Transition-metal-promoted reactions of boron hydrides. 5. Palladium-catalyzed pentaborane(9)-olefin coupling reactions: a new, mild synthetic route to alkenylpentaboranes

Recent Advances in Organic Synthesis Using Transition Metal-Catalyzed Hydroborations

“…Although this chemistry was initially observed in reactions of pentaborane (9) [171,172] or borazine [173] and ethylene using PdBr 2 as the catalyst precursor, later work with HBcat and HBpin provided an avenue for generating synthetically useful alkenylboronate esters. Although this chemistry was initially observed in reactions of pentaborane (9) [171,172] or borazine [173] and ethylene using PdBr 2 as the catalyst precursor, later work with HBcat and HBpin provided an avenue for generating synthetically useful alkenylboronate esters.…”

Exploring the mechanism of the hydroboration of alkenes by amine–boranes catalysed by [Rh(xantphos)]+

“…Hydroboration, the addition of a B-H bond across an unsaturated C-C bond, is a versatile methodology that affords organoboranes, from which subsequent functionalisation leads to products of use in organic synthesis. [1][2][3][4] Non-metal catalysed hydroboration generally yields the anti-Markovnikov product, whereas transition metal catalysts enable control over the regioselectivity of hydroboration. Such selectivity (i.e.…”

Selective CH Borylation of Alkenes by Palladium Pincer Complex Catalyzed Oxidative Functionalization

“…The majority of the known CH borylation processes employ iridium,2a–f, 3 rhodium,2g–m or ruthenium2n–o catalysts. Interestingly, palladium catalysis, which is widely used in both CH functionalization4 and borylation reactions,5 has been employed relatively rarely 2p–s. In particular, only a limited number of studies2r–s have been performed on the palladium‐catalyzed borylation of alkenes using CH functionalization.…”

“…Interestingly, palladium catalysis, which is widely used in both CH functionalization4 and borylation reactions,5 has been employed relatively rarely 2p–s. In particular, only a limited number of studies2r–s have been performed on the palladium‐catalyzed borylation of alkenes using CH functionalization. One possible reason for this is that palladium is not efficient in cleaving vinylic/allylic CH bonds under the typical reducing conditions of borylation processes, using diboronates or borohydrides as boronate sources.…”

“…Probably the most important conceptually new feature of this CH borylation reaction is the possible formation of Pd IV intermediates, such as 12 , which presumably transmetalates with B 2 pin 2 more readily than the Pd II species, the most oxidized species in typical palladium‐catalyzed borylation reactions 5. To the best of our knowledge, there have been only two papers, published by Sneddon and co‐workers,2r–s on the palladium‐catalyzed CH borylation of alkenes. However, in these studies, borane clusters (pentaborane) were used as the boronate source and the catalytic reaction afforded an isomeric mixture of alkyl/vinyl pentaborane derivatives.…”