Lewis acid-promoted intramolecular cyclization of -prenylated chalcones: application to first total synthesis of (±) involucrasin C and its novel analogues.

This study presents a refinement of a synthetic protocol for the diastereoselective intramolecular ene-type cyclization of -prenylated chalcones using ZnCl, leading to the corresponding tertiary alcohols sans the undesired alkene by-product. While InCl·4HO offers the best yield, ZnCl with slightly diminished yield provides a cheaper alternative. To assess diastereoselectivity, the prenyl group was replaced with a cinnamyl moiety, forming a third consecutive chiral center as a single diastereomer. Additionally, total synthesis of (±) involucrasin C, along with the synthesis of several structurally related novel analogues, is presented in this work.