Low temperature carbene transfer from alkoxychromium(0) (Fischer) carbene complexes

Irradiation at low temperatures (0°C) of alkyl-, aryl- and styryl alkoxychromium(0)carbene complexes in the presence of methyl acrylate produces a mixture of diastereomeric cyclopropanes and C–H insertion derivatives. The ratio cyclopropane/C–H insertion product is independent of the reaction conditions, while the cyclopropane cis:trans ratio strongly depends on the solvent, the selectivity increasing as the polarity of the reaction solvent does.