria a series of consecutive reactions to
form the sodium salt of the dienologous carboxylic acid
(96)[261,
a derivative of glutaconic dialdehyde. The sodium salt
( 9 5 ) is deep red in aqueous solution, whereas the dienologous
acid ( 9 6 ) is yellow. They co-exist in a pH-dependent reversible
equilibrium : the system can therefore be employed as an indicator.
The substance reduces Fehling’s solution and gives violet
colorations typical for p- and 6-dicarbonyl compounds with
Fe3+.
6.6. Alkynes as Cycloaddition Components
H3C\
(UO),
(Ul),
x
= 0
x=s
(92), x = 0
(93), x = s
( 94)
Acetylene[”’] and 2 - b ~ t y n e ~are
~ ~ suitable
I
for sensitized
[2+ 21-cycloaddition to (2). In solution at room temperature,
( 9 7 ) is formed in only poor yield from acetylene and (2).
The cyclobutenedione ( 9 8 ) has nevertheless been prepared
in this way by subsequent hydrolysis of ( 9 7 ) .
The photoreaction of (2) with 2-butyne proceeds less clearly.
The product ( 9 9 ) is accompanied by (101) and ( 102). However, product analysis and the temperature and solvent dependence of the reaction d o provide an insight into the pertinent
cycloaddition mechanism. Both ( 9 9 ) and ( 1 0 1 ) arise from
a common photochemically generated intermediate ( 103)
which must possess a strongly polar structure since it is stabilized only in polar solvents such as acetone or acetonitrile.
It eliminates CO2 to form the cyclopropene derivative ( 1 0 1 ) .
Intermediate (103) is essentially a 1,4-diradical ( 1 0 3 ~ which
)
collapses to a 1,4-dipole (103b) in an intramolecular redox
<reaction;ring closure to the cyclopropene system occurs with
loss of c02.
However, 3-hydroxychrysanthemumic acid ( 8 8 ) cannot be
isolated on hydrolysis: the tautomeric keto form ( 8 9 ) appears
very readily. Experience shows that thea-hydroxycyclopropanecarboxylic acids having a double bond conjugated with the
three-membered ring yield the tautomeric keto forms very
rapidly.
(971, K
199), R
The yields obtainable from heterocyclic dienes such as furan[’61
and thiophene[’6, 1‘’ again vary widely. While furan affords
the isomers ( 9 0 1 , ( 9 2 ) , and ( 9 4 ) in the ratio 16:25:9 (60%
overall yield), thiophene furnishes only 9.5% of the cyclobuAngew. Chem. inturnat. Edit.
Val. 13 ( 1 9 7 4 ) I N o . 8
=
H
=
CH3
(98), K = H
(100) , K = C H3
An activation barrier must exist between ( 1 0 3 ~ and
)
(103h)
since only ( 9 9 ) is formed at low temperatures. trans-2.3-Dichloro-2,3-dimethylcyclopropanecarbonylchloride (102) arises from (101) in a dark reaction by the action of hydrogen
chloride formed as side-product in the photoreaction. Formation of ( 1 0 2 ) can be rationalized as involving an intermediate
529
cyclopropenylium ion, and can be accomplished with pure
( I O J ) and HCI. Hydrolysis of ( Y Y ) yields dimethylcyclobutenedione (100) which is identical with the product obtained
by Bloriiqirist and Vierling viu an alternative route'"'].
subject to nucleophilic attack by a further molecule of maleic
anhydride in the course of the reaction, leading to stereospecific
formation of the known 2: 1 addu~t["~.
