Rate-Accelerating Effect by the Neighboring-Group Participation of Protecting Groups in the Dehydrative Cyclization of 1,3,5-Triketones.

[摘要]：Neighboring-group participation of an acyl protecting group efficiently promotes the Bronsted acid-catalyzed dehydrative cyclization of 1,3,5-triketones, e.g. (pivaloyloxy)trimethylnonanetrione I (R = Me3CCO), to g-pyrones, e.g. [(pivaloyloxy)ethyl]pyranone II, whereas a bulky silyloxy group in the b-position of a triketone, e.g. I (R = Me3CSiPh2) retards cyclization. This reaction provides an efficient synthetic route for a common intermediate for the synthesis of g-pyrone-contg. bioactive natural products.

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