Sc(OTf)3-catalyzed diastereoselective [4+2] cycloaddition reaction of 3-benzylideneindoline-2-thiones with alkylidene malonates

A Sc(OTf)3-catalyzed diastereoselective [4 + 2] cycloaddition reaction of 3-benzylideneindoline-2-thiones with 2-alkylidene malonates has been realized, leading to biologically important indole-annulated thiopyran derivatives in moderate to good yields. Moreover, a gram-scale reaction and chemical transformation of the cycloadduct into a sulfone were carried out to further extend the synthetic utility.