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Ethyl 2-Oxazoline-5-carboxylate from Ethyl Isocyanoacetate and Carbonyl Compounds.

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arrangement of the epidioxydihydrofurans [reactions
(2d)/(2e)] can proceed only with cleavage of an 0-0
bond. Similar activation energies (around 20 kcal/
mole) are often found for the addition to furans and
alkylfurans (Table 1). The ease of cleavage of the 0-0
bond does not appear to be strongly influenced either
by alkyl substituents on the furan ring or by the nature
of the alcohol added. The activation energy, and hence
also the reaction temperature (Fig. 4), of the alkylfurans is distinctly increased only in the absence of
polar addends when the process is carried out in tetrahydrofuran or toluene.
Asymmetrical substitution with functional groups
strongly reduces the activation energies for addition
and decomposition. The hydroperoxides of groups 2
and 3 are formed even at -90 "C and decompose well
below 0 ° C and below -20°C respectively. In the
cases of N-methylfurfurylamine and N,N-dimethylfurfurylamine, the epidioxides and hydroperoxides are
so unstable that bimolecular reactions can n o longer
occur (Fig. 4).
The frequency factors are of the expected order of
magnitude of 1014 - 101s s-* for the decomposition of
the hydroperoxides [*51, and much lower in some cases
for the epidioxides (Table 1).
The energy diagram (Fig. 6) shows the sums of the
heats of formation of all the compounds and transition
states involved in the reaction sequence (1) + (2c) +
(3 c) for furan, as found from the measured enthalpies
and activation energies. After the absorption of a
photon by the sensitizer, the oxygen is first brought
into the 1Ag state[2,48,861, which lies 22.6 kcal/mole
above the ground state. Practically no further activation energy is required for the cycloaddition to the acceptor [2,451, and 50 kcal/mole are in fact immediately
liberated. The hydroperoxide can be formed if a further 20 kcal/mole are supplied; this is so only above
[ 8 5 ] S . W . Benson, J. Amer. chem. SOC.86, 3922 (1964).
[ 8 6 ] C.S.Foore, Accounts chem. Res. I , 104 (1968).
... ..
-.
E,
furan
furan
rn
Fig. 6. Arrhenius activation energies and reaction enthalpies for the
photosensitized cycloaddition of 0 2 to furan (schemat~c).(All values in
kcalhole).
AEo = 22.6
AEi = 0.2
AH1
=
AEz = 20.0
AH,
=
AH,
=
AE,
=
21
-3O(g)
--26(liq.)
-13(g)
- 2.4(11q.)
-54(g)
-67(liq.)
-20 "C. At this temperature, however, water is eliminated with an activation energy that is also around
20 kcal/mole [reaction (3c)l. The final product is immediately formed with liberation of a further 55-60
kcal/mole.
The activation energies of the hydroperoxide formation for all the substituted furans examined are much
lower than those of the decomposition reactions. The
hydroperoxides can therefore be isolated in favorable
temperature ranges in these cases.
The stimulus for instrumental development in the field of
low-temperature photochemistry came from Professor
G . 0 . Schenck. I am grateful to him and to Prof. Dr.
0 .E. Polansky, G. von Biinau, F. Schaller, M. Barthels,
G. Lindner, and H. Siepmann for their support, valuable
advice, and stimulating discussions.
[A 752 IE]
Received: May 13, 1969
German version: Angew. Chem. 82, 306 (1970)
Translated by Express Translation Service, London
COMMUNICATIONS
Ethyl 2-Oxazoline-5-carboxylate from Ethyl
Isocyanoacetate and Carbonyl Compounds111
the other hand, not undergoing any further decomposition.
Presumably, in addition to (Z), the carbonyl adducts ( 4 ) and
the metalated oxazolines ( 5 ) are present as intermediates.
By Dieter Hoppe and Ufrich SchoUkopf[*l
Reaction with aldehydes leads almost exclusively to formation of the trans compounds, which on hydrolysis afford the
threo forms of the P-substituted serines.
As experiments with ethyl a-isocyanopropionate and formaldehyde, acetone, or benzaldehyde have shown, the method
is also applicable to a-substituted ethyl isocyanoacetates.
Ethyl 2-oxazoline-4-carboxylates(6) are readily hydrolyzed to
serines [*, 31 and are of particular interest as model substances
for the study of base-induced electrocyclic ring-opening [41.
