In synthetic organic chemistry, aryl boronic acids and esters are of extreme importance due to their ability to form carbon-carbon bonds through metal-catalyzed cross-coupling reactions. These coupling reactions with aryl halides or aryl triflates have become one of the most widely applied methods for constructing unsymmetrical biaryl systems, which are widely used in pharmaceuticals and agrochemical industries, and are present in bioactive natural products. The Suzuki-Miyaura coupling reaction is the most popular method for synthesizing unsymmetrical biaryls due to its general applicability and efficiency.
The popularity of these coupling reactions has prompted researchers to explore efficient methods for the synthesis of boronic acids. Traditionally, arylboronic acids are produced via transmetallation of Grignard reagents or organolithium reagents with trialkylborates, followed by acid hydrolysis. Despite moderate to good yields of alkyboronic acid, this method produces a mixture of mono- and dialkylated products, demonstrating poor selectivity.
Several alternative methods for synthesizing boronic acids have required transition metals and various exotic ligands. These procedures involve the cross-coupling of expensive boron sources, such as tetra(alkoxo)diboron derivatives or dialkoxyborane derivatives, with aryl halides and aryl triflates. In addition, these methods also require an excess of the boron reagent and low reaction temperatures. The synthesis of boronic esters also uses expensive and toxic catalysts including iridium, rhodium, and palladium.
Researchers at UC Santa Cruz have developed a method for the synthesis of both aryl and alkyl boronic esters and acids which is inexpensive, efficient, environmentally friendly, and does not require heavy metal catalysts. Many aryl boronic esters and aryl boronic acids can be synthesized in greater than 90% isolated yield at ambient reaction conditions.
|United States Of America||Issued Patent||9,243,004||01/26/2016||2009-268|
Additional Patent Pending
Synthetic chemicals, bioactive, aryl, boronic, acids, esters, C-C bonds, metal, pharmaceuticals, agrochemical, natural products, Cat2