Acid-promoted formal [3 + 2] cyclization/N,O-ketalization of in situ generated ortho-alkynyl quinone methides: access to bridged 2,3-cyclopentanoindoline skeletons

Abstract

An acid-catalyzed formal [3 + 2] cyclization/N,O-ketalization of in situ formed ortho-alkynyl quinone methides (o-AQMs) and tryptophol derivatives was developed. With this method, a series of functionalized 2,3-cyclopentanoindoline derivatives were effectively synthesized in good yields with excellent diastereoselectivities under mild conditions. In this reaction, o-AQMs formally serve as synthetic equivalents of the 1,3-dipole, and the process involves a tandem 1,4-addition/dearomatization/1,2-shift/aromatization sequence of tryptophol.