TiCl4/t-BuNH2-promoted hydroamination/annulation of delta-keto-acetylenes: synthesis of novel pyrrolo[1,2-a]indol-2-carbaldehydes.

[reaction: see text] An original TiCl(4)/t-BuNH(2)-mediated hydroamination/annulation domino reaction of delta-keto-acetylenes is described. The synthesis of pyrrolo[1,2-a]indole-2-carbaldehydes, starting from 2-carbonyl-1-propargyl-1H-indoles runs under mild reaction conditions. A conceivable mechanism is also discussed. TiCl(4) has proved to be an effective multiactivity reagent: catalyst/Lewis acid/water scavenger. Some unpublished 2-carbonyl-1-propargyl-1H-indoles are prepared by means of Suzuki- and Negishi-type reactions.