Synthesis of the spirofungin B core by a reductive cyclization strategy.

[reaction: see text] A reductive decyanation approach to the synthesis of the core of spirofungin B has been developed. Spirofungin B has only one anomeric stabilization in the spiroacetal and was isolated along with its spiroacetal epimer, spirofungin A. The cyclization precursor was constructed from readily available starting materials. The reductive cyclization reaction was both efficient and stereoselective. The reductive cyclization strategy to spiroacetals is convergent and effective.