Boronic acid



  A boronic acid is an tetrahedral boronate complexes with pKa ~7. They are occasionally used in the area of molecular recognition to bind to saccharides for fluorescent detection or selective transport of saccharides across membranes.

Boronic acids are used extensively in Suzuki coupling. A key concept in its chemistry is transmetallation of its organic residue to a transition metal.

The compound proteasomes are blocked that would otherwise degrade proteins

Boronic acids

Many air-stable boronic acids are commercially available. They are characterised by high melting points.

Boronic acidRMelting point °C
Phenylboronic acidPhenyl121.9398-80-6216-219
2-Thienylboronic acidThiophene127.966165-68-0138 -140
Methylboronic acid Methyl59.8613061-96-659.86
cis-Propenylboronic acidpropene85.907547-96-865-70
trans-Propenylboronic acidpropene85.907547-97-9123-127
Representative boronic acids [1]

Borinic acids and esters

Borinic acids and borinic esters have the general structure R2BOR.

compoundgeneral formulageneral structure
boronic acidRB(OH)2
boronic ester
(boronate ester)		RB(OR)2
borinic acidR2BOH
borinic ester
(borinate ester)		R2BOR

Boronic esters

When hydrogen is replaced by any organic residue the resulting compound is called a boronic ester or boronate ester. The compounds can be obtained from diols. Phenylboronic acid can be selfcondensed to the cyclic trimer called triphenyl anhydride or triphenylboroxin [3]

Boronic esterdiolBoiling point °C
Allylboronic acid pinacol ester pinacol168.0472824-04-5 50-53°C 5 mm Hg
Phenyl boronic acid glycol estertrimethylene glycol161.994406-77-3106°C 2 mm Hg
Diisopropoxymethylboraneisopropanol144.02 86595-27-9105 -107°C
Representative boronic esters [4]

Compounds with 6-membered cyclic structures containing the C-O-B-O-C linkage are called dioxaborolanes and those with 5-membered rings dioxaborinanes.

Boronate or borate salts

Boronate salts or borate salts (not encouraged) are ate complexes and have the general structure R4B-M+ for example potassium tetraphenylborate.

Boronic acids in organic chemistry

Suzuki coupling reaction

Boronic acids are used in Suzuki reaction. In this reaction the boron atom exchanges its aryl group with an alkoxy group from palladium.

Chan-Lam coupling

In the Chan-Lam coupling the alkyl, alkenyl or aryl boronic acid reacts with a N-H or O-H containing compound with Cu(II) such as 2-pyridone with trans-1-hexenylboronic acid:

The catalytic systems oxygen also regenerates the Cu(II) catalyst.

Conjugate addition

The boronic acid organic residue is a nucleophile in dibenzylidene acetone in a such a conjugate addition [7]:

The tricyclohexylphosphine.

Another conjugate addition is that of cyclooctadiene rhodium chloride dimer [8]:

Oxidation

Boronic esters are oxidized to the corresponding alcohols with base and carbenoid)

Homologization

  • In boronic ester shifts from boron in a boronate to carbon [9]:
Boronic ester homologization mechanismHomologization application

In this reaction Petasis reaction.

Electrophilic allyl shifts

Allyl boronic esters engage in electrophilic allyl shifts very much like silicon pendant in the Sakurai reaction. In one study a diallylation reagent combines both [10][11]:

Hydrolysis

pyridine [12].

See also

References

  1. ^ www.sigmaaldrich.com
  2. ^ (1973) "Phenols: 6-Methoxy-2-Naphthol". Org. Synth.; Coll. Vol. 5: 918. 
  3. ^ Robert M. Washburn, Ernest Levens, Charles F. Albright, and Franklin A. Billig (1963). "Benzeneboronic Anhydride". Org. Synth.; Coll. Vol. 4: 68. 
  4. ^ www.sigmaaldrich.com
  5. ^ Copper promoted C-N and C-O bond cross-coupling with phenyl and pyridylboronatesTetrahedron Letters, Volume 44, Issue 19, 5 May 2003, Pages 3863-3865 Dominic M. T. Chan, Kevin L. Monaco, Renhua Li, Damien Bonne, Charles G. Clark and Patrick Y. S. Lam doi:doi:10.1016/S0040-4039(03)00739-1
  6. ^ Copper-promoted/catalyzed C-N and C-O bond cross-coupling with vinylboronic acid and its utilities Tetrahedron Letters, Volume 44, Issue 26, 23 June 2003, Pages 4927-4931 Patrick Y. S. Lam, Guillaume Vincent, Damien Bonne and Charles G. Clark doi:doi:10.1016/S0040-4039(03)01037-2
  7. ^ Catalytic Conjugate Addition of Allyl Groups to Styryl-Activated Enones Joshua D. Sieber, Shubin Liu, and James P. Morken J. Am. Chem. Soc.; 2007; 129(8) pp 2214 - 2215; (Communication) doi:10.1021/ja067878w
  8. ^ Benzylic Substitution of Gramines with Boronic Acids and Rhodium or Iridium Catalysts Gabriela de la Herrán, Amaya Segura, and Aurelio G. Csák Org. Lett.; 2007; 9(6) pp 961 - 964; (Letter) doi:10.1021/ol063042m
  9. ^ 99% Chirally selective synthesis via pinanediol boronic esters: insect pheromones, diols, and an amino alcohol Donald S. Matteson, Kizhakethil Mathew Sadhu, and Mark L. Peterson J. Am. Chem. Soc.; 1986; 108(4); pp 810 - 819; doi:10.1021/ja00264a039
  10. ^ Simple, Stable, and Versatile Double-Allylation Reagents for the Stereoselective Preparation of Skeletally Diverse Compounds Feng Peng and Dennis G. Hall J. Am. Chem. Soc.; 2007; 129(11) pp 3070 - 3071; (Communication) doi:10.1021/ja068985t
  11. ^ In this sequence the boronic ester allyl shift is catalyzed by enantiomeric excess
  12. ^ New asymmetric syntheses with boronic esters and fluoroboranes Donald S. Matteson Pure Appl. Chem., Vol. 75, No. 9, pp. 1249–1253, 2003 Link.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Boronic_acid". A list of authors is available in Wikipedia.