Meanwhile, further experimental results have shown how olefins and dienes undergo photochemical cycloaddition to benzene["' - Io3'and naphthalene, and Bryce-Stnifh has collected
a number of fundamental cases of symmetry-controlled cycloadditions to benzene under photochemical condi-
ti on silo^. 1091
I
Accepting this concept, then a concerted 1,2- or 1,4-cycloaddition with retention of configuration at the linkage sites is
"allowed" only if the added molecule reacts from the S , state
with So benzene or if benzene reacts from the S2('BI,) state
with the SOolefin. In contrast, reaction of Sl('B2.) benzene
with the SOolefin is symmetry-forbidden so long as no charge
transfer complexes or exiplexes of the reactants are
involved~10I.Io31
intersystem
crossing
The study of the photochemical addition of (2) to benzene
and naphthalene commanded not only preparative interest,
as repeatedly mentioned, but mechanistic interest too, because,
in spite of claims to the contrary"". I l o ] , no charge transfer
complex between the reactants could be dete~ted'~"].
In general it may be said that the photocycloadditions of
(22) to alkynes at room temperature give much lower yields
and are usually less selctive than to alkenes. At low temperatures (-30 to -4O'C), however, the adducts ( 9 7 ) and (YY)
are obtained exclusively as homogeneous products. Hence
the reaction can compete effectively with other more complicated procedures[9S1.
7. PhotochemicalAdditions to Benzene and Naphthalene
The classical photochemical cycloaddition of maleic anhydride
to benzene provided the impetus for an understanding of
the use of simple aromatic compounds as cycloaddition
partnersIY6-' " 1 .
It was deduced from a large number of studies that the actual
reactive species in the case of maleic anhydride and benzene
is a charge transfer complex of the
which is
Onphotoadditionof(2) to b e n ~ e n e [ i'o-'1.31with
~ ~ . ~ ~ . acetophenone or 2-butanone as sensitizer, only the 1,2-cycloadduct
(104 b ) can initially be isolated from the mixture after brief
irradiation since it crystallizes from the reaction mixtUre1111.112.701
On further irradiation the concentration of (104 h ) steadily
decreases in favor of the 1,CcycIoadduct ( 1 0 5 ) and the two
stereoisomeric 2 : 1 adducts (106b) and ( 1 0 6 ~ ) Since
.
the
2 : 1 adduct ( 1 0 6 u ) can also be isolated, it has to be assumed
that the endo-isomeric 1,2-cycloadduct ( 104a) is formed but
presumably undergoes very fast reaction and thus escapes
detection owing to an insufficient steady-state concentration.
In the presence of the sensitizers employed, the isolated exo
1,2-adduct is partly cleaved to the starting compounds and
partly rearranges to the 1,4-adduct ( 1 0 5 ) . The above time
dependence of the concentration of ( 104 h j becomes understandable in the light of these observations.
(104a), endo
(104b),
ex0
I
hydro1
(106a). endo - endo
530
(1066), endo-exo
( I ' Q ~ C ) , exo-exo
Angew. Chem. intrmat. Edit.
1 Val. 13
(1974)
No. 8
Howcver, the structure and stereochemistry of the products
have been established. The I ,4-adduct ( 1 0 5 ) I S formally the
Dieis.-Alder adduct of ( 2 ) to benzene; the adduct cannot
be obtained by a thermal route. This compound proved to
be a suitable starting material for the preparation of the
bicyclo[2.2.2]octa-5,7-dien-2,3-dione
hitherto
unknown
( 1 0 7 ) l ’ I which, unlike the non-isolable homologous norbornadien-7-one’” ‘), is fairly stable thermally. However,
( 107) undergoes very ready photochemical decomposition
to benzene and carbon monoxide.
h”
1
.1
Unlike benzene, naphthalene possesses no degenerate energy
levels owing to its lower symmetry. Thus the symmetry disqualification postulated by Bryce-Smith for the S , state of benzene[”” does not apply to a concerted process from the
S 1 state of naphthalene.
