Biaryl esters, preparation using boronic

The direct preparation of arylboronic esters from aryl halides or triflates now allows a one-pot, two-step procedure for the synthesis of unsymmetrical biaryls. The synthesis of biaryls was readily carried out in the same flask when the first coupling of aryl halide with diboron was followed by the next reaction with another halide or triflate [240]. The protocol offered a direct and efficient method for the synthesis of the boronic ester in the solid-phase that hitherto met with little success using classical methodology (Scheme 44). The solid-phase boronate (106, 107) [243] was quantitatively obtained by treating a polymer-bound haloarene with the diboron. The subsequent coupling with haloarenes furnished various biaryls. The robot synthesis or the parallel synthesis on the surface of resin is the topic of further accounts of the research. 

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. 

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