Synthesis of tetrahydrodicranenone B

Abstract

The naturally occurring cyclopentenone, tetrahydrodicranenone B (1J), has been synthesized from the cyclopentenone (3), prepared by Birch reduction/alkylation of 6-methoxyindanone followed by ozonolysis of the dihydroindanone (2). The lower side chain was elongated by selective addition of a five-carbon Grignard reagent to the aldehyde (6), obtained from the ester (3), to give the alcohol (7). The alcohol (7) could also be prepared from the 7-methoxyindanone (14), in which all the carbons of the lower side chain are already present, by a similar reductive alkylation/ozonolysis sequence (Scheme 3). The alcohol (7) was converted into the natural product by radical deoxygenation, followed by functional group manipulation.