The esters ( 6 ) , R3 = H, cannot be prepared by a method
given previously in the literaturersl for the synthesis of
oxazolines, since, under the conditions mentioned, they are
converted by ring scission into the P-substituted ethyl aformylaminoacrylates 141. They can be prepared in good
yields, however, by treating ethyl isocyanoacetate 161 ( I ) in
ethanol with carbonyl compounds (3) in presence of a small
amount of (suspended) sodium cyanide. The catalyst undergoes partial alcoholysis and thus provides a weakly basic
medium in which ( I ) is partially converted into its sodium
derivative (Z), the (alkali-labile) oxazolines (6), R3 = H, o n
300
EthyI trans-5-phenyl-Z-oxazoiine-4-carboxylafe(6r) :
A solution of ethyl isocyanoacetate 161 (4.52 g, 0.04 mole)
and benzaldehyde (4.26 g, 0.04 mole) in dry ethanol (15 ml)
is added dropwise with vigorous stirring at 15 'C to a suspension of sodium cyanide (0.25g) in dry ethanol (10 ml).
The mixture is stirred for one hour and the solvent is then
removed (water-jet vacuum, bath temp. 5 0 - 8 0 "C). The
residue is taken up in carbon tetrachloride (50 ml) and the
Angew. Chem. iniernat. Edit.
Vol. 9 (1970) 1 NO. 4
C = N-c
NaCN/C,H,OH
H ~ - C O ~ C ~ H ~
x.
(1 )
!
R
..
:y
NaO
f 3)
Rl-6-C -C 02C zH5
A 2
..
*
:c11
n',,,c=o
Na@
..?.
C = N - C H - COzC 2H5
Na"
O@N
R'#COzC2H5
K2H
(5)
1
CHOH
A
H
A
R1-!&C0zC2H5
J
RZR3
(6 )
EthyI-2-oxazoline-4-carboxylates
(61 prepared.
accessible diazomethyl compounds. Since a C-lithium atom
is replaceable by a variety of other substituents[31, we have
directed our attention toward possible routes leading from
diazo compounds t o C-lithium derivatives c41.
We have now found that ethyl lithiodiazoacetate (2) is obtained when a) diethyl mercuriobis(diazoacetate) 151 ( I ) in
tetrahydrofuran is allowed t o react at ca. -70 "C with phenylo r butyllithium or with lithium thiolates, o r b) ethyl diazoacetate (3) is metalated at -1lOOC in ether or ether/tetrahydrofuran. The lithium compound (2) is stable only below
-5O0C[61; it can be intercepted, e.g., by trialkylstannyl or
trialkylsilyl chlorides, by carbonyl compounds, or by alkyl
halides and thus be utilized in preparative work. Since method
a) is relatively involved and not without attendant danger,
owing to the poisonous nature of the mercury compounds
formed, metalation according to b) is probably the more
suitable method for preparative purposes.
H
H
H
H
H
H
H
CH3 [b]
CH3 [b]
CH3 [bl
30
40
15
-I0
0
reflu,
30
30
reflu,
25
53
55
72
15[dl
71
47
75
67
70
0.4 : 1 [cl 86
0.5
0.5
1
0.5
0.5
1
RLi
0.5
1
1
0.5
wz
Li-C-C02C2H 5
(2)
Preparation and reactions of (2).
Intercepting
reagent
Received: January 22, 1970
[Z 147a IEI
German version: Angew. Chem. 82, 290 (1970)
_ _ ~
~~
[*I Dip1.-Chem. D.
Hoppe and Prof. Dr. U. Schollkopf
Organisch-Chemisches Institut der Universitat
34 Gottingen, Windausweg 2 (Germany)
[l] Syntheses with u-Metalated Isocyanides, Part 5. - Part 4:
U.Schollkopf and D . Hoppe, Angew. Chem. 82, 253 (1970);
Angew. Chem. internat. Edit. 8, 236 (1970).
121 Cf. S . H . Pines, S. Karady, M . A . Kozlowski, and M . Sletzinger, J. org. Chemistry 33, 1762 (1968); D. F. Elliot, J. chem.
SOC.(London) 1949, 589; J . W. Cornforth in R . C . Elderfield:
Heterocyclic Compounds. Wiley, New York 1957, Vol. 5,
p. 377ff.; U.Schollkopf and D. Hoppe, unpublished.
