Halosulphonylation of Unsaturated Boronic Esters: Access to New Electron-Deficient Alkenes and Dienes

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Abstract
Sulphonyl halides undergo free radical addition to vinyl- and 1,3-dienylboronic esters (2-vinyl-1,3,2-dioxaborolanes 1 and 2-(1,3-alkadienyl)-1,3,2-dioxaborolanes 5] giving adducts which, in appropriate cases, afford upon treatment with base new β-sulphonyl α,β-unsaturated boronic esters [2-(2-p-toluenesulphonylethenyl)-1,3,2-dioxaborolanes 3 and 2-(4-p-toluenesulphonyl-1,3-butadienyl)-1,3,2-dioxaborolanes 6, respectively]. By using bromomethanesulphonyl bromide, the parent 1,3-butadienyl-2-boronic ester 8 was synthesized via a vinylogous Ramberg-Bäcklund rearrangement of the corresponding β-bromosulphone 7.

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