Stannyl cyclopropanes by diastereoselective cyclopropanations with (tributylstannyl)-diazoacetate esters catalyzed by Cu(I)N-heterocyclic carbene

Catalyzed cyclopropanations of alkenes with Bu3SnC(=N2)CO2R (R = Et, t-Bu) have been achieved in good yield with excellent diastereoselectivity to make stannyl cyclopropanes having two or three stereocenters, one of which is quaternary.