Phosphine-Catalyzed Enantioselective Dearomative [3+2]-Cycloaddition of 3-Nitroindoles and 2-Nitrobenzofurans.

Over the past years, the metal-catalyzed dearomative cycloaddition of 3-nitroindoles and 2-nitrobenzofurans have emerged as a powerful protocol to construct chiral fused heterocyclic rings. However, organocatalytic dearomative reaction of these two classes of heteroarenes has become a long-standing challenging task. Herein, we report the first example of phosphine-catalyzed asymmetric dearomative [3+2]-cycloadditio of 3-nitroindoles and 2-nitrobenzofurans, which provide a new, facile, and efficient protocol for the synthesis of chiral 2,3-fused cyclopentannulated indolines and dihydrobenzofurans by reacting with allenoates and MBH carbonates, respectively through a dearomative [3+2]-cycloaddition.