Abstract
The bicyclobutylidenes 2 and 5 have been rearranged to the bicyclooctenes 3 and 6, respectively, and further transformed to the tricyclic ketones 16 and 21, respectively, as known precursors of (±)-ceratopicanol ( 4) and (±)-hirsutene ( 7). For the cyclopentane annelation, a [3+2]cycloaddition with cyclopropane-1,1-dicarboxylic acid ester, followed by an alkaline hydrolysis and an oxidative decarboxylation of the diacids formed was used ( 3-8-14-16, 6-18-20-21). The structures of the cycloadduct 9, the diacid 15 and the ketone 17 followed from an X ray analysis of the ditosylate 13, itself obtained by reduction and tosylation ( 9-12-13). The new syntheses of 16 and 21 represent short entries to 4 and 7.
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