An Improved Synthesis of Procyanidin Dimers: Regio‐ and Stereocontrol of the Interflavan Bond

Abstract

AbstractA direct and general synthesis of procyanidin dimers B1, B2, B3 and B4 (10a–d) is presented. The approach is based on the stoichiometric coupling of two protected monomeric units (the nucleophilic 2a–b and electrophilic 4a–b partners) and deals with the regio‐ and stereocontrol of the C4–C8 interflavan bond as well as the control of the degree of oligomerization. The synthesis involves a five‐step pathway starting from the native catechin (1a) or epicatechin (1b) to the fully deprotected dimers 10a–d. Furthermore, the process appears to be iterative as the coupling intermediates 9a–d themselves can be readily used in further selective syntheses of trimers or higher oligomers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)