Synthesis of Benzarsoles by Arsenic Cation-Mediated Formal [3 + 2]-Cycloaddition with Alkynes

A Tf2O-mediated formal [3 + 2]-cycloaddition of phenylarsine oxide and internal alkynes has been developed. An initially formed arsenic dication undergoes disproportionation to form key arsenic cation species, which are then coupled with alkynes, finally delivering the corresponding 2,3-disubstituted benzarsole derivatives with concomitant unique phenyl group migration. This strategy is also applicable to the three-component coupling of phenylarsine oxide, arylboronic acids, and alkynes. Moreover, ring transformations of the obtained benzarsoles are described.