Reaction to give the 1.4-cycloadducts (IOY) then takes place
from a triplet state of (IO8) which can be occupied either
by addition of a sensitizing agent, r.y. acetophenone, or by
triplet-excited naphthalene itself. (Excited naphthalene has
a significant intersystem crossing rate“ ‘‘I so that IP-adducts
can also arise in the absence of a sensitizer.) The reason
for 1.2-adducts ( I O N ) not undergoing immediate reversion to
naphthalene and (2) on direct irradiation is that they absorb
at shorter wavelengths than naphthalene and can therefore
be largely protected by use of suitable filters.
Hydrolysis of the 1,4-isomer ( I O Y j affords the diketone ( 1 1 0 ) .
which is likewise very stable thermally but is subject to extremely ready photochemical decomposition to naphthalene
and carbon monoxide.
( 1 0 8 ~ ) .ex0
hvlsens
The 1,2-adducts (108) are formed from the Sl cxcited state
of naphthalene which is trapped by (2). We are therefore
dealing with a singlet reaction of naphthalene.
h”/sens
8. Conclusion
Observations performed to date on the chemistry of halovinylene carbonates show that this relatively young class of compounds will assume a place among the synthetic reagents
of organic chemistry owing to the variety of their possible
applications. In spite of the tentative nature of some of the
results and a number of unsettled optimization questions,
these derivatives have opened the way to molecules whose
formation reaction will stimulate further preparative and
mechanistic studies.
(1090), ex0
hydro[.
(110)
’’
On irradiation of naphthalene/(2) solutionsl 5 1 under conditions ensuring that only naphthalene can absorb light, the
primary products, as in the case of benzene, are the isomeric
1,2-adducts ( 1 0 8 ~ and
)
(108b), and after prolonged irradiation the 1,Cadducts (10Ya) and ( l o b ) . All compounds have
been isolated and their stereochemistry established by HN M R spectroscopy with the aid of lanthanoid shift reagents“ 1.
’
‘
O n selective irradiation in the longest wavelength absorption
band of naphthalene the same reaction course is operative
as is observed on irradiation with the unfiltered light of a
high pressure mercury lamp. The initial products are the
1,2-cycloadducts ( 1 0 8 ) which then disappear in favor of the
1,4-cycloadducts (109). Preparative isolation of the 1,2adducts (ZOH) from the reaction mixture therefore proved to be
more problematical than that of the 1,4-cycloadducts.
The 1,4-adducts ( I O Y ) , which may also be regarded as the
thermally inaccessible “Diels-Alder adducts” of naphthalene
to (2). can be isolated in good yields by exhaustive irradiation
or by use of acetophenone as sensitizer.
Sterically pure ex0 and endo 1,2-adducts ( 1 0 8 a ) and ( 1 0 8 b )
regenerate (2) and naphthalene quantitatively on direct irradiation. In the presence of sensitizer, however, they undergo
> 80 ‘/o stereoselective conversion into the corresponding 1,4cycloadducts ( I O U ) . Mechanistic studies reveal the following
picture of the naphthalene/(2) system:
Angew. Chrm. internat. Edit.
Vol. 13 ( 1 9 7 4 ) 1 N o 8
Work,fron~
our laboratory reported in this strrryr was goirrou.slj~
supported by the Deutsche Forsc~hitngsgeniein.sc/iqft.the Aint
, f i r Forsc~hirngties Larides Nortlrhein- Westfiifon,utul tho Fonrls
rler Chmiischen inrlusrrir. 1 worrlrl liko t o link nij9 t h a n k s t o
these institutions with an expression of gratitude to m y coworkers for their skill and engugement which made these r~.sults
possible.
Received: September 10. 1973 [ A I I If:]
G e r m a n versioii. Angew. Chem. X6. 567 (1974)
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W Erb, Dissertation, Technische Hochschule Aachen 1974. T h e cycloadduct of f 2 ) a n d 1.2-dimethyl-I-cyclohexenehas meanwhile been hydrolyzed
t o I,6-dimethylbicyclo[4.2.0]octane-7.8-dione
[87] See also refs [84], [X2], a n d [88].
