Fe-Catalyzed α-C(sp3)–H Amination of N-Heterocycles

Abstract

Nitrogen-heterocycles are privileged structures in both marketed drugs and natural products. On the other hand, C–H amination reactions furnish unconventional and straightforward approaches for the construction of C–N bonds. Yet, most of the known methods rely on precious metal catalysts. Herein we report a site-selective intermolecular C(sp3)–H amination of N-heterocycles, catalyzed by inexpensive FeCl2, which allows the functionalization of a wide range of pharmaceutically relevant cyclic amines. The C–H amination occurs site-selectively in α-position to the nitrogen atom, even when weaker C–H bonds are present, and furnishes Troc-protected aminals or amidines. The method employs the N-heterocycle as limiting reagent and is applicable to the late-stage functionalization of complex molecules. Its synthetic potential was further illustrated through the derivatization of α-aminated products and the application to a concise total synthesis of the reported structure for senobtusin. Mechanistic studies allowed to propose a plausible reaction mechanism involving a turnover-limiting Fe-nitrene generation followed by fast H atom transfer and radical rebound.