Papyracillic acids are naturally occurring spirofused cyclic ketals, which lend themselves as attractive synthetic targets. Development of a zinc carbenoid homologation-acylation reaction was achieved in order to synthesize the spirofused ketal core in one concise step. Subsequent functionalization of the carboxyester group included a deallyation, sodium borohydride reduction, and selenide oxidation-elimination, which produced papyracillic acid B and epimers at quatenary carbon (C-4). Stereochemical assignments were determined by X-ray crystal structure analysis for several key intermediates.

Synthesis of spirofused cyclic ketals

244th National Meeting (2012)

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