Cycloadditions of Benzynes with the Azoxy [RN═N(O)R'] 1,3-Dipole Tautomer of 1-Hydroxybenzotriazole (HOBT).

1,3-Dipolar cycloadditions of azoxy species are rare. HOBT exists as a pair of tautomers, one of which contains an azoxy subunit. We show that heavily substituted, thermally generated benzynes react with HOBT by engaging the azoxy tautomer to give products having a benzotriazole with a benzyne-derived -hydroxyaryl group at N2. DFT calculations were used to probe aspects of the mechanism. HOBT analogs of the uronium family (HBTU, HCTU, TATU, and HATU) react in an analogous fashion. The parent 1,2-dehydrobenzene (-benzyne) generated by the action of (basic) CsF reacts with HOBT in an orthogonal manner to give, exclusively, an N1-arylated product.