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)
