Intramolecular cyclization of allylsilanes in the synthesis of guaian-8,12-olide. Stereoselective formation of trans- and cis-fused methylenelactones
Abstract
One-step formation of guaian-8,12-olide derivatives, α-methylene-γ-lactones fused to a perhydroazulene carbon framework with various stereochemistries, were performed from monocyclic compounds via intramolecular cyclization of ω-formyl-α-trimethylsilylmethyl-α,β-unsaturated esters. Stereochemical features of both Lewis acid- and fluoride-promoted cyclizations are discussed.