Cobalt(II)‐Catalyzed Asymmetric Olefin Cyclopropanation with α‐Ketodiazoacetates

Porphyrin and Co.: The cobalt(II) complex 1 is an effective metalloradical catalyst for cyclopropanation of alkenes with α-acetodiazoacetates at room temperature to yield E-1,1-cyclopropaneketoesters in high yields with both high diastereo- and enantioselectivities. Epimerization of the resulting enantioenriched E diastereoisomers into the corresponding Z isomers with retention of the enantiopurity is promoted by iodide.