Benzyne Cascade Reactions via Benzoxetenonium Ions and Their Rearrangements to o-Quinone Methides

A new thermal isomerization of polyynes is described. Benzyne intermediates substituted by a C(RR')OR '' substituent adjacent to one of the benzyne sp-hybridized carbons give rise to products in which the OR' moiety has migrated to the proximal benzyne carbon. This process likely proceeds via sequential formation of multiple reactive intermediates: an initial thermally generated benzyne, a strained benzoxetenonium ion, and an o-quinone methide. As some examples demonstrate, the overall transformation can be quite efficient. The mechanism of this novel reaction is further supported by experiments and DFT calculations.