Stereoselective synthesis of polyketide fragments using a novel intramolecular Claisen-like condensation/reduction sequence

Intramolecular Claisen-type cleavage of the Evans-oxazolidinone with an acetate enolate followed by reduction of the resulting ketone using a borane–amine complex yielded β-hydroxy-δ-lactones as fully functionalized polyketide precursors stereoselectively. Consequently, this reaction sequence constitutes a highly practical alternative to an acetate–aldol reaction.