Exploration of a KI-catalyzed oxidation system for direct construction of bispyrrolidino[2,3-b]indolines and the total synthesis of (+)-WIN 64821.

A facile and environmentally benign KI(cat.)/NaBO3·4H2O oxidation system has been developed for the tandem oxidative aminocyclization/coupling of tryptamines, affording a series of 3a,3a'-bispyrrolidino[2,3-b]indolines with high efficiency (up to 94% yield). This reaction features an electrophilic "I+" mechanism, which is importantly quite different from and milder than the typical radical-involving process, and can be readily amplified for the total synthesis of (+)-WIN 64821.