Enantioselective Vinylogous Michael-Michael Cascade Reactions of 3-Alkylidene Oxindoles and Nitroolefin Enoates.

A novel bifunctional squaramide catalyzed vinylogous Michael-Michael cascade reaction of 3-alkylidene oxindoles with nitroolefin enoates was developed. This convenient, one-pot cascade reaction serves as a powerful tool for the enantioselective construction of potential bioactive chiral chromans, which have three continuous tertiary stereocenters, in moderate to good yields (up to 85%) with excellent stereoselectivities (up to >19:1 dr and >99% ee).