[3] For conversion into cysteine derivatives, see E . M . Fry,
J. org. Chemistry I S , 438 (1950); for conversion into cycloserines, see C . H . Stammer, A . N . Wilson, C. F. Spencer, F. W.
Bachelor, F. W . Holly, and K. Folkers, J. Amer. chem. SOC.79,
3236 (1957).
[41 Cf. U. Schollkopf, F. Gerhart, and R . Schroder, Angew.
Chem. 81, 701 (1969); Angew. Chem. internat. Edit. 8, 672
(1969).
151 F. Gerhartand U.Schollkopf,Tetrahedron Letters1968,6231.
161 I. Ugi, U. Fetzer, U. Eholzer, H. Knupfer, and K. Offermann, Angew. Chem. 77, 492 (1965); Angew. Chem. internat.
Edit. 4 , 472 (1965).
Ethyl Lithiodiazoacetate111
By Ulrich Schollkopf and Hubert Frasnelli[*]
In spite of the extensive work that has been carried out in
diazo chemistry (21 there is still a lack of methods available
for exchange of ligands attached t o the carbon atom of readily
1 No. 4
Interception
product
Yield (%)
in m iod
a
b
I5
52
-
resulting solution allowed t o stand for 30mins at O°C,
filtered, and the filtrate fractionated. 6.3 g (72%) of
b.p. 112 'C/0.2 torr (according t o the N M R spectrum > 95 %
truns form), is obtained [NMR spectrum (CC14): =CH, T =
3.1 (d, J = 2 Hz); IR spectrum (film): 1620cm-1 (vC=N),
1735 cm-1 (vCO)].
Angew. Chem. internat. Edit. f Vol. 9 (1970)
- RZHU
>10:1
>20: 1
>10:1
>lo: 1
[a] HCHO used as paraformaldehyde.
[b] With ethyl a-isocyanopropionate.
[cl cis and trans refer to ethoxycarbonyl and phenyl.
[d] Polymerizes on distillation; crude yield higher.
.
a
$;'z
H g(-C-C02C2H , )2
CH2=CH-CHzI
CsHsCHO
cyclohexanone
ethyl trimethylsilyldiazoacetate
ethyl trimethylsilyldiazoacetate
ethyl trimethylsilyldiazoacetate
ethyl trimethylsilyldiazoacetate
ethyl tributylstannyldiazoacetate
ethyl benzoyldiazoacetate
ethyI 2-diazopropionate
ethyl 2-diazo4-pentenoate
ethyl 2-diazo-3hydroxy-3-phenylpropionate
ethyl 2-diazo-2-( 1hydroxycyclohexy1)acetate
ethyl 2-diazo-3hydroxy-3-phenylbutyrate
47
40
25
61
50
20
45
35
45
41
62
50
Ethyl 2-diazo-3-hydroxy-3-phenylpropionute
A solution containing 47 mmoles of butyllithium (21.5ml of
a 2.2 M solution in pentane) precooled t o -70 OC is added
dropwise at -110OC t o a solution of ethyl diazoacetate
(5.47 g, 47 mmoles) in ether (150 ml) and tetrahydrofuran
(50 ml) over a period of 30 min. A solution of benzaldehyde
(5 g, 47 mmoles) in tetrahydrofuran (30 ml) which has been
cooled t o -70 OC is then added dropwise at -110 OC and the
reaction mixture is allowed to warm t o -25 'C, whereupon a
solution of glacial acetic acid (2.85 g, 47 mrnoles) in tetrahydrofuran (30 ml) that has been cooled t o -7OOC is also
added. On reaching room temperature, the solution is filtered
and the solvent removed under water-pump vacuum (rotary
evaporator, 30 "C).The residue is taken up in 500 ml of light
petroleum (b.p. 4 S 5 0 "C) and shaken with cu. 1 g of active
charcoal. After filtration the solvent is removed under waterpump vacuum. There remained 4.3 g (41 %) of crude ethyl
2-diazo-3-hydroxy-3-phenylpropionate[IR spectrum (film):
3500 (vOH), 2100 ( v N ~ ) ,1680 (vC0) cm-1; NMR spectrum
301
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oxazoline, carbonyl, isocyanoacetic, compounds, carboxylase, ethyl
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