Regioselective Synthesis of Benzotriazoles via 1,7-Palladium Migration

Significance

Reported is the regioselective synthesis of benzotriazoles 2 from 1,3-diphenyltriazines 1 via a 1,7-palladium migration-cyclization-dealkylation sequence. EDGs on the bromoarene were found to afford lower yields of products, which were, however, increased by elevating the reaction temperature to 150 ˚C. Conversely, EDGs on the other aryl ring gave the best yields. Substrates incorporating steric hindrance near the ­reaction site (R^² = 4,6-Me₂ and 4-Me-5-Cl) also required higher reaction temperatures to obtain useful yields of products. Alkyl groups other than Me on the triazine (Et, i-Pr, n-Bu, t-Bu, Bn) all underwent dealkylation to give the desired products in 43-76% yield (cf. 75% with Me). A plausible mechanism involving a 1,7-palladium migration (3 → 4) is proposed based on detailed deuteration and control experiments.