[XX]
H . G Heinc. Bayer AG, Cerdingen-Krefeld, personal communication
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[46] M p. 200 C: J . Stroriny, B. Zwunrnhnrg. A Wuymorir, a n d A . C. Udding,
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[47] M . p 199-201.5"C:
22, 52X (1957).
[SS]
[X6]
[92] J . C . H i n d m y , Chem. Commun. 1Y71. 630.
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W R. I'unyhan a n d M. Yr,shimine, J. Org. Chem.
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I.
[IOO]
(I967).
[52] A mass peak of nilr 56 is given in ref. [46] a s occurring in the MS
spectrum of ( 4 5 ) . It is assigned to C202.
[loll
[83] J . F/c~i.schhuurr,M . B i d e r s , a n d H . D. S h i v / , Tetrahedron L e t t , in
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[54] f f . D. B r r w v , H . Moesru, a n d N. Truppm, Chem.-Ztg. Y4, 129 (1970).
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Kiisters.
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S. Irdun, a n d A. P. Murr,bunr/. Tetrahedron
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91x.
[I091 D Bry<,c~-Sniirh,
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532
[Ill]
Angew. Chem. internat. Edit.
1 Vol. 1 3 ( 1 9 7 4 ) 1 No. 8
[ I 151 ./. 4r-t.r: Dissertation. Tcchnische Hochxliulc Anchcn 1973: C'hcm.
Hcr . in p r c s
[ I 161 I'opulation of thc naphthalene triplcr
G ('(iiicrr ,ind .I
York 1966. p. 309.
8
io Intcrsyctcm crossing amounts
Photochcmistry Wiley. New
,V. Plrr.5
t o Q>,,,=O.39 J
[I171 M.p 163.C (dec.) IR ( K B r ) . v c o . 1890. 1800. 1740cni-'. vOH.2800
22OOcm- ' : v = <
3lSOcm- I . ' H - N M R (15mg / 6 2 ) 0 5 m l [D,]-acetone):
T = 1.19 l l H . 51. 2.53 I l H . s). M W IMS): 9X. L V [ether. nrn ( E ) ] . 213 116404).
~
731 lXii4). 308.5(23.7). 371 (14.5):C V [ H 2 0 , 1.9Xx 10 ' v : nm I t : ) ] : 2575
(8283). 227 (2x636): [HrO, 9.9 x I O - ' M : nm C&)]382 (9.4)
[ I i X ] Scmisquaric acid 1 6 2 ) has hecn prcpared by R W f / o / ~ ~ m m i Ci .' .
Bi-cssd, I . G~41ll1~iiis.
and f l H u i i w r . Chcm. Ber. 104, X73 (1971). by an
alternative route
[ I 191 R. 1. ('olr. 1. W Kiri,x,j. H. C . c'urkv. B. L. DoiipiiiL. and 1. c'
i'(v Cham. Science 179. 1324 (1973).
[ I201 I . P. Springer. 1. (./urd)., R. 1. c ' o / ~ I. W Kirk.wr, R. K .
f/i//.
R
.M. Cur-hoii, and I . L Isidor. J. Amcr. Chcm. SOC. 96, 2267 (1974).
C 0 M M U N I CATION S
Reaction of 1,3-Oxazin-6-ones with Ynamines and
Ketene N,O-Acetals
By Wolfgang Steglich, Ernst Buschmann, and Oswald Hol[irzrr"'
I ,3-Oxazin-6-ones (3)[11 open up interesting preparative prospects that have hitherto been little explored. We have found
that 4-niethyl-1,3-oxazin-6-pnes(3a)-(3c) (Table 1) can be
prepared from 2-(acylamino)crotonic esters (/) by heating
them in a metal-bath at 270°C and distilling off the alcohol
that is formed[2];the reaction may occur by way of ketene
intermediates (2)[31.
formed on reaction with 1-ethoxy-N,N-dimethylvinylamine14'
(Table 2). The reactions of (3a)-(3c)
in ether are complete
within a few hours, but cooling is necessary with (3d) because
of the strong evolution of heat.
