A-Ketoketene dithioacetals

The copper(I)-catalyzed addition of Grignard reagents to P-(alkylthio)-a,p-unsaturated esters is the preferred protocol for substitution of the alkylthio substituent, e.g. (310 - 311),21 while potassium enolates add to a-ketoketene dithioacetals, e.g. (312 — 313), without dialkylation (Scheme 96).218b,c Further, Hanessian reports an expedient synthesis of penam (315) via intramolecular cyclization of the (3-lactam nitroalkene (314), but loss of the methylthio moiety does not occur spontaneously (Scheme 97).219... 

Carbonyl Compounds. In the case of aldehydes, only self-condensation products are obtained, whereas aliphatic ketones usually form the corresponding dithiocarboxylates or a-ketoketene dithioacetals. If cyclic ketones are used, occurrence of carbon-carbon cleavage or formation of a-ketoketene acetals depend on the steric demands of the base. Treatment of cyclohexanone with lithium 4-methyl-2,6-di-f-butylphenoxide (12) (readily obtained by treatment of the phenol with n-butyllithium) and CS2, followed by methylation, leads via the dithiocarboxylate ion (13) to the a-ketoketene dithioacetal (14) (eq 10). ... 

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