Sc(OTf)3-catalyzed bicyclization of o-alkynylanilines with aldehydes: ring-fused 1,2-dihydroquinolines.

A Sc(OTf)3 -catalyzed cascade Prins-type cyclization reaction of o-alkynylanilines, bearing a hydroxy or amine functionality, with aldehydes affords 1,2-dihydroquinoline derivatives having an extra fused ring efficiently under mild reaction conditions. It is interesting to observe the reversed reactivity in the highly selective formation of 1,2-dihydroquinoline derivatives instead of the formation of the usually favored indole derivatives.