Iridium‐Catalyzed Enantioselective Formal <i>meta</i> ‐Allenylation of Pyridines

Abstract

Abstract Site‐selective functionalization of pyridines is an important yet challenging transformation. Temporary dearomatization of pyridines through redox‐neutral cycloaddition has recently emerged as a reliable and attractive strategy for meta ‐functionalization of pyridines. Despite the amenability of the resulting bench‐stable cycloadduct, oxazinopyridine, to a variety of electrophilic and radical‐based reagents, its enantioselective functionalization remains unexplored. Herein, we present the first enantioselective meta ‐functionalization of pyridines through the intermediacy of oxazinopyridines. This highly enantioselective formal meta ‐allenylation of pyridines is achieved by treating the easily accessible oxazinopyridines with racemic allenylic alcohol under the combination of a catalytic amount of an Ir(I)/(P, olefin) complex and Lewis acidic Sc(OTf) 3 followed by acid‐mediated rearomatization. With oxazinopyridines derived from unsubstituted or suitably substituted pyridines, iterative 3,5‐difunctionalization is possible, which also allows for the stereodivergent synthesis of all four stereoisomers of 3,5‐bis‐allenylic pyridines.