Synthesis and reactivity of lithiated γ-functionalised ketene dithioacetals. Generation of a flexible β-lithioacrylate equivalent

Abstract

The synthesis of 1,1,3-tris(phenylthio)prop-1-ene (8) is described. Anion (9), obtained by deprotonation of (8) with lithium di-isopropylamide, reacts with a wide range of electrophiles to give the γ-substituted adducts (10) exclusively. The relative importance of steric and electronic effects in determining the high γ-regioselectivity observed for (9) have been evaluated using a series of related ketene dithioacetals (12)–(15), and (17). The equivalence of anion (9) to a β-lithioacrylate has been illustrated by constructing a series of a,β-unsaturated γ- and δ-lactones and a short synthesis of (±)eldanolide is also described. Anion (9) undergoes a facile dimerisation in the presence of oxygen to give dimer (20) and a mechanistic rationale for this observation is presented.