Carbon Quaternization of Redox Active Esters and Olefins via Decarboxylative Coupling
The synthesis of quaternary carbons often requires numerous steps and complex conditions or harsh reagents that act on heavily engineered substrates. This is largely a consequence of relying exclusively on conventional polar-bond based retrosynthetic disconnections that in turn require multiple functional group interconversions, redox manipulations, and protecting group chemistry. In fact, the presence of a quaternary center even in seemingly trivial structures can dominate the practitioner's entire retrosynthetic plan (referred to by Corey as a “keying element”). Here we report a simple catalyst and minimal reagents that convert two types of feedstock chemicals—carboxylic acids and olefins—into tetrasubstituted carbons via quaternization of radical intermediates. An iron porphyrin catalyst activates each substrate by electron transfer or hydrogen atom transfer then combines the fragments by an SH2 reaction. This cross-coupling reduces the synthetic burden to procure numerous quaternary carbon-containing materials from simple chemical feedstocks.