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Dynamic Stereochemistry of the Degenerate DiazaCope Rearrangement.

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Yield. reaction conditions. iind -/ Y ratios in the reactions of ( I ) with electrophiles to give ( 2 ) + ( 3 ) .
Table I
__
.
~
I:'
.~
... ..
.. -. .
~
~
EL
. _. .
.~
C ' l i Br
~-
~ .
C~HIBI
Ii-CioH 2 1 Br
C,)HiCH2Br
i i - C I , I H 2Br
1
C,,H ,CH?Br
ll-C7H,,('1
ii-C<,Ht.I Br
ii-CKHl-Cl
i-CrH-CI
(CH > \ 6 i C \
2,Z-Dimethyloxirane
<''Hic'HO
(iI1.C.f 1 0
Cyclopentanone
(.c,H <COCHI
(CoH<)'CO
CH ISSCH j
~~
. ~ .
Yields
[ '7.3
Ial
of(zi+(3J[b]
A
A
A
65
90
67
75
90
87
80
76
86
69
89
70
95
88
70
-!1
Ratio
..
(')I ? I
c
CH $ 1
CI1,I
CI,HICH'Br
C,,H ;CH ZBr
2,2-Dimethyloxirane
CH.tI
CHII
CHAI
CHzl
CHJI
CHII
C
c'
I= f
3 i]
~
c
B
A
B
C
C
c
c
B
..-~
_
77 23
77.23
73/17
76 24
78,'22 [c]
74 26
6X. 32
76/24
78/22
74.26
80,120
__..
~- .[a] A : 2.1 equivalents of E ' are added at - X O C by syringe. then the mixture is allowed to warm to 20 C overnight.
B: ( 1 ) 1s reacted uith 1.03 I I equivalents of t' for I 11 at -80 C. 1.1 equivalent of E' is added. and the mixture
jbarmed to rooin temperature.C: as B. but E' is added u / ! w slowly warming to room temperature. Workup see
ref [4].
[h] The yields (not optimized) were determined by NMR spectroscopy of the crude products of 2.- IOmrnol runs
[c] See Scheme I , compound ( 4 ) .
.
. .
~ . . -~
~-
-~
.
Reaction
conditions
~
.
~
.
~
.
~
.
~
-
~
.....
-1
(u). X = 0; ( b ) , X = (OCH,),
[3] E . J. C m q and B. W E t . i i . k . ~ ~unpiibiished
i.
results 1966.!67; B. W
Ericisoii, PltD thesis, Harvard University 1970: J . F . Bic//nicrnn and J . B.
Duceh, Tetrahedron Letters IY6K, 5629: IY6Y. 3707: K . Kolido rr ul.. Chem.
Commun. 1972. 131 I : D. Srrbodi. M. Koib. and B.-Th. G r i h i . Angew.
Chem. 8s. 42 (1973): Angew. Chem. internat. Edit. I?. 69 (1973). P L,.
Srotiri. and R. E Hortiish, J. Amer. Chem Soc. Y.5. 4444 (1973): K . Oshiniu
cr u . . ihid. 95. 2693. 4446. 5803. 7926 (1973): D. 4. Errins and G . C. Aiiclrrn.s,
Accounts C h e m Res 7. 1974. i n press. and literature cited therein.
[4] Doubly metalated thiohenzyl alcohol: D.Seebach and K.-H. Geiss. Angew.
Chem 86, 202 (1974): Angew. Chem. internat. Edit. 13, 202 (1974).
[5] Prof. M. Sr/ifo.ssrr.Lausanne. kindly informed us that 2-propcne-1-thiol
and 3-methyl-2-butene-I-thiol have been doubly metalated independently
in his laboratories
161 Determined from the NMR integration ratios of the following signals:
?-sulfur hydrogens of the group E'. the vinylic I"wits all other hydrogens.
and the terminal vinylic hydrogens I crsiis all vinylic hydrogens. The NMR
spectra of some of our products aie identical with those described by B.
W. Eiicirron (Thesis, H a n a r d University 1970) who obtained compounds
( 2 ) and (3) from metalated thioallyl ethers. All new products show spectra
in accordance with the structures given here.
[7] E . J . Corer. and B. W
Scheme I . Sulfur-free products from adducts ( 4 ) and (8) of the dianion
(;ill reactions Mere carried out at 20 C). 141-+151: CH.$SH!HCI &%is
in benzene, 3min, 1007;;
/ 4 ) - ( 6 a j : 4,5 equiv. NBS in acetonitrile/H,O.
