New Types of Reactivity of α,β‐Unsaturated N,N‐Dimethylhydrazones: Chemodivergent Diastereoselective Synthesis of Functionalized Tetrahydroquinolines and Hexahydropyrrolo[3,2‐b]indoles

The indium trichloride‐catalyzed reaction between aromatic imines and α,β‐unsaturated N,N‐dimethylhydrazones in acetonitrile afforded 1,2,3,4‐tetrahydroquinolines bearing a hydrazone function at C4 through a one‐pot diastereoselective domino process that involves the formation of two C? C bonds and the controlled generation of two stereocenters, one of which is quaternary. This reaction constitutes the first example of an α,β‐unsaturated dimethylhydrazone that behaves as a dienophile in a hetero Diels–Alder reaction. The related reaction between anilines, aromatic aldehydes, and methacrolein dimethylhydrazone in CHCl₃ with BF₃?Et₂O as catalyst afforded polysubstituted 1,2,3,3a,4,8b‐hexahydropyrrolo3,2‐b]indoles as major products through a fully diastereoselective ABB′C four‐component domino process that generates two cycles, three stereocenters, two C? C bonds, and two C? N bonds in a single operation.