Dealkanative main group couplings across the peri-gap

Abstract

Here, we highlight the ability of peri-substitution chemistry to promote a series of unique P–P/P–As coupling reactions, which proceed with concomitant C–H bond formation. This dealkanative reactivity represents an interesting and unexpected expansion to the established family of main-group dehydrocoupling reactions. These transformations are exceptionally clean, proceeding essentially quantitatively at relatively low temperatures (70–140 °C), with 100% diastereoselectivity in the products. The reaction appears to be radical in nature, with the addition of small quantities of a radical initiator (azobisisobutyronitrile) increasing the rate dramatically, as well as altering the apparent order of reaction. DFT calculations suggest that the reaction involves dissociation of a phosphorus centred radical (stabilised by the peri-backbone) to the P–P coupled product and a free propyl radical, which carries the chain. This unusual reaction demonstrates the powerful effect that geometric constraints, in this case a rigid scaffold, can have on the reactivity of main group species; an area of research that is gaining increasing prominence in recent years.