Diarylboronic acids

Thus formed, organometallics are trapped with tiialkyl borates to produce whether the desired arylboronic [149-151,153] or diarylboronic esters [152], depending on the reaction conditions discussed above. The diarylboronic acids have also been successfully used in the Pd(PPh3)4-catalysed SM reactions with aryl triflates, under the standard conditions [152]. Beside trialkyl borates, A,A-dimethylaminoboron bromide has been trapped with organolithiums to give an unstable bis-aminoboronate 349, which, upon esterification with pinacol, gave the 1,4-phenylene-bis-pinacolato boronate (266) in 21% overall yield [154], Scheme 50. 

A new promising method for the synthesis of mixed biaryls consists in the reaction of the ethanolamine esters of diarylboronic acids with NBS in dichloro-methane/aqueous buffer at pH 9. In this way, 2- and 3-phenylthiophen, 2,2 -bi-thienyl, and 2-(2-thienyl)furan were obtained. The nitration of 2,3 -bithienyl has been studied. 2-Nitro-2 -amino-3,3 -bithienyl and 3-nitro-3 -amino-2,2 -bithienyl have been found to be stable. Carbonyl derivatives of 2-aryl-thiophens have been prepared, and reactivity constants for 2-aryl-thiophens determined. Some 2,5-bis(4 -n-alkyldiphenyl-4"-yl)thiophens, which are liquid crystals, have been prepared from the corresponding 1,4-diketones and P4S10. Various naphthyl-thiophens have been synthesized in order to study their anti-inflammatory and antibacterial properties. ... 

The electron-donor N -oxide oxygen atom of a nitrone makes it suitable for com-plexation and protonation. Such properties of nitrones have been widely used to influence their reactivity, using Lewis acids and protonation in nucleophilic addition reactions (see Section 2.6.6). In this chapter, the chemistry of nitrones with various metal ions [Zn (II), Cu(II), Mn (II), Ni (II), Fe (II), Fe (III), Ru (II), Os (II), Rh (I), UO2 2 ] (375, 382, 442-445), and diarylboron chelates is described (234—237, 446). Accurate descriptions of the structures of all complexes have been established by X-ray analysis. 

The Suzuki polymerization is the AA-BB type, and the monomers are usually diarylbromide compounds and diarylboronate esters. It is possible to use diboronic acids as monomers, but the diboronate esters are generally used because they are more easily purified than diboronic acids. 

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