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.