Organocatalyzed Dearomative Cycloaddition of 2-Nitrobenzofurans and Isatin-Derived Morita-Baylis-Hillman Carbonates: Highly Stereoselective Construction of Cyclopenta[b]benzofuran Scaffolds

The first organocatalyzed asymmetric dearomative cycloaddition between 2-nitrobenzofurans and isatin-derived Morita-Baylis-Hillman carbonates has been developed. Using a modified cinchona alkaloid as the catalyst, a series of structurally diverse cyclopenta[b]benzofuran derivatives with three contiguous stereocenters, including a spiro-quaternary chiral center, could be smoothly obtained in excellent results (all cases >20:1 dr, up to 99% yield and 98% ee). The utility of this method was showcased by the versatile transformations of the product.