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6.1.7.1 Method 1: Direct Borylation of Alkanes and Arenes

DOI: 10.1055/sos-SD-006-00221

Miyaura, N.Science of Synthesis, (20056257.

The reaction of aromatic hydrocarbons with boron trichloride or boron tribromide in the presence of a Lewis acid catalyst generated in situ from aluminum powder, iodine, and iodomethane yields aryl(dihalo)boranes in high yields, which are easily hydrolyzed to boronic acids with water. The syntheses of phenylboronic acid (1) and (4-phenoxyphenyl)boronic acid (2) from benzene and diphenyl ether, respectively, are such examples (Scheme 1).[‌7‌,‌8‌] The procedure is economical for large-scale preparations, but the protocol can only be used for a limited number of aromatic compounds; this is because the reaction generally results in a mixture of ortho-, meta-, and para-isomers for substituted arenes. For example, the borylation of toluene at 30°C yields para- and meta-isomers in a ratio of about 4.6:1. The distribution of isomers is comparable to that of the FriedelCrafts reaction with aluminum trichloride.

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