Synthesis of alkylboronic acids and alkylboronates
A mild Pd-catalyzed process for the borylation of primary alkyl bromides using bis(pinacolato)diboron as a boron source tolerates a wide range of functional groups on the alkyl bromide substrate and offers complete selectivity in the presence of a secondary bromide. This approach has been extended to the use of alkyl iodides and alkyl tosylates, as well as borylation reactions employing bis(neopentyl glycolato)diboron as the boron source.
A. Joshi-Pangu, X. Ma, M. Diane, S. Iqbal, R. J. Kribs, R. Huang, C.-Y. Wang, M. R. Biscoe, J. Org. Chem., 2012, 77, 6629-6633.
A catalyst formed in situ from NiBr2 • diglyme and a pybox ligand accomplishes Miyaura-type borylations of unactivated tertiary, secondary, and primary alkyl halides with diboron reagents to furnish alkylboronates. The method exhibits good functional-group compatibility and is regiospecific.
A. S. Dudnik, G. C. Fu, J. Am. Chem. Soc., 2012, 134, 10693-10697.
orylation of primary and secondary alkyl chlorides, bromides, and iodides with diboron proceeded in the presence of copper(I)/Xantphos as catalyst and a stoichiometric amount of K(O-t-Bu) as base. Menthyl halides afforded the corresponding borylation product with excellent diastereoselectivity, whereas (R)-2-bromo-5-phenylpentane gave a racemic product.
H. Ito, K. Kubota, Org. Lett., 2012, 14, 890-893.
Aliphatic, aromatic, heteroaromatic, vinyl, or allylic Grignard reagents eact with pinacolborane at ambient temperature in tetrahydrofuran to afford the corresponding pinacolboronates. The initially formed dialkoxy alkylborohydride intermediate quickly eliminates hydridomagnesium bromide and affords the product boronic ester in very good yield. This reaction also can be carried out under Barbier conditions.
J. W. Clary, T. J. Rettenmaier, R. Snelling, W. Bryks, J. Banwell, W. T. Wipke, B. Singaram, J. Org. Chem., 2011, 76, 9602-9610.
Hydroboration of terminal and internal aliphatic alkenes with pinacolborane was carried out at room temperature in the presence of dppm and [Ir(cod)Cl]2 resulting in addition of the boron atom to the terminal carbon with a selectivity of more than 99%. A complex prepared from dppe and [Ir(cod)Cl]2 resulted in the best yields for vinylarenes.
Y. Yamamoto, R. Fujikawa, T. Umemoto, N. Miyaura, Tetrahedron, 2004, 60, 10695-10700.
A very active cobalt catalyst enables a facile anti-Markovnikov hydroboration of sterically hindered terminal alkenes. Notably, these hydroboration reactions proceed in neat substrates at 23°C. With internal olefins, the cobalt catalyst provides a convenient method for hydrofunctionalization of remote C-H bonds by placing the boron substituent exclusively at the terminal positions of an alkyl chain.
J. V. Obligacion, P. J. Chirik, J. Am. Chem. Soc., 2013, 135, 19107-19110.
Efficient and site selective boron-copper addition processes involving acyclic and cyclic disubstituted aryl olefins are promoted with a readily available N-heterocyclic carbene (NHC) complex. In situ protonation of the C-Cu bond in the presence of MeOH leads to efficient catalyst turnover, constituting a net Cu-catalyzed hydroboration process.
Y. Lee, A. H. Hoveyda, J. Am. Chem. Soc., 2008, 131, 3160-3161.
A simple protocol for the borylation of alkenes with use of impregnated copper on magnetite showed a very broad scope. All type of olefins could be used with similar results. The catalyst can be magnetically removed and reused several times, showing similar activity.
R. Cano, D. J. Ramón, M. Yus, J. Org. Chem., 2010, 75, 3458-3460.
A convenient method for the synthesis of 1,1-diboronates from the corresponding N-tosylhydrazones is also applicable to 1-silyl-1-boron compounds. Derivatization and consecutive Pd-catalyzed cross-coupling reactions with 1,1-boronates were also explored, demonstrating the synthetic potential of 1,1-diboronates.
H. Li, X. Shangguan, Z. Zhang, S. Huang, Y. Zhang, J. Wang, Org. Lett., 2014, 16, 448-451.
(E)- and (Z)-silyl and aryl-subsituted homoallylic methanesulfonates were converted to the corresponding cis- and trans-1-silyl-2-borylcyclobutanes as well as 1-phenyl-2-borylcyclobutanes in the presence of a CuCl/dppp catalyst, bis(pinacolato)diboron, and K(O-t-Bu)in THF. Stereospecific derivatizations of the cis- and trans-borylcyclobutanes were carried out to demonstrate the utility of the borylcyclobutanes.
H. Ito, T. Toyoda, M. Sawamura, J. Am. Chem. Soc., 2010, 132, 5990-5992.
Using bis(pinacolato)diboron, catalytic amounts of CuII, and various amine bases in water under atmospheric conditions at rt, acyclic and cyclic α,β-unsaturated ketones and esters are β-borylated in good yield. Mechanistic investigations suggest that the role of the amine is not only to coordinate to CuII but also to activate a nucleophilic water molecule to form a reactive sp2-sp3 diboron complex.
