Microwave-assisted manganese(III) acetate based oxidative cyclizations of alkenes with β-ketosulfones

The microwave-assisted synthesis of 5-(4-nitrophenyl)-2-phenyl-4-(phenylsulfonyl)-2,3-dihydrofuran (5a) was performed via manganese(III) acetate based oxidative cyclization of 1-(4-nitrophenyl)-2-(phenylsulfonyl)ethanone (3a) with vinylbenzene (4a). This new protocol was applied to four sulfone derivatives (3a–d), using vinylbenzene (4a) and diphenylethene (4b), affording a series of 2,3-dihydrofurans (5a–d, 6a–d) in moderate to good yields (26–55%). Similar methodology, applied on allylbenzene (4c), surprisingly, led to dehydronaphthalene derivatives (7a–d) in moderate yields. The unexpected mechanism and the role of allylbenzene (4c) are herein discussed.