2min. 73%; (41-(6b):
as above but in anhydrous CH,OH, 85",,:
( 5 ) - ( 7 u ) : 4.5 equiv. NBS, 5 equiv AgNO, in acetonitrile/H,O. 3min.
6 0 % : ( 5 ) - ( 7 h ) : as above but i n anhydrous C H 3 0 H . 7 0 % : / 8 ) + ( 9 ) :
4.3 equiv. NBS in CH,OH. 2min. 7 4 %
(1)
conversion of methyl vinyl thioethers such as (4) into aldehydes ( 7 u ) which involvesaddition ofthiol to forma thioacetal
( 5 ) that is subsequently hydrolyzed by known methodsE2'.
N-Bromo~uccinimide~~'
converts ( 4 ) into the rx-bromo aldehyde ( 6 u ) in aqueous acetonitrile, while the bromo acetal
( 6 h ) is produced in methanol; similarly, the cyclic brorno
acetal ( 9 ) is formed from the benzaldehyde adduct (8).
Received: May 15. 1974 [ Z 30 IE]
German version. Angew Chem. K6. 484(1974)
[ I ] From the PhD thesis of K.-H. Griss and the Diplomarbeit of B. Swi'iny,
Universitiit Giessen 1974.
[2] Reviews on Umpolung of carbonyl reactivity: D. Seebach and M . K o f h ,
Chem. Ind. (London), IY74, in press; D. Seebach,Angew. Chem. 81,690(1969);
Angew. Chem. internat. Edit. 8, 639 (1969); D. Seebach, Synthesis 1969. 17.
and literature cited therein.
480
Ei.ic/,.\oii,
J. Org. Chem. 36. 3553 (1971).
Dynamic Stereochemistry of the Degenerate DiazaCope Rearrangement[**]
By Fritz Viiqtle and Ernst Goldschmitt[*]
A further milestone was passed in the theory ofvalence isomeri-
zation when, in 1971, Dewar"] postulated that 3,7-diazasemibullvalene has to be formulated as a nonclassical molecule
[bishornopyrazine (1 )] in the ground state.
While experimental proof of this prediction is still forthcoming,
the recently described thermal valence isomerization of 1,3,4,6[*] Prof Dr. F. Vogtle and Dlpl.-Chem. E. Goldschmitt
lnstitut fur Organische Chemie der UniversitPt
87 Wurzburg, Am Hubland (Germany)
[**I
This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
A n g m . Chrm. internat. Edit. Vol. 13 ( 1 9 7 4 ) 1 No. 7
d ) 208OC
(2)
i n ) , A r = phenyi
ih). A r =4-methylphenyl
( c ) . Ar = 4-merhoxyphenyl
(2'1
I d ) , Ar =4-cyanophenyl
( e l , Ar=4-pyridyl
if), Ar=Z-pyridyl
H
..C//N
J
H
44.
m
m
tetraaryl-2,S-diazahe~adienes~~~,
whose tleyenerute variant
( 2 ) ~ ( 2 'is) reported in the present communication, permits
analogous studies of heteroatom and substituent effects in
a nonbridged model system.
At elevated temperatures (above 120-C in D6-DMSO) the
diaza-Cope rearrangement ( 2 a ) g ( 2 a ' ) of N,N'-dibenzylidene-l,2-diphenylethylenediamine leads to an equilibrium
between meso- and d,l-valence isomers in the ratio I : I , irrespective of whether the reaction starts from meso-(Za) (m. p.
171-173 C ; 164-165 C'") or d,l - ( 2a) (m.p. 159-160 C).
This was established by proton magnetic resonance comparisons with authentic mrso- and d,l compounds (Fig. 1).
Thus the deuterium-labeled azomethine meso-(3) obtained
on reaction of nzeso-1,2-diphenylethylenediaminewith [formyl-D]-benzaldehyde affords a completely equilibrated 1 :I:I:I
valence isomer mixture of meso- and d,l-(3) and -(3') whose
components can be distinguished by their proton resonance.
An analogous equilibration is observed starting from tneso-i4/.
m
c ) 187OC
I
d. I
Comparison of the 'H-NMR signal intensities at 139, 146,
and IS2 C as functions of time affords an approximate value
of 31 kcal/mol for the free enthalpy of activation AG * of the
d,l+tneso transition of ( 2 a ) which is to be regarded as constitutionally but not configuratively degenerate.
