Arylboronic acids [Ar-B(OH)
2] are very useful precursors used in Pd-catalyzed Suzuki Couplings, where almost any organic halide can be coupled with an arylboronic acid, one example being that allyl bromide would give allylbenzenes.
General procedure for arylboronic acid synthesis1Magnesium turnings (30 mmol) were placed in a round-bottomed flask and then flame-dried under N
2. Aryl bromide (30 mmol) dissolved in THF (20 mL) was added with an addition funnel to the flask slowly. The reaction mixture was gently refluxed for 3 to 4 h. After cooling, the Grignard reagent was transferred to a solution of (CH
3O)
3B in THF (10 mL) at -78°C and stirred overnight while warming up to RT slowly. After acidification with 10% HCl (10 mL), the product was extracted into ether (3x100 mL) and dried (sodium sulfate). The solvent was then removed under reduced pressure, and the products was precipitated by hexane with further recrystallization from water.
p-Tolylboronic acid: white needles were obtained in 81% yield; mp 243-244°C (lit.
2 242-243°C).
p-Methoxyphenylboronic acid: White needles were obtained in 72% yield; mp 197-198°C (lit.
2 202-205°C).
Arylboronic Acid References:[1]: Tetrahedron 51(11), 3129 (1995)
[2]: J. Am. Chem. Soc. 53, 711 (1931)
Suzuki CouplingIn this reaction is a bromo compound R-Br coupled to a boronic acid R'-B(OH)2 with Pd-catalyst. In the first step the bromo compound is added oxidative at Pd(0) and the bomide is metathetically substituted by an hydroxy ion. After trans-metallation and secession of tetrahydroxyborate the Pd(II) with both organic moieties is obtained. The Pd is reductively eliminated and the residues coupled to R-R'.
Suzuki Coupling References:http://themerckindex.cambridgesoft.com/TheMerckIndex/NameReactions/ONR388.htm
http://www.chempensoftware.com/reactions/rxn566.htm
http://www.mdpi.net/ecsoc-5/e0029/e0029.htm
http://www.sigmaaldrich.com/img/assets/3460/al_arylboronic_acids.pdf