Summary:. 4 stereospecific ring-expansion synthesis of trans-fused cy-methylene y-lactones can be accomplished in excellent yield through the sequence of carbene addition of tert- butyl diazopyruvate to cyclic dienes, inverse Wittig condensation to give a tert-butyl ester substituted transdivinylcyclopropane, and acid-catalyzed cleavage of the cyclopropane ring
