Construction of the ingenane core using an Fe(III) or Ti(IV) Lewis acid-catalyzed intramolecular [6+4] cycloaddition

A facile entry into the ingenane core using a Lewis acid-catalyzed intramolecular [6+4] cycloaddition has been developed. Ti(IV)- and Fe(III)-based Lewis acids were found to mediate the higher order cycloaddition in good to excellent yield at room temperature. Chiral Ti(IV) Lewis acids were found to induce modest asymmetry in the resultant [6+4] cycloadducts. (C) 2002 Elsevier Science Ltd. All rights reserved.