Rhodium-catalyzed asymmetric intramolecular cyclopropanation of substituted allylic cyanodiazoacetates

A chiral rhodium catalyst, Rh-2[4S-(4')FBNAZ](4), was synthesized and was shown to catalyze the intramolecular cyclopropanation of substituted allylic cyanodiazoacetates. Alkenes bearing an electron-deficient substituent including carbonyl and halogens are converted into the corresponding cyclopropanes in high yields with both chiral and achiral rhodium catalysts. The cyclopropane derivatives were generated with an enantioselectivity of up to 91% ee. For the asymmetric intramolecular cyclopropanation, cis-halogen-substituted substrates afforded cyclopropanes with higher enantioselectivities than the corresponding trans diastereomers. However, only moderate enantioselectivities were observed with alkenes bearing electron -donating groups such as alkyls. The cyclopropanation of 3-substituted 2-propenyl cyanodiazoacetates was strongly influenced by steric and electronic factors arising from substituents on the alkenes. For the first time, we demonstrated that the intramolecular reaction of gem-dihaloallylic cyanodiazoacetate afforded highly functionalized gem-dihalocyclopropanes. This reaction is an appealing alternative to the addition of dihalocarbenes to alkenes for the formation of gem-dihalocyclopropanes.