Selectivity between an Alder–ene reaction and a [2 + 2] cycloaddition in the intramolecular reactions of allene-tethered arynes

Abstract

Substituent-dependent reactivity and selectivity in the intramolecular reactions of arynes tethered with an allene are described. With a 1,3-disubstituted allene moiety, an Alder–ene reaction of an allenic C–H bond is preferred over a [2 + 2] cycloaddition, whereas a [2 + 2] cycloaddition of the terminal π-bond of the allene is preferred with a 1,1-disubstituted allene. With a 1,1,3-trisubstituted allene-tethered aryne, an Alder–ene reaction with an allylic C–H bond is preferred over a [2 + 2] cycloaddition.