Borane Mediated Conjunctive Coupling of Vinylboronates: Merging Boronate Complex with Hypervalent Iodine Chemistry

A three-component conjunctive coupling reaction of vinylboronic esters has been developed via 1,2-boronate rearrangement involving sulphur-centred nucleophiles. The 3-iodane compound Togni-II has been used as the electrophilic source of CF3 group to construct highly functionalized tertiary alkyl boronic esters. A broad array of substrates containing various functional groups has been well-accommodated with good to excellent isolated yield retaining the valuable boronic ester moiety in the products which can be subjected to further functionalization reactions. The mechanistic studies suggested an ionic pathway and crucial role of the boron Lewis acid BEt3 to activate the Togni-II reagent. Theoretical studies depicted the interaction between the sp3-boronate 1 complex and Togni-II-BEt3 adduct that precedes the 1,2-shift of the thiol-moiety followed by the formation of the coupling product.