Chromium‐Thiophene‐salen‐Based Polymers for Heterogeneous Asymmetric Hetero‐Diels–Alder Reactions

Abstract

AbstractNew chiral thiophene‐salen ligands have been synthesized and the corresponding chromium complexes proved to beefficient catalysts for promoting asymmetric hetero‐Diels–Alder reactions with good activities and high enantioselectivities (up to 88 % ee). These complexes were successfully electropolymerized to give chiral polymers as insoluble powders for use in asymmetric heterogeneous catalysis. When engaged in successive hetero‐Diels–Alder reactions, they afforded the expected products in high yield and enantioselectivity showing no loss of efficiency for up to 15 cycles. A chiral chromium‐salen‐thiophene polymer was also successfully used in a multi‐substrate procedure in which a new, structurally different aldehyde was introduced for each reuse to afford the desired pyranone in its pure form. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)