alkenylboranes

Alkenylboranes are organoboron compounds in which boron is directly bonded to a vinyl (alkenyl) carbon, forming a B–C(sp2) bond adjacent to a carbon–carbon double bond. The simplest member, vinylborane (H2B–CH=CH2), can be synthetically generalized to substituted forms such as R2B–CH=CH–R' carries. These species are valued as versatile synthetic intermediates in organic chemistry.

Preparation of alkenylboranes commonly involves the hydroboration of alkynes with borane reagents (for example BH3·THF or catecholborane). Hydroboration of terminal alkynes typically furnishes vinylboranes with defined stereochemistry (E or Z depending on substrate and conditions). Internal alkynes can also be converted to vinylboranes, and, for practical use, the reactive vinylborane unit is often captured as a more stable vinyl boronate ester (for instance, the pinacol boronate) by transesterification or direct formation during workup.

Reactivity and applications center on the transformations typical of organoboron reagents. Vinylboranes can be converted to vinyl boronates that participate in Suzuki–Miyaura cross-couplings, enabling construction of substituted alkenes by coupling the vinyl fragment with aryl or alkyl halides. They also serve as precursors to various functionalized alkenes through oxidation, transmetallation, or further boron–carbon bond transformations. Their utility lies in enabling alkenyl installations and enabling sequential carbon–carbon bond-forming sequences in a modular fashion.

See also: boranes, vinyl boronates, Suzuki coupling, hydroboration.