It is particularly appealing that the degenerate diaza-Cope
rearrangements can be observed directly by dynamic 'H-NMR
spectroscopy (Fig. 1): on heating of a sample of d , l - ( Z u j
dissolved in D,-DMSO the initial reaction is the above
rl,l~mnrsoisomerization, which is readily recognized by appearproton resonances of the meso comance of CH=N-CH
pound. A further increase in temperature leads to increasing
broadening of the H',H3- and HS,Hh signals of the r/,/ form;
they again appear as sharp singlets on cooling of the sample
haciriy ci,flirctionuf
solution. Accordingly, d,I-(Za) is a niolec~rli~
sfrucfure at elevated temperatures.
The free energy of activation at the extrapolated coalescence
temperature (T,.=22&230°C; Av=209Hz) has a value of
23-24kcal/mol and is thus lower than in open-chain Cope
systems (1,5-he~adienes)~'!Remarkably, the signals of meso( 2 0 ) remain as sharp singlets in this temperature range (Fig.
1). This finding is in accord with calculation^['^^^ and experimental
which indicate that the boat-like six-center
transition state-which would have to be traversed in the
case of a valence isomerization m r s o - ( 2 a ) ~ m e s 0 - ( 2 u ' ) [ ~ l requires a higher activation energy than the chair-like fourcenter transition state which is to be assumed for the d,l$d,l
conversion[61.A further argument for the greater tendency of
the d,l form to rearrange compared to the meso form could lie
Angrn-. Chem. internaf. Edit. J Vol. 13 ( 1 9 7 4 ) 1 No. 7
I
in the d,l compound being conformationally more favorable
for the chair transition state whereas the conformation of the
meso compound is unfavorable for the boat transition state.
This becomes clear on consideration of molecular models.
For kinetic determination of the activation parameters of
the d,l$d.l valence isomerization, we resolved racemic 1,2diphenylethylenediamine into the antipodes with the aid of
optically active tartaric acid"]. ( + ) - ( 2 u ) and (-)-(Zu) were
obtained in crystalline form. Their racemization, which is
due to a [3.3]-sigmatropic shift, was pursued by polarimetry
a t several different temperatures. The rate of valence isomerization is already too high for polarimetric measurements at
70 C. Racemization of the optical antipodes in the course
of the diaza-Cope rearrangement is readily understood in
48 1
vie\\ of the mirror image geometry of the substituents in
the transition state (Fig. 7). The rearrangement obcys first
order kinetics at all temperatures (k31,8 c=5.23 x lo-'?
k,,
,.=ISOX
k,j,O .=2.39x lo-", k 4 8 , h .=3.53x
lo-'). The activation energy E , for the degenerate diaza-Cope
rearrangement is found to be 21.8 kcaljmol. Interestingly, a
value of 23.9kcal/mol is obtained for A G * . which agrees with
that determined by the coalescence method. As expected, the
entropy of activation is strongly negative: AS* = -7.5cal
deg- mol- '
R+NTHR
H
:Z3LZ7
I-is 2. R x c n i i / a t t o t i ( S . S ) - ( 2 ) - ( R , R ) - ( ? ' ) o r ( R . R ) - ~ ~ j ~ ( S . S T) -h(e ~inir
'~.
r o r image in thc triinsition state is s h o w n gray.
The degenerate diaza-Cope rearrangement even appears to
take place in the solid state: crystals of ( - ) - ( 2 n ) lose their
optical rotatory power within 24 h.
Introduction of o, n 7 , or p substituents into the four aromatic
nuclei of ( 2 ) leads to further degenerate diaza-Cope systems.
The compounds studied hitherto confirm the results obtained
with the unsubstituted system ( 2 a ) : only minimal changes
arc found in the activation parameters of ( 2 h ) and ( 2 ~ ) .
In the presence of electron-attracting substituents as in (2ci)( 2 f J avoidance reactions occur which are possibly attributable
to an irreversible cleavage of the weakened ally1 o bond.
The considerable influence of the 3,4 phenyl substituents of
( 2 a ) is underlined by the lack of any tendency of N,N'-dibenzylideneethylenediamine to undergo rearrangement at 210°C.
Recetccd. April 30. 1974 [7 34 I E ]
G e r m a n \erston: Angcw. Cheni. 86.520 11974)
[ I ] M . J . S. Drwar a n d D. H . Lo, J Amer. Chem. Soc 93. 7201 (1971).
\I J . S Lkn~ii.. L. . V d i / o t h i . and U. : X d t l ~ i i \ A ~ i C'liem.
.
Commun. ! 9 ? / .
