Subject boron halides

Two further methods of preparing organoboron compounds have been the subject of fairly recent detailed study, namely, reaction of boron halides with hydrocarbons and addition of boron hydrides to olefins. For instance, arylboron dihalides are formed when boron trihalides are heated with aromatic hydrocarbons, aluminum chloride, and aluminum powder,217 and phenyl-boron dibromide has been prepared analogously.218 Further, boron halides such as diboron tetrachloride and tetrafluoride add to olefins, yielding bis-(dichloroboryl) and bis(difluoroboryl) compounds 219... 

In studies concerned with optimization of the Suzuki cross-coupling of 2-pyridyl nucleophiles, lithium triisopropyl 2-pyridylborates are shown to be the most suitable boron coupling partners (eq 60). The borates are isolated and subjected to coupling with various aryl and hetaryl halides (X = Cl, Br) to give the corresponding azabiaryls. ... 

The Suzuki coupling was developed by Professor Akira Suzuki of Hokkaido University. The Suzuki coupling uses a boron compound (R-BYj) and an alkenyl, aryl, or alkynyl halide or triflate (RX) as the carbon sources, with a palladium salt as the catalyst. Bromides and iodides are the most commonly used halides chlorides are less reactive. Alkyl halides can sometimes be used but are subject to elimination. A base is also required. The boron compound can be a borane (R jB), a borate ester (R B(OR)2), or a boric acid (R B(OH)2), where R is alkyl, alkenyl, or aryl. The general reaction is shown in the following scheme, where X is halide or triflate and Y is alkyl, alkoxyl, or OH. A list of the types of components that can be used is given in Table 24.1. This reaction is one of the principal methods now used to prepare biaryls. 

Chemo- and regioselective ruthenium-catalyzed cyclotrimerization of alkynes was accomplished through a temporary boron tether. Crude aryl boronates were obtained in a one-pot procedure in which they were subjected to a Suzuki-Miyaura coupling with aryl halides (Scheme 9.50) [103]. 

The dioxaborole (97), formed from catecholborane and ethojqracetylene, undergoes a Pd-catalysed cross-coupling reaction with aryl or benzyl halides RX to give the vinyl ethers (98). Since these vinyl ethers can readily be hydrolysed to aldehydes (99), the overall sequence provides an efficient method for converting halides into aldehydes with two more carbon atoms. Also on the subject of boronic acid chemistry, a number of syntheses of the useful intermediates (100) have been published. ... 

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