A cascade reaction that generates pyrrolo- and pyridoindoline motifs from isocyanide precursors under phase-transfer conditions is described. This transformation proceeds at room temperature in the presence of a quaternary ammonium catalyst and base to generate functionalized products containing an all-carbon quaternary stereocentre. Quantum chemical calculations demonstrated that intramolecular general acid catalysis plays a key accelerating role through stabilization of developing charge in the transition state, and that the reaction is best described as a 5-endo dig cyclization, rather than an anionic 6π electrocyclization. Investigations employing chiral phase-transfer catalysts have given promising selectivities to date.
Keywords: cascade reactions; density functional calculations; heterocycles; hydrogen bonds; isocyanides; phase-transfer catalysis.
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