Convenient synthesis of tryptophols and tryptophol homologues by hydroamination of alkynes

A novel method is presented for the one-pot synthesis of substituted 3-(2-hydroxyethyl)- and 3-(3-hydroxypropyl)indoles (tryptophols and homotryptophols) from aryl hydrazines and silyl-protected ω-(hydroxyoalkyl)alkynes. Various tryptophol derivatives were prepared directly in good yield with excellent regioselectivity via a domino reaction sequence consisting of a titanium-catalyzed hydroamination of the alkyne, [3+3]-rearrangement of the resulting aryl hydrazone, and subsequent deprotection of the hydroxy group.

The first general method for the synthesis of tryptophol derivatives from aryl hydrazines and alkynes is presented.