Boronic acid anhydrides esters, cyclic

The synthesis of lapatinib involves a Suzuki-Miyaura coupling of a (5-formylfuran-2-yl)boronic derivative and an aryl iodide and was studied in detail by several teams. " In a recent patent,researchers from Zentiva noticed that in their own attempts to use commercial boronic acid, the excess of this reagent required for optimal conversions and purity was dependent on the source (a common issue with boronic acids, which are often contaminated with anhydrides and borinic acid). Thus, they turned to cyclic boronic esters as a more reliable intermediate, allowing correct control of the amount of boron reagent. Transposition of a process originally developed for the coupling of (5-formylfuran-2-yl)boronic acid was successful. The authors compared... 

Like borinic adds, boronic acids are weak adds and are readily charao-terized as cyclic derivatives such as diethanolamine esters (3.26) pyridine adducts of their anhydrides (3.27) or as benzodiazaboroles (3.28). 

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