Arylboronic esterification

Arylboronic acids [63,72,80,85,194] have been most extensively studied as binding sites for derivatised monosaccharides. By using an amino group in the position ortho to the boronic add the rate constant for the esterification with a diol has been increased by a factor of 10 , as mentioned above [79], It has also been shown that the flexibility of the boronic add group is crucial. If the binding interaction is too rigid or too flexible, it is detrimental to the selectivity of the... 

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. 

Esterification of arylboronic acids Preparation of phenyl-1,4- diboronic acid bis-pinacol ester (266) 18/... 

Disubstituted-1,3,2-dioxaborinanes, 4.5, are structurally similar to 2,5-disubsti-tuted-1,3-dioxanes but without the complication of cis-/fra s-isomerism the creation of the dioxaborinane ring is achieved by esterification of a 2-substituted-propan-1,3-diol with an arylboronic acid [62, 63]. For compounds of this type with a 5-aryl substituent, 2-arylpropan-l,3-diols are required and are prepared by coupling the ethyl cyanoacetate anion and a 4-substitut-ed-phenyl bromide or iodide [62] and the 5-alkyl-substituted-1,3,2-dioxaborinanes [63] are obtained from 2-alkylpropan-1,3-diols (4.1). 

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