3790
Gas-Phase Pyrolysis of Methyl Diazomalonate Wolff Rearrangement of Biscarbomethoxycarbene' Sir; Until rather recently, the Wolff rearrangement of carboalkoxycarbenes was a neglected reaction. * Attention has now turned to this process and mechanistic information has been forthcoming from Schenck and Ritter,3 Westheimer and C O W O T ~ ~ ~ and S , ~ 'most ~ reThe cently from Strausz and his importance of oxirenes in the Wolff rearrangement of diazoacetates has been stresseda~lo~l and intermediate alkoxyketenes have been t r a ~ p e d . ~So far, however, the Wolff rearrangement of carboalkoxycarbenes has been observed only on photolysis, and the absence of the thermal reaction has been thrice noted.g We report here the preliminary results of our investigations of the gas-phase pyrolysis of methyl diazomalonate and demonstrate that the thermal Wolff rearrangement is an important process. Pyrolyses were conducted under vacuum by evaporating methyl diazomalonate through an empty quartz tube into a trap cooled to 77°K. Product analysis was by a combination of nmr spectroscopy and gas chromatography. The products of the pyrolysis were not interconverted under the reaction conditions. At temperatures up to 260" methyl diazomalonate was recovered unchanged. At 280" methyl acrylate was by far the major product, although small amounts of methyl acetate and methyl vinyl ether were also visible. The source of the acrylate is very likely a reaction so far undetected in solution, insertion into the carbon-hydrogen bond of the U-methyl group to give the p-lactone 1, which cleaves to give carbon dioxide and methyl acrylate. Cleavages of /3-lactones at elevated temperatures are known, and stable lactones have been isolated from irradiations of tert-butyl diazo-
acetate and tert-amyl diazoacetate16 as well as from the thiobenzophenone-sensitized decomposition of ethyl diazomalonate. Lactams have been made from diazoamides as well. la At higher temperatures methyl pyruvate appeared along with methyl acetate, and methyl vinyl ether became a major product. We attribute the formation of the ether to Wolff rearrangement to ketene 2, followed by loss of carbon monoxide to give the new carbene 3. Self-insertion followed by loss of carbon dioxide gives methyl vinyl ether. Again the easiest reaction for the carbene seems to be intramolecular carbon-hydrogen insertion. By 400" methyl acetate and methyl
-
CHjOOC,
,c:
CH,OOC
CHjOOC,
-
,c=c=o
CHBO
J
pyruvate were present in substantial amounts. The overall yield of products varies little from 420 to 540" and is ca. 65% based on carbene. Table I gives the product composition as a function of temperature. Table I. Variation of Products Pyrolysis with Temperature
(z) of Methyl Diazomalonate
Temp, "C
Methyl pyruvate
Methyl acrylate
Methyl acetate
280 300 330 360 390 420 450 480 500 540
0 0 6 3 7 1 6 1 6 8
92
3 8 12
12 51 38 29
32 35 29 30 30
Methyl vinyl ether 5 20 31 52 56 52 51 54 51 53
1 8 8 8 9 8 9
1
CH,OOC, CH-CH, (1) Generous support of this work by the National Science Foundation through Grant No. GP-12759 is gratefully acknowledged. (2) For reviews, see W. E. Bachman and W. S . Struve, Org. R e u c f . , 1, 38 (1942); F. Weygand and H . S . Bcstmann, Newer Mefhods Prep. O r g . Chem., 3, 451 (1964). (3) G. 0. Schenck and A. Ritter, Tefruhedron L e t f . , 3189 (1968). (4) J. Shafer, P. Baronowsky, R. Lausen, F. Finn, and F. H . Westlicimer, J . Biol. Chem., 241, 421 (1965). ( 5 ) H . Chaimovich, R . J. Vaughan, and F. H. Westheimer, J . Amer. Chem. Soc., 90, 4088 (1968). (6) 0 . P. Strausz, T. DoMinh, and H. E. Gunning, ibid., 90, 1660 (1 968). (7) I . G . Csizmadia, J . Font, and 0. P. Strausz, ibid., 90, 7361 (1968). ( 8 ) T. DoMinh, 0. P. Strausz, and H. E. Gunning, ibid., 91, 1261 (1969). (9) T. DoMinh and 0. P. Strausz, ibid., 92, 1766 (1970). (10) D. E . Thornton, R. I
