Lithium keten thioacetalides. Factors influencing α-versusγ-alkylation

Abstract

Alkylation of the lithium salt of the vinyl-1,3-dithian (2; R = CH₃) occurred exclusively at the α-carbon. However both α- and γ-alkylation was observed with the substrate (2; R = C₆H₅). A systematic investigation revealed that the α : γ ratio is correlated with the hardness of both the leaving group and the alkyl group of the alkylating agent. An occasionally formed side-product from the reactions of (2; R = C₆H₅) was the α,γ-dimer (11) of the anion (6; R = C₆H₅).