Atropo-Enantioselective Synthesis of the Natural Bicoumarin (+)-Isokotanin A via a Configurationally Stable Biaryl Lactone

The atropo-enantioselective total synthesis of the axially chiral bicoumarin (+)-isokotanin A (1) is described. Key steps were the formation of a configurationally stable seven-membered biaryl lactone and its kinetic resolution by atroposelective ring cleavage. The previous assignment of the absolute configuration of (+)-isokotanin A (1) (and its synthetic precursors) was confirmed by quantum chemical CD calculations. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)