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.