Enantioselective synthesis of indolo[2,3-b]-dihydrothiopyranones via [3+3] cycloaddition of chiral α,β-unsaturated acylammonium salts

A nucleophile-catalyzed Michael addition/proton transfer/lactonization (NCMPL) organocascade process of chiral α,β-unsaturated acylammonium salts and indoline-2-thiones is described, which delivers the indolo[2,3-b]dihydrothiopyranone motifs in high yields (up to 97%) with good to excellent enantioselectivities (up to 98% ee).