Role of <i>Ortho</i>-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.