Chemoselective Intramolecular Carbonyl Ylide Formation through Electronically Differentiated Malonate Diesters

A method for chemoselective carbonyl ylide formation utilizing the Rh­(II) catalyzed decomposition of electronically differentiated diazo malonates is disclosed. Treatment of ethyl, trifluoro ethyl diazo malonate with a Rh­(II) catalyst selectively forms a carbonyl ylide from the relatively electron rich ethyl ester. This carbonyl ylide can be trapped by various alkynes giving highly functionalized oxabicyclic compounds in a chemo-, regio-, and diastereoselective fashion.