Synthesis of Indolyl-Tethered Spiro[cyclobutane-1,1′-indenes] through Cascade Reactions of 1-(Pyridin-2-yl)-1H-indoles with Alkynyl Cyclobutanols

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Presented herein is an efficient and unprecedented synthesis of indolyl-tethered spiro[cyclobutane-1,1′-indenes] through the cascade reaction of 1-(pyridin-2-yl)-1 H -indoles with alkynyl cyclobutanols. Mechanistic experiments implicate a sequential process in which 1-(pyridin-2-yl)-1 H -indole first undergoes an alkenylation with alkynyl cyclobutanol followed by an intramolecular Friedel–Crafts reaction to give the title products. The utility of this novel protocol was reflected by the ample substrate scope, high chemo- and regioselectivity, removable directing group, and scalable preparation. In addition, the product thus obtained can be further derivatized quite efficiently.