Organolithium reagents, reaction with enol acetates

Enolizable A -trimethylsilylaldimines can be generated in situ by the addition of organolithium reagents to bis(trimethylsilyl)formamide. These undergo addition reactions with enolates to form 3-lactams. Phosphonium salts used in catalytic amounts promote the reaction between aryl aldimines and silylketene acetals to form 3-amino esters. Mannich bases with N-2-hydroxyethyl-N-methyl substitution are prepared by the reaction of the iminium salt synthon, 3-methyl-1,3-oxazolidine, with enol silanes in the presence of chloromethylsilanes. ... 

The reactions of organolithium, -magnesium, -zinc, -copper, and -titanium reagents with aldehydes, ketones, acetals, imines and hydrazones will be described in this section. The reactions of enolates and enamines will be subsequently examined ( 6.8 to 6.10). 

Enoxysilacyclobutanes. These compounds can be prepared by Wurtz coupling of 3-chloropropyltrichlorosiIane with Mg in ether. Introduction of one alkyl group is accomplished by reaction with an organolithium reagent, and the silyl chloride can then be used for the formation of silyl enol ethers. Such 0-silyl ketene acetals are extremely reactive in aldol condensations with aldehydes without catalysts. The reaction is syn-selective. An asymmetric version uses silyl ketene acetals bearing a chiral Si-alkoxy (e.g., 8-phenylmenthoxy) group instead of an alkyl substituent. 

Unsaturated valerolactones (109) can be prepared in good yield from a-(n-butylthiomethylene)cyclohexanones by reaction with acetate enolates, followed by desulphurization and addition of an organolithium reagent (Scheme 22). ... 

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