L-Proline-Catalyzed Direct Intermolecular Asymmetric Aldol Reactions of 1-Phenylthiocycloalkyl Carboxaldehydes with Ketones. Easy Access to Spiro- and Fused-Cyclobutyl Tetrahydrofurans and Cyclopentanones

Abstract

[reaction: see text] Acid-catalyzed ring expansion of chiral cyclopropyl and cyclobutyl derivatives for the synthesis of carbo- and heterocyclic compounds is reported. The starting materials have been successfully prepared by l-proline-catalyzed direct asymmetric aldol reactions of 1-phenylthiocycloalkyl carboxaldehydes with ketones.