/
(3)
r
H
H
I
- COI, -CzHrOH
R
H3C ANA
(5)
Table 2 4-(Dtalkylamino)pyridines ( 4 ) and 1 5 ) prepared [a]
Yield
[% 1
- - ---
Table I. 4-Methyl-l.3-oxazin-6-ones ( 3 ) prepared [a].
.
..
-.
- - .. -. -. Cpd.
R
Yield
~
~
~
~
~
~
~~
~
~
- -
~
B. p.
[ C/torr]
["A)]
.
.
-
(,hi
(CH.3j2CH
(CHJ)?C'HCHz
(31.)
(CH3)3C
l3Ui
...
-
40
60
52
--
--_
40 -4210.1
41-49/0.15
39 -41103
66--69112
- - - ._
[a] All the compounds gave correct elemental analyses.
[h] From iert-hulyl 3-aminocrotonate and trifluoroacetic anhydride.
The 2-trifluoromethyl derivative (3d) was obtained from (errbutyl 3-aminocrotonate by the action of trifluoroacetic anhydride at room temperature. The 1,3-oxazinones (3a)-(3c)
show characteristic bands in the IR spectrum (CCI,) at 1770,
1632 and 1580 cm-' [ ( 3 d ) : 1795,1655 and 1595 em-'] and
NMR signals for the methyl group and the vinyl protons at
6 = 2.18 (d, J = 1 Hz) and 5.9 (q, J = 1 Hz), respectively [( 3 d ) :
6 = 2.38 and 6.251.
Reaction of the 1.3-oxazinones with N,N-diethyl-I-propynamine affords 2,3,6-trisubstituted 4-(diethylamino)pyridines
( 4 ) ; and 2,6-disubstituted 4-(dimethy1amino)pyridines ( 5 ) are
[*] Prof. Dr. W. Steglich, Dip1 -Chem. E. Buschmann, and DiplLChem. 0.
Hollitzer
Organisch-Chemisches lnsiitut der Technischen Universitdt
I Berlin 12, Strasse des 17. Juni Nr. 135 (Germany)
Angrw. Chrm. intrrnat. Edir.
M. p.
B. p.
[ C/torr]
.--
~.
- .
-
r CI
64-6610 2
77--7n10.2
7810.1
66--68 10.2
63-64/0.2
7n--7910.1
73
75.5
[a] All the compounds gave correct elemental analyses
65
CF,
( 3 d i [h]
19
89
65
61
XO
90
94
80
_
/ Vol. 13 (1974) / No. H
The orientation of the substituents follows from the NMR
spectra. Thus ( 4 d ) shows an H,F coupling of 2.3 Hz between
the trifluoromethyl group and the methyl group in position
3. For the terf-butyl derivative (5c) the aromatic protons
appear as an AB quartet at 6=6.20 and 6.37 (5=2.5 Hz)
but for (5a) and ( 5 h ) as a single signal. The 2-trifluoromethyl
group in ( 5 d ) causes a shift of the AB quartet to 6=6.52
and 6.79.
Their diene character determines the course of reaction of
1,3-oxazinones with electron-rich multiple bonds, whereas with
3,l -benzoxazinones the anhydride system from carboxylic and
imidic acids also plays an important part[']. The regiospecificity observed corresponds to attack by the nucleophile on
the C=N group of this system.
2-tert-Butyl-4-methy/-I,3-oxazin-li-one
(3c)
Ethyl 3-(pivaloylamino)crotonate (105 g) ( I c) was heated for
3 h in a metal bath at 270 C, the ethanol formed distilling
off through an air-condenser. Distillation in a high vacuum
afforded a colorless oil (49 g, 60 %).
533
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