Two procedures for the preparation of trimethylsilyl enol ethers from aldehydes and ketones are described. Reaction of the ketone with chlorotrimethylsilane and triethylamine in dimethylformamide solution usually affords an equilibrium mixture of the trimethylsilyl enol ethers. Successive reaction of the ketone with lithium diisopropylamide and with chlorotrimethyhilane in l12-dimethoxyethane solution normally produces a mixture in which the less highly substituted enol ether (from kinetically controlled enolate formation) is the principal product. A number of representative structurally and stereochemically isomeric trimethylsilyl enol ethers have been characterized (see Table 11) and their physical properties have been studied. (1968). (5) For descriptions of the preparation of silyl enol ethers, see (a) C. R. Krager and E. G . Rochow, J . Orwnometal. Chem., 1, 476 (1964); (b) J. I. Baukov, G . S. Burlachenko, and I. F. Lutsenko, ibid., 8, 478 (1965); (c) R. J. Fessenden and J. S. Feesenden, J . Ow. Chem., 82, 3535 (1967); (d) R. Bourhis and E. Frainnet, Bull. Soe. Chim. Fr., 3552 (1967); (e) U. Schmidt and M . Schwochan, Tetrahedron Lett., 4491 (1967); (f) G. Stork and P. F. Hudrlik, J . Amer. Chem. Soc., 90, 4462, 4464 (1968). (6) For examples of the rearrangement of 2-silyl ketones to enol ethers, see (a) A. G . Brook, D . M. MacRae, and W. W.Limburg, J . Amer. Chem. Soc., 89, 5493 (1967); (b) I. F. Lutsenko, Yu. I. Baukov, 0. V. Dudukina, and E. N. Kramarova, J . Organometal. Chem., 11, 35 (1968). (8) The use of trimethylsilyl chloride as a scavenger for alkoxides has been used to advantage in the acyloin condensation. See (a) J. J. Bloomfield, Tetrahedron Lett., 587, 591 (1968); (b) G. E. Gream and 9. Worthley, ibid., 3318 (1868).

2,3-diphen.ylcyclopropenone diethyl ketal, making a reasonable allowance for the difference in temperature at which the rate measurements were made. Tropone ethylene ketal was the only compound in the series for which general acid catalysis was observed. Therefore, the boundary line between the Al mechanism and one involving general acid catalysis, in terms of carbonium ion stability, lies somewhere between pAR+ values of -0.67 and +4.7, with probability that it lies closest to the more positive figure. Thus, for general acid Catalysis of acetal hydrolysis to occur in cases where the leaving group is poor, the intermediate carbonium ion must be exceedingly stable, i.e., the bond-breaking step must be quite easy.

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The -chloro ketones, 2-chlorocyclohexanone (5), chloromethyl cyclohexyl ketone (7), and phenacyl chloride (13), have been converted to the corresponding enol acetates and trimethylsilyl enol ethers. These enol derivatives have served as precursors for the corresponding lithium -chloro enolates 6, 8, and 16 which are stable intermediates. Even the addition of copper(I) compounds or the formation of -mercuri derivatives of these enolates does not promote their decomposition to -ketocarbenes. In contrast, the -diazo derivatives 17 and 21 of acetophenone and methyl cyclohexyl ketone are readily decomposed by added copper(I) derivatives. The soluble complex, (n-BmS hCul, is an especially convenient catalyst for the decomposition of these -diazo ketones, compound 21 being rapidly decomposed in solution at 5-10°. With small amounts of this catalyst and excess olefin the norcarane derivative 22 was the major product. With an equimolar amount of this catalyst, the keto sulfide 26 (believed to arise from a sulfur ylide intermediate) became the major monomeric product.