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In this reaction dichloromethyllithium converts the boronic ester into a boronate. A Lewis acid then induces a rearrangement of the alkyl group with displacement of the chlorine group. Finally an organometallic reagent such as a Grignard reagent displaces the second chlorine atom effectively leading to insertion of an RCH 2 group into the C-B bond.
MIDA boronate esters and organotrifluoroborates have both been utilised in "slow release" strategies, in which the reaction conditions are optimised to provide a slow release of boronic acid. This protocol has proved useful in the cross-coupling of some notoriously unstable boronic acids, such as the 2-pyridine boronic acid.
The boron atom of a boronic ester or acid is sp 2 hybridized possessing a vacant p orbital, enabling these groups to act as Lewis acids. The C–B bond of boronic acids and esters are slightly longer than typical C–C single bonds with a range of 1.55-1.59 Å.
Trimethyl borate is a popular borate ester used in organic synthesis. Borate esters form spontaneously when treated with diols such as sugars and the reaction with mannitol forms the basis of a titrimetric analytical method for boric acid. Metaborate esters show considerable Lewis acidity and can initiate epoxide polymerization reactions. [4]
β,γ-unsaturated, N-substituted amino acids are prepared through the condensation of organoboronic acids, boronates, or boronic esters with amines and glyoxylic acids. The highly polar protic solvents Hexafluoroisopropanol (HFIP) can shorten reaction time and improve yield. [17] PBM coupling to synthesize amino acid with HFIP solvent
The Miyaura borylation has shown to work for: Alkyl halides, [2] aryl halides, [1] [3] [4] aryl halides using tetrahydroxydiboron, [5] aryl halides using bis-boronic acid, [6] aryl triflates, [7] aryl mesylates, [8] vinyl halides, [9] vinyl halides of α,β-unsaturated carbonyl compounds, [10] and vinyl triflates.
Compounds of the type BR n (OR) 3-n are called borinic esters (n = 2), boronic esters (n = 1), and borates (n = 0). Boronic acids are key to the Suzuki reaction. Trimethyl borate, debatably not an organoboron compound, is an intermediate in sodium borohydride production.
The mechanism of organotrifluoroborate-based Suzuki-Miyaura coupling reactions has recently been investigated in detail. The organotrifluoroborate hydrolyses to the corresponding boronic acid in situ, so a boronic acid can be used in place of an organotrifluoroborate, as long as it is added slowly and carefully. [7] [8]