S. B. Thorpe, J. A. Calderone, W. L. Santos, Org. Lett., 2012, 14, 1918-1921.
A simple protocol for the borylation of alkenes with use of impregnated copper on magnetite showed a very broad scope. All type of olefins could be used with similar results. The catalyst can be magnetically removed and reused several times, showing similar activity
R. Cano, D. J. Ramón, M. Yus, J. Org. Chem., 2010, 75, 3458-3460.
A copper(I)-chiral secondary diamine complex catalyzes an enantioselective conjugate boration of β,β-disubstituted enones in high yields and up to 99% ee. The resulting chiral tertiary organoboronates can be converted to enantiomerically enriched β-hydroxy ketones without any racemization.
I-H. Chen, M. Kanai, M. Shibasaki, Org. Lett., 2010, 12, 4098-4101.
A N-heterocyclic carbene (NHC) copper(I) complex generated in situ by the reaction of Cu2O and a planar and centrally chiral bicyclic 1,2,4-triazolium salt was an efficient catalyst for the asymmetric β-boration of acyclic enones, producing β-boryl ketones in high yields and enantioselectivities.
L. Zhao, Y. Ma, F. He, W. Duan, J. Chen, C. Song, J. Org. Chem., 2013, 78, 1677-1681.
A new planar and central chiral bicyclic triazolium ligand enables a highly efficient copper-catalyzed asymmetric conjugate boration. This protocol gave various chiral secondary alkylboronates in very good ee. A preliminary mechanistic study supports the bifunctional nature of the catalyst.
L. Zaho, Y. Ma, W. Duang, F. He, J. Chen, S. Soung, Org. Lett., 2012, 14, 5780-5783.
A catalytic enantioselective conjugate boration of β-substituted cyclic enones in the presence of a QuinoxP*-CuOtBu complex produced enantiomerically enriched tertiary organoboronates. The substrate scope was broad, and high enantioselectivity was produced using both β-aromatic and aliphatic (linear and branched)-substituted cyclic enones with five- to seven-membered ring sizes.
I-H. Chen, L. Yin, W. Itano, M. Kanai, M. Shibasaki, J. Am. Chem. Soc., 2009, 131, 11284-11285.
(η6-mes)IrBpin3 or [Ir(COD)OMe]2 catalyzes the borylation of cyclopropanes in the presence of the phenanthroline derivative 2,9-Me2phenanthroline as ligand. The borylation occurs selectively at the methylene C-H bonds of the cyclopropane ring in high diasteroselectivities. The cyclopropylboronate esters can be converted to trifluoroborate salts, boronic acids, cyclopropylarenes, cyclopropylamines, and cyclopropanols.
C. W. Liskey, J. F. Hartwig, J. Am. Chem. Soc., 2013, 135, 3375-3378.
Rhodium-catalyzed asymmetric hydroboration of 3,3-disubstituted cyclopropenes gave 2,2-disubstituted cyclopropyl boronates with high degrees of diastereo- and enantioselectivity. Suzuki cross-coupling reaction of selected cyclopropylboronic derivatives produced corresponding optically active aryl- and vinylcyclopropanes in good yields.
M. Rubina, M. Rubin, V. Gevorgyan, J. Am. Chem. Soc., 2003, 125, 7198-7199.
A dramatic rate acceleration in the copper-catalyzed addition of bis(pinacolato)diboron to α,β-unsaturated carbonyl compounds was realized by adding alcohol additives. Various α,β-unsaturated carbonyl compounds were reacted to the corresponding β-boryl carbonyl compounds in high yields.
R. Varala, S. Nuvula, S. R. Adapa, J. Org. Chem., 2006, 71, 8283-8286.
A nickel catalyst system enables the β-boration of di-, tri-, and tetrasubstituted α,β-unsaturated esters and amides with bis(pinacolato)diboron in good yields.
K. Hirano, H. Yorimitsu, K. Oshima, Org. Lett., 2007, 9, 5031-5033.
Aryl cyclopropyl ketones undergo nickel-catalyzed borylative ring opening with bis(pinacolato)diboron to yield 4-oxoalkylboronates in good yield.
Y. Sumida, H. Yorimitsu, K. Oshima, J. Org. Chem., 2009, 74, 3196-3198.
Diboration of ketones with (ICy)CuOt-Bu as catalyst provides access to various tertiary α-hydroxyboronate esters. The catalyst was generated in situ with (ICy)CuCl and NaOt-Bu to afford a more efficient catalyst than the preformed (ICy)CuOt-Bu. Treatment of the resulting products with silica gel affords the corresponding α-hydroxyboronate esters.
M. L. McIntosh, C. M. Moore, T. B. Clark, Org. Lett., 2010, 12, 1996-1999.
A Cu-catalyzed regioselective and stereospecific aminoboration of styrenes with bis(pinacolato)diboron and O-benzoyl-N,N-dialkylhydroxylamines delivers β-aminoalkylboranes in good yields. The Cu catalysis enables introduction of both amine and boron moieties to C-C double bonds simultaneously in a syn fashion. Moreover, the use of a chiral biphosphine ligand, (S,S)-Me-Duphos, provides optically active β-aminoalkylboranes.
N. Matsuda, K. Hirano, T. Satoh, M. Miura, J. Am. Chem. Soc., 2013, 135, 4934-4937.
The Suzuki-Miyaura cross-coupling reaction between a diborylmethane derivative and allyl halides or benzyl halides proceeded efficiently in the presence of an appropriate Pd-catalyst at room temperature. The present approach provides functionalized homoallylboronates and alkylboronates with excellent regio- and chemoselectivities.
K. Endo, T. Ohkubo, T. Ishioka, T. Shibata, J. Org. Chem., 2012, 77, 4826-4831.