^tBuOLi-Promoted Hydroboration of Esters and Epoxides

Abstract

Commercially available and inexpensive lithium tert -butoxide ( t BuOLi) acts as a good precatalyst for the hydroboration of esters, lactones, and epoxides using pinacolborane as a borylation agent. Functional groups such as cyano-, nitro-, amino-, vinyl, and alkynyl are unaffected under the presented hydroboration process, representing high chemoselectivity. This transformation has also been effectively applied to the synthesis of key intermediates of Erlotinib and Cinacalcet. Preliminary investigations of the mechanism show that the hydroboration proceeds through the in situ formed BH 3 species.

Vanadium-catalysed regioselective hydroboration of epoxides for synthesis of secondary alcohols

“…10 However, the substrate scope and functional group tolerance for the current vanadium catalyst are not as good as those known catalysts. [8][9][10][11][12][13] Based on previous reports 16,17 and the current results, a plausible mechanism that may operate for the regioselective hydroboration of epoxides is proposed (Scheme 6). As evidenced previously, vanadium complex 1 would first react readily with HBpin to generate a vanadium hydride species (A) by releasing TMSCH 2 Bpin from the reaction.…”

“…10 The simple lithium salt, t BuOLi was found to behave as a catalyst for hydroboration of several terminal epoxides at 100 °C to afford secondary alcohols, while it is also effective for the hydroboration of esters. 11 The Ren group later reported a NaOH/BEt 3 system effective for the hydroboration of a broad range of epoxides with complete Markovnikov selectivity. 12 In a recent work by Nembenna and coworkers, an aluminum dihydride catalyst supported by a N , N ′-chelated conjugated bis-guanidinate ligand enabled the hydroboration of epoxides with high regioselectivity for primary alcohols at 70 °C.…”

“…Comparing to other catalysts enabling regioselective hydroboration of epoxides reported thus far, 5–13 the current vanadium catalyst which features the first early transition-metal catalyst for Markovnikov-selective epoxide hydroboration shows higher reactivity ( i.e. lower catalyst loading and milder conditions) than those containing main-group metals, except the dimeric NaHBEt 3 /tpy complex.…”

“…10 However, the substrate scope and functional group tolerance for the current vanadium catalyst are not as good as those known catalysts. 8–13…”

Syntheses, characterizations and catalytic properties of three zinc complexes and one lithium compound chelated by β-diketiminate ligands

“…Alkali metal compounds [56][57][58][59][60] have been deemed to be more profitable than other catalysts due to their low budget and low pollution. These characteristics render alkali metal compounds very promising for use as catalysts in the catalytic hydroboration of aldehydes and ketones.…”