Role of ortho-substituents on rhodium-catalyzed asymmetric synthesis of β-lactones by intramolecular C-H insertions of aryldiazoacetates.

A rhodium-catalyzed asymmetric synthesis of β-lactones via intramolecular C-H insertion into the ester group of aryldiazoacetates has been developed. The β-lactones were synthesized in high yields and with high levels of diastereo- and enantioselectivity. Halo and trifluoromethyl substituents at the ortho position of the aryldiazoacetates enhance intramolecular C-H insertions over intermolecular reactions, allowing C-H insertion of even methyl C-H bonds.