Dealkanative Main Group Couplings across the peri-Gap

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
(azobis­(isobutyronitrile)) increasing the rate dramatically, as well
as altering the apparent order of reaction. DFT calculations suggest
that the reaction involves dissociation of a phosphorus centered radical
(stabilized 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.