BF3-Promoted Divergent Reactions between Tryptophols and Propargylic Alcohols.

Trifluoroboron-promoted cascade reactions between tryptophols and propagylic alcohols furnished three types of skeletons, including carbazoles, cyclopenta[b]furo[2,3-b]indoles, and allenyl furo[2,3-b]indoles, with excellent selectivity based on the substrate structure. Tryptophols without a substituent on the 2-position of the indole ring reacted with 1,1,3-triphenylprop-2-yn-1-ol and 9-(phenylethynyl)-9H-fluoren-9-ol to give carbazoles and cyclopenta[b]furo[2,3-b]indoles, respectively, while the reaction of 2-substituted tryptophols afforded allenylfuro[2,3-b]indoles.