Oxidation of Olefins with Benzeneseleninic Anhydride in the Presence of TMSOTf

A new
oxidizing system for olefins, consisting of benzeneseleninic
anhydride and trimethylsilyl triflate, was studied. The highly reactive
benzeneseleninyl cation is presumably formed under these conditions.
It has been shown that different products are formed with this species
depending on the specific structure of olefin. The 1,1-disubstituted
olefins afforded mostly α,β-unsaturated carbonyl compounds.
The sterically encumbered tri- or tetrasubstituted olefins yielded
1,2- or 1,4-dihydroxylated products, presumably via four-membered
cyclic intermediates.