Cobalt-catalyzed conformationally restricted alkylarylation enables divergent access to Csp3-rich N-heterocycles

Abstract

Due to the intrinsic spatial orientation and structural novelty, Csp³-rich N-heterocycles have been recognized as increasingly sought-after scaffolds as compared to the aromatic ring-based moieties, which have generated considerable recent attention in drug discovery. Hence, we disclose a modular cobalt-catalyzed conformationally restricted alkylarylation strategy for the divergent access to Csp³-rich N-hetero(spiro)cycles. Herein, multiple effects, including radical rebound and conformational restriction, play critical roles in the stabilization of the stereospecific alkyl-cobalt-aryl intermediate. Under simple and mild reaction conditions, cobalt catalyst combines a range of polyfunctionalized cyclenyl bromides and organozinc pivalates to rapidly and reliably forge the architecturally complex Csp³-rich N-hetero(spiro)cycles (>70 examples, >20 : 1 dr), including but not limited to the [5,5]-, [5,6]-, [5,7]-, [5,12]-bicycles, tri- and tetracyclic N-heterocycles, as well as various novel N-heterospirocyclic scaffolds in one synthetic operation. Preliminary kinetic investigations suggested that the final reductive elimination might be the rate-determining step. Moreover, ample substrate scope, good functional group compatibility and facile derivatizations to the pharmaceutically active molecules show the potential applications of this technology to organic syntheses and drug discoveries in medicinal chemistry.