Oxidative dimerization of 2-oxindoles promoted by KO(t)Bu-I₂: total synthesis of (±)-folicanthine.

A 'transition-metal-free' oxidative coupling of 2-oxindoles has been demonstrated in the presence of 1.2 equiv each of potassium tert-butoxide and iodine. The method yields a diverse range of structurally different homo- and heterodimerized 2-oxindoles bearing vicinal all-carbon quaternary centers of great synthetic importance. A radical-driven pathway has been tentatively proposed.