Novel phenyl migration of 1-phenylbenzo[b]thiophenium triflates in the thermolysis

Thermolysis of 1-phenylbenzo[b]thiophenium triflates at 180°C causes phenyl migration to give 2-phenylbenzo[b]thiophenes in high yields. Interestingly, the thermolysis of 1-phenylbenzo[b]thiophenium triflates having a substituent at the 2 position affords the corresponding 3-phenylbenzo[b]thiophenes. On the basis of the thermolysis of 2-(4-methylphenyl)-1-phenylbenzo[b]thiophenium triflate, a consecutive [1,5] sigmatropic rearrangement is proposed for the phenyl migration.