Trimethylenemethane for Everyone: Convenient Preparation of the Nakamura‐Yamago 1,3‐Dipolar Reagent and an Effective Oxidative Transformation of Ketene Acetals

Abstract A convenient route to the Nakamura‐Yamago methylenecyclopropane (MCP) precursor 1 to oxygen‐stabilized, singlet trimethylenemethane (TMM) is reported, which avoids the hurdles of the original preparation procedure. An effective oxidation protocol is also introduced for converting the sensitive ketene acetals (KAs) from 1,3‐dipolar cycloaddition of 1 to electron‐poor olefins, into the corresponding α‐hydroxyesters. The method, based on the use of dimethyldioxirane (DMDO) in acetone, affords fair to good yields (23–81%) for a number of KAs endowed with ketone, ester, or imide functional groups, as well as additional C─C double bonds. The utility of the protocol is further exemplified by the diastereoselective preparation of the Rokach‐Galano‐Durand bicyclic lactone rac‐ 18 , one of the most versatile building‐blocks for the synthesis of isoprostanoidic derivatives.