Acylsilane enolates, synthesis

Both ketones and aldehydes, as well as acylsilanes can be employed as carbonyl substrates in the new p-lactone synthesis (Table). Reactions involving ketones are most conveniently carried out by adding the neat carbonyl compound to the thiol ester enolate solution. Under these conditions aliphatic aldehydes react to form substantial quantities of 2 1 adducts however, formation of these side products can be suppressed simply by slowly adding the aldehyde component as a precooled (-78°C) solution to the reaction mixture. Wide variation is also possible in the thiol ester component, although a few limitations of the method have been noted. For example, a,p-unsaturated ketones such as methyl vinyl ketone and cyclohexenone fail to yield p-lactones, and attempts to generate p-lactones with severe steric crowding have also met with limited success.3... 

Acylsilanes are versatile intermediates for carbon-carbon bond formation reactions, and may serve as precursors for the synthesis of silyl enol ethers, aldehydes, or carboxylic acids. In the presence of a base or certain nucleophiles, they undergo the Brook rearrangement, where the silyl moiety migrates from carbon to oxygen (see below in this section). 

Radical cyclization using acylsilanes is apphcable to the synthesis of cychc silyl enolates by yS-elimination of the a-siloxyalkyl radical intermediate (Scheme 10.234) [603]. 5-Bromo-5-stannyl- and 5-bromo-2-sulfonyl-alkanoylsilanes are cychzed to cyclopentanone silyl enolates with ehmination of the stannyl and sulfonyl groups. 

Review. Cirillo and Panek have reviewed progress in the chemistry of these compounds during the last two to three years (48 references). A new synthesis involves homologation of aldehydes with methoxybis(trimethylsilyl)methyllithium (1) to form enol ethers of an acylsilane (equation I). Acylsiianes can be prepared in high yield by... 

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