C(sp³)–H Insertions with Donor Rhodium Carbenoids

Key words

carbenoids - C–H insertion - cyclopropenes

Significance

The functionalization of unactivated C(sp³)–H bonds by insertion of transition-metal carbenoids is an attractive method of forming C–C bonds. However, while acceptor-substituted rhodium(II) carbenoids have been investigated, little is known on the reactivity of donor-substituted rhodium(II) carbenoids in C(sp³)–H insertions, due to the difficulty in handling the unstabilized diazo precursors. The authors report the facile generation of donor-substituted rhodium(II) carbenoids by ring opening of 3,3-dimethylcyclopropenylcarbinols, and their use in intramolecular C(sp³)–H insertions, which occur with high yield and diastereo­selectivity.

Comment

Donor-substituted rhodium carbenoids were found to trigger 1,5- and 1,6-C–H insertions with high diastereoselectivity to generate a variety of functionalized carbocycles and oxygen heterocycles, which can be subsequently ozonolyzed to the corresponding ketones. Deuterium-­labelling studies suggest that the reaction involves a stereospecific process at the carbenoid carbon atom, and occurs in a concerted fashion with a late transition state. Furthermore, the C–H insertion process is selective for only one of two diastereotopic methylene groups, which the authors exploited to access various bicyclic compounds.