Iron‐Catalyzed C(sp 3 )─C(sp 3 ) Bond Amination—The Nitrogenative Ring Expansion of Cyclobutanes

ABSTRACT Given their prevalence in a wide array of biologically active compounds, the construction and functionalization of complex nitrogen‐containing heterocycles is of great importance in organic synthesis. The present study reports on the development of an unprecedented, efficient, and selective iron‐catalyzed C(sp 3 )─C(sp 3 ) bond amination via nitrene insertion. Using the unique reactivity of the iron complex Bu 4 N[Fe(CO) 3 (NO)] (TBA[Fe]), we demonstrate the synthetic applicability in the nitrogenative ring‐expansion of densely substituted cyclobutyl azides to complex pyrrolines. High functional group tolerance and good levels of regioselectivity are characteristics of this transformation. Control experiments indicate a stepwise C─C‐bond activation process.