α-Thio-substituted ketones as precursors of olefins via oxathiolanes: benzyl as protecting group

Abstract

The feasibility of a regiospecific synthesis of tetrasubstituted olefins starting from protected α-thiol substituted ketones has been demonstrated by three examples. The approach (see Scheme) involves: S-activated alkylation (i), carbonyl addition of an organometallic reagent (ii), deprotection (iii), formation of a 2-phenyloxathiolane (iv), and base-promoted cycloelimination (v). An unsatisfactory feature is the lack of stereochemical control in step (ii).

An attempt to telescope steps (iii) and (iv) by sequential Pummerer reaction–cyclisation at the β-benzylthio alcohol stage was unsuccessful.