Miyaura borylation

Palladium-catalyzed reaction of aryl halides with diboron reagent to produce aryl-boronates. Also known as Hosomi-Miyaura borylation. 

The Miyaura borylation reaction enables the synthesis of boronates by cross-coupling of bis(pinacolato)diboron (B2pin2) with aryl halides and vinyl halides. 

Finally, as shown by Kabalka and Yao [131] bis(pinacolato)diboron can be applied in a sequential Pd-catalyzed Miyaura borylation and Suzuki coupling to a (bromomethylene)cyclobutane furnishing an efficient synthesis of the (dicyclobutylidene)-ethane derivative 184, whereas the presumed boronate intermediate 185 was only obtained in trace amounts (Scheme 72). 

Another solution is to employ trifluoroborate salts 2.215, which can be prepared from the boronic acid by treatment with potassium hydrogen fluoride (Scheme 2.74). They can also be prepared from alkyl bo-ranes in a similar way (Scheme 2.75). These stable salts can be efficiently employed in Suzuki coupling reactions (Scheme 2.T6)P One application is in the synthesis of the unusual amino acid, trityrosine 2J26 (Scheme 2.77). In this synthesis an aryl diiodide 2.222 was coupled with a trifluoroborate salt 2.224 that had been formed by Miyaura borylation of iodide 2.223 followed by KHF2 treatment. Global debenzylation of coupling product 2.225 gave the product 2.226. Another example of the use of a trifluoroborate salt can be found in Scheme 2.88. 

A variant of these reactions was optimized based on the Hosomi-Miyaura borylation of a,P-unsaturated carbonyl compounds with nucleophilic boryl copper, providing 2-alkoxycarbonyl (as well as 2-acyl- and 2-cyano) allylboronates such as 40 in high stereoselectivity (Equation 22) [60]. The resulting 2-alkoxycarbonyl reagents react with aldehydes to provide a-methylene-y-butyrolactones. 

Ramachandran PV, Pratihar D, Biswas D, Srivastava A, Venkat Ram Reddy R. Novel functionalized trisubstituted aUylboronates via Hosomi—Miyaura borylation of functionalized allyl acetates. Org Lett. 2004 6 481-485. 

Fig. 5.17 The Miyaura borylation reaction. (From http-JAMWW.organic-chemistry.org/namedreactions/...

Fig. 5.18 The catalytic cycle of the Miyaura borylation reaction. (From httpj/www.organic-chemistry. org/namedreactions/miyaur3.GIF).

Scheme 3.76 Allylic boronates via Hosomi-Miyaura borylation.

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