The three-component free-radical carbo-alkenylation of electron-rich olefins has been studied, varying the substitution pattern in the alkene, in the radical precursor and in the final acceptor. New vinylsulfones were also prepared and their reactivity investigated. The scope and limitations of the process was established, and the reaction mechanism clarified using selected dienes as radical clocks. It was thus recognised that the reversible addition onto the olefin of the released sulfonyl group is an important event, which should not be overlooked when using such multicomponent carbo-alkenylation reactions.
This review provides an overview of the recent progress made in the area of free-radical additions across the π-system of olefins, with a focus on the role of sulfonyl derivatives as one of the reaction partners in multicomponent processes. The mechanism and utility in organic synthesis of carbo-alkenylation, alkynylation, oximation and azidation of olefins are thus discussed and illustrated with some applications in total synthesis of natural products.
New bifunctional reagents for free-radical carbo-oximation of olefins have been developed. In this process, a single reagent can act both as a trap for nucleophilic radicals as well as a source of electrophilic radical via an α-scission of an alkylsulfonyl radical. This strategy involving the addition of a C-centered electrophilic radical and an oxime across the double bond of an electron-rich alkene is initiated with a t-BuO radical following an unusual mechanism, supported by both experiments and density functional theory calculations.
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