Enolates by Miscellaneous Methods

The decomposition of THF with n-butyllithium is a very efficient method for producing the lithium enolate of acetaldehyde. The reaction is easily rationalized by assuming deprotonation in the a-oxygen position, followed by a [2-1-3] cycloreversion of the anion 186. The enolate 187 resulting under concomitant liberation of ethylene has been trapped by different electrophiles among them the silylation proves the existence of the enolate [176]. 

In summary, this chapter on the preparation of enolates may show that a variety of reliable methods with nearly perfect control of regiochemistry, highly developed diastereoselectivity for both cis- and tra/is-configured enolates, and even enantioselectivity are available today. It will be outlined in Chapters 4 and 5 that these methods are the fundament of the enolates successful applications in asymmetric syntheses. 

For - at the corresponding time - comprehensive and highly informative overviews, see (a) House, H.O. (1972) Modern Synthetic Reactions, 

Negishi, E. (1980) Organometallics in Organic Synthesis, vol. 1, John Ydley Sons, Inc., New York, pp. 41-44. 

For a short, early overview, see Lappert, M.F., Power, P.P., Sanger, A.R., and Srivastava, R.C. (1980) Metaland Metalloid Amides. Synthesis, Structures, 

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Alkali Metal Enolates from Enol Acetates and Silyl Eru>l Ethers 1.423 Alkali Metal Enolates by Miscellaneous Methods... 

Miscellaneous Reactions. Trimethylsilyldiazomethane converts acid- and base-sensitive maleic anhydride derivatives into the corresponding bis(methyl esters) (eq 70). Terminal silyl enol ethers are conveniently prepared from aldehydes by first treating the carbonyl compound with TMSC(Li)N2, followed sequentially by methanol and Rh2(OAc)4 (eq 71). The method works well with base-sensitive substrates and is superior to the attempted regioselective deprotonation/O-silylation of the corresponding methyl ketone. ... 

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