Diastereoselective synthesis of thieno[3′,2′:4,5]cyclopenta[1,2-d][1,3]-oxazolines -: New ligands for the copper-catalyzed asymmetric conjugate addition of diethylzinc to enones

Several new ligands featuring a rigid three ring skeleton have been prepared for the first time following a modular approach. Chirality has been introduced by use of an oxazoline moiety fused with a cyclopenta[b]thiophene backbone. The efficiency and stereochemical impact of these ligands on the copper-catalyzed enantioselective addition of Et2Zn to chalcone was examined and enantiomeric excesses up to 79% were achieved using the ligand (R,R)-16 substituted with a methyl group at the cyclopenta moiety. Computational and ESI-mass spectral studies show that these new compounds behave as monodentate ligands towards Cu+. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).