1373: cf. also R. Ho//nior7t7 and U! D. S i o h r i ~ .1. Amer Chem. Soc. YZ.
esis that the multiply annelated four-membered ring is responsible for this behavior was to be tested on a model of cis-tris-ohomobenzene systems having a longer bridge, e.6~.( 8 ) or
( 9 I . [271+ 201-photocyclization of the bishomobarrelenes (5)
or ( 6 ) appeared a likely method for their preparation.
These expectations were not fulfilled however; photoreactions
with various mlo,exo-bishomobarrelenes ( 5 ) (X,X'=CH2,
CHCOZCH3,0, NR'; R=C02CH3, CF3, CH3) afford almost
exclusively the trans-tris-o-homobenzeneproducts (7), which
are incapable of 3 ~ + 3 7 topening, with participation of the
three-membered ring anti to the excited chromophore. The
c.ndo,endo-bishomobarreIenes (6)-both
possibilities of
[2n + 201-addition lead to cis products [ ( 8 ) ,(Y)]-are, however, inaccessible. Regardless of the nature of the three-membered ring in (4)(X'=CH2,CHCN, 0),the second three-membered ring is only formed from the e.w side (X=CH2,
CHCO,CH,, 0, NJX') to give ( 5 ) under a wide variety of
conditions'', 31. The steric conditions and the proclivity to
rearrangement of the tricyclo[3.2.2]nonane skeleton also
thwarted attempts to bring about a transition ( 5 ) --t (6) by
way of known substitution and cyclization steps131.
This uxo-endo isomerization is however possible at the stage
of (7). The "trans-oxide" (7) (X=O, X'=CH2, R=CF3)13],
which is accessible from ( 5 ) ( X = O , X'=CH2, R = C F 3 ) on
a preparative scale by direct photoexcitation and is highly
resistant to attack by nucleophiles, undergoes smooth reaction
in a 2 N sulfuric acid solution in DMSO to give the crystalline
trans-diol ( I O U ) (72%: m.p. 112.C: r=5.87 (Hb),6.26 (H');
Jb.a=4.2,Jb.==6,Jc.d=OHz; CD3COCD3, 270MHz). The
action of c u . 1 equiv. of tosyl chloride (pyridine, 20"C, 3d)
results in 60% conversion to a mixture of unchanged ( I O U )
and the bistosylate ( 1 0 ~(colorless
)
needles, m. p. 127-128 C;
6Y41 (1971).
[2] I . . liiyrlr a n d E. Goldschniirr. Angew. Chem. 85. 824 (1973): Angew.
Chem internal. Edit. 1.767 (1973). Nachr. C'hem. Techn 21. 2x2 (1973):
('hem. Ind. ( L o n d o n ) I Y 7 3 . 1072.
[3] G. Grossniunti, Ber. Deut. C h e m G e s 22, 2298 (1889).
t f .M FWIiind R WAIL Chem Rev 6Y. 103 (1969).
[4]
[S] W
i
E . Do<vii7y and W R . Rorh. Tetrahedron I K , 67 (1962).
[6] In contrast. a iiieso-niwi valence i s o m e r m i i o n is possible under mild
conditions in the saltcyl-substituted system which IS characterized by H-honding effects a n d keto-enol taittomerism 123.
[7] I . L i / . d i r z a n d J . G. Bas. Rec. Trav. Chim Pays-Bas j Y , 173 (1940).
Simple Bridged cis-Oxa- and cis-Aza-tris-a-homobenzene Systems; Synthesis and 30+37t Isomerization[.
J
By Horst Prinzbach, Shinzo Kagabu, and Hans Fritz"]
The zero-bridged cis-tris-o-homobenzene compounds (2)
(X=CHz, CHC02CH3,O; R = C 0 2 C H j , CF3, CHI) OCCUPY
a special position in that their thermolysis proceeds not cia
the usual 30+37t cleavage to ( 3 ) (6-electron process) but
cia 20-27t cleavage to ( I ) (4-electron process)"]. The hypoth.
-
. -
&
x&~
&
.R
K
R
X
Ill
Ill
R
Ill
[*] Prof Dr. H. Prtnzhach a n d Dipl.-Chem. S. Kagabu
Lehrstuhl fur Organische Chernie der Universitit
78 Freiburg, Albertstrasse 21 (Germany)
Dr. H. Fritz
C'ibd-Geigy AG. Basel (Switzerland)
[**] This work was supported by the Deutsche Forschnngsgeineinschaft
a n d the Fonds der C'hemischen Industrie.
482
A n y w . Chem. intwnai Edir.
1 Vol. 13 ( 1 9 7 4 ) No. 7
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