[4++2]-Type polar cycloadditions of 2-benzothiopyrylium salt with alkenes

Treatment of 2-benzothiopyrylium salt with alkenes such as styrene, p-methylstyrene, p-methoxystyrene, α-methylstyrene, and trans-anethole afforded the corresponding [4++2]-type polar cycloaddition products, respectively. The structures of the cycloadducts were confirmed by X-ray crystal structure determination of the corresponding sulfone derivative.