A reductive cyclization approach to attenol A.

A reductive cyclization strategy was applied to the synthesis of attenol A. This nontraditional approach to the spiroacetal structure illustrated several advantages of the reductive cyclization methodology. The attenol A core was formed in a carbon-carbon bond coupling that gave rise to a previously inaccessible spiroacetal epimer, a new method to synthesize thioketene acetals from a phenyl sulfone was realized, and the configurational stability of a nonanomeric spiroacetal was evaluated. A minor byproduct in the reductive cyclization reaction was identified that for the first time allowed direct evaluation of the stereoselectivity in a reductive cyclization of a dialkyloxy alkyllithium reagent.