Addition of alkenes to tricarbonyl(vinylketene)iron(o) complexes and the synthesis of cyclopropanes

The tricarbonyl(vinylketene)iron(o) complex 1 reacts with electron-poor alkenes to give decarbonylated adducts 3 and these are oxidised to tetrasubstituted cyclopropanes 4 using CAN; an X-ray crystal structure analysis of the adduct formed from 1 and dimethyl fumarate define its relative stereochemistry.