Haloboration of Internal Alkynes with Boronium and Borenium Cations as a Route to Tetrasubstituted Alkenes

摘要

Vinyl boronates are extremely useful precursors, especially for the formation of new C-C bonds by cross-coupling and conjugate addition reactions. Although alkyne hydrobora-tion is a powerful synthetic route, it is not applicable to the synthesis of trisubstituted vinyl boronates. Thus, alternative regio-and stereospecific methods are needed, particularly for subsequent use in the formation of tetrasubstituted alkenes, as the production of these important biologically active compounds as single isomers by classical methods is challenging. One simple approach to trisubstituted vinyl boronates is the functionalization of internal alkynes by metal-catalyzed 1,2-carboboration and 1,1-carbobora-tion. The introduction of two selectively transformable moieties onto an internal alkyne should enable ready access to tetrasubstituted alkenes by successive cross-coupling reactions. Significant progress has been made in this area, particularly in the dimetalation of internal alkynes to provide two nucleophilic sites of distinct reactivity.