9906 J. Am. Chem. Soc., Vol. 118, No. 41, 1996
Zhu and Espenson
be kept in mind.] The methylrhenium trioxide was synthesized from
dirhenium heptoxide and tetramethyl tin in the presence of perfluoro-
glutaric anhydride.2-4 Methylene chloride was first purified57 and stored
under argon in an amber bottle over molecular sieves. Anhydrous
benzene, ethyl diazoacetate, and all of the substrates were purchased
commercially. Their purity was checked by GC-MS.
Scheme 5
For these and other previously-known materials, the spectroscopic
parameters and other analytical data are given in the Supporting
Information.
General Procedures: (1) r-Alkoxy Ethyl Esters. The alcohol (54
mmol) and MTO (50 mg, 0.2 mmol) were dissolved in 100 mL of dry
benzene (usually) or methylene chloride in a three-necked round-bottom
flask. Ethyl diazoacetate (50 mmol) was added dropwise at room
temperature. After two days, during which time the reaction was
monitored by GC-MS, the product was recovered by vacuum distilla-
tion. The products were identified by comparison to literature
data.27,58-60
Scheme 6
(2) N-Substituted Glycine Ethyl Esters. The first method was the
same as in (1). Alternatively, MTO (0.2 mmol) was dissolved in the
amine (54 mmol) under dry argon in a three-necked round-bottom flask.
The ethyl diazoacetate (50 mmol) was added dropwise at room
temperature; with this method the reactions were complete within 1 h,
it being much faster here where no solvent diluent was used. The
products were identified, in comparison with literature data.21,27,58,59,61,62
(3) r-Thio Ethyl Esters. The first method under (1) was used,
except that the reaction was allowed to proceed for 3 days before
isolation of the product by vacuum distillation. Alternatively, the MTO
(0.2 mmol) was dissolved in the thiol (54 mmol) under dry argon in a
three-necked round-bottom flask. The EDA (50 mmol) was added
dropwise with vigorous stirring; this highly exothermic (caution!)
reaction was complete within a few minutes. This procedure can
equally well be carried out in the reverse order: the thiol may be added
dropwise into a solution of MTO in EDA. The products were identified
by comparison with data in the literature.27,59,63-65
epoxides. This reaction yields the oxalic acid monoethyl ester,
and may occur as follows:
(14)
(4) Aziridines. The imine (35 mmol, prepared as in (7)) and MTO
(250 mg, 1 mmol) were dissolved in 100 mL of dry benzene in a three-
necked round-bottom flask fitted with a water-cooled condenser, flushed
with dry argon or nitrogen for ca. 10 min, and maintained at ca. 60 °C.
Ethyl diazoacetate (30 mmol) was added dropwise with stirring. After
the addition was complete, stirring was continued another 4-6 h, during
which time the reaction was monitored by GC-MS. Finally, the mixture
was cooled to room temperature and the solvent removed under vacuum.
The aziridines were isolated by vacuum distillation and purified on a
silica gel column from which they were eluted with benzene.
The products were identified by spectroscopic and microanalytical
data,30,64-66 as presented in the supporting information.
As written, this reaction produces an aldehyde. We have shown
in independent experiments that with cis-stilbene oxide benz-
aldehyde forms the carboxylic acid in an MTO-catalyzed
reaction. For example, the reaction of cis-stilbene oxide,
benzaldehyde, and MTO (in 20:2:1 ratio with 14 mg of MTO
in 1 mL of CDCl3) gave 90% benzoic acid and stilbene in 20
h.
(5) Epoxides. MTO (50 mg, 0.2 mmol) was dissolved in 20 mL of
the aldehyde or ketone. The flask was sealed with a rubber stopper,
and the solution brought to 50-60 °C. Ethyl diazoacetate (5 mL, 48
mmol) was added dropwise while the pressure was relieved occasion-
ally. After 3 days, during which time the reaction was monitored with
GC-MS, the product was isolated by vacuum distillation. The products
were identified spectroscopically in comparison with data from the
literature.66-71
The reactions of the organic azides may also be explained in
terms of the proposed intermediate AN. Species 10 would
presumably be formed from MTO by the analogous process,
and would be subject to nucleophilic attack, leading to the
products observed, Scheme 5.
The conversion of azibenzil to benzil by MTO-catalyzed
oxygen transfer from an epoxide provides further proof for the
suggested intermediate AC, because no metal carbenes have been
reported to react with epoxides to form carbonyl compounds.
Thus we propose a sequence in which AC′, analogous to AC
from ethyl diazoacetate, is formed first from MTO and azibenzil.
It then reacts further to form benzil and methylrhenium dioxide.
The latter species abstracts oxygen from an epoxide; this is a
known reaction reported in our earlier work.8 The sequence of
steps is diagrammed in Scheme 6.
(57) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Butterworth-Heinemann: Oxford, 1988.
(58) Bryson, A.; Davies, N. R.; Serjeant, E. P. J. Am. Chem. Soc. 1963,
85, 1933.
(59) NIST MS Library from Magnum; Finnegan MAT: San Jose, CA,
1990.
(60) Kadentsev, V. I.; Chizhov, O. S.; Yanovskaya, L. A.; Kucherov,
V. F. IsV 1971, 10, 2207.
(61) Munshi, A. A.; Trivedi, J. P. J. Ind. Chem. Soc. 1966, 43, 277.
(62) Lemont, B. K.; Dhawan, D. J. Pharm. Sci. 1962, 51, 1058.
(63) Chauveau, A.; Mathis-Noel, R. Ann. Fac. Sci. UniV. Toulouse Sci.
Math. Sci. Phys. 1963, 25, 147.
Experimental Section
Materials. Butyl, hexyl,55 and phenyl56 azides were prepared
according to the literature. [CAUTION: Although we encountered
no difficulties, the potentially explosive nature of organic azides should
(64) Coti, L. Boll. Chim. Farm. 1967, 106, 47.
(65) Uyeda, Y.; Reid, E. E. J. Am. Chem. Soc. 1920, 42, 2388.
(66) Vandenbroucke, W.; Anteunis, M.; DeBruyn, A. Bull. Soc. Chim.
Belg. 1969, 78, 229.
(54) Gambarotta, S.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. Orga-
nometallics 1986, 5.
(55) Boyer, J. H.; Hamer, J. J. Am. Chem. Soc. 1955, 77, 950.
(56) Smith, P. A. S.; Brown, B. B. J. Am. Chem. Soc. 1951, 73, 2438.
(67) Roux-Schmitt, M. C.; Seyden-Penne, J. Tetrahedron 1972, 28, 4695.
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