α,β-Unsaturated Acetals in Synthesis

Abstract

In this review some results are reported that allow the acetal group of α,β-unsaturated carbonyl derivatives to be considered not simply a protective function but also a synthetic tool for transforming aldehydes (and ketones) into a cheap and easily accessible starting material for the construction of various and more complex structures. The reported results can be grouped into three main sections: α,β-unsaturated as masked acyl anions, as precursor of dienophilic moieties, and as reagent in organometallic syntheses. In many reported examples the key reagents are polar organometallic reagents, and in particular, the bimetallic (lithium-potassium) mixed base LICKOR, which is also known as Schlossers superbase. We are not acquainted with previous reviews on these topics, and in our survey we have considered the literature later than the eighties. Keywords: unsaturated acetals, masked acyl anions, dienophilic moieties, polar organometallic reagents, (lithium-potassium) mixed base, Schlossers superbase