Enantioenriched Synthesis of Cyclopropenes with a Quaternary Stereocenter, Versatile Building Blocks

Ir(salen) complexes were found to catalyze enantioselective cyclopropenation efficiently. Cyclopropenation can be carried out using either a donor/acceptor- or an acceptor/acceptor-substituted diazo compound such as alpha-aryl-alpha-diazoacetates, alpha-phenyl-alpha-diazophosphonate, 2,2,2-trifluoro-1-phenyl-1-diazoethane, and alpha-cyano-alpha-diazoacetamide as carbenoid precursors. The reactions provide highly enantioenriched cyclopropenes (84-98% ee) with a functionalized quaternary carbon as versatile building blocks.