Total Synthesis and Configurational Validation of (+)-Violapyrone C.

Gold(I)-catalyzed intramolecular 6-endo-dig cyclization of tert-butyl ynoates afforded α-pyrone cores of violapyrones. Moreover, this reaction was successfully applied to the stereospecific syntheses of (+)- and (–)-violapyrone C, which allowed the absolute configuration of natural (+)-violapyrone C to be assigned by comparison of the optical rotations. This first total synthesis, which proceeded in 22 % yield over 10 steps from (S)-(–)-2-methylbutanol, features silver(I) oxide promoted monobenzylation of 1,4-butanediol, Wittig olefination, Claisen condensation, Corey–Fuchs reaction, and gold(I)-catalyzed α-pyrone synthesis.

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