Multiple chirality transfers in the enantioselective synthesis of 11-O-debenzoyltashironin.: Chiroptical analysis of the key cascade

The mechanism of the cascade oxidative dearomatization-transannular Diels-Alder was investigated in the context of an asymmetric route to (-)-11-O-debenzoyltashironin. Although the oxidative dearomatization provides two acetal intermediates, the transannular Diels-Alder proceeds spontaneously from only one of the acetal isomers. Access to enantioenriched tetracyclic adduct was gained through the use of optically active allene. (C) 2008 Elsevier Ltd. All rights reserved.