Synthesis of arylboronic acids and arylboronates
A general and convenient protocol for the electrophilic borylation of aryl Grignard reagents prepared from arylbromides by direct insertion of magnesium in the presence of LiCl or by Mg/Br exchange with iPrMgCl·LiCl enables the synthesis of various aryl boronic acids in a straightforward manner in excellent yields at 0°C.
T. Leermann, F. R. Leroux, F. Colobert, Org. Lett., 2011, 13, 4479-4481.
Aliphatic, aromatic, heteroaromatic, vinyl, or allylic Grignard reagents react 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.
Borylzincate can be generated in situ from dialkylzinc, diboron, and metal alkoxide. Model DFT calculations show that although the formation of borylzincate is kinetically favorable, it is thermodynamically unfavorable. A successive reaction sequence, that provides a compensating energy gain, therefore enables Zn-catalyzed borylation of aryl halides and borylzincation of benzynes and terminal alkyne from diborons without the need for any cocatalyst.
Y. Nagashima, R. Takita, K. Yoshida, K. Hirano, M. Uchiyama, J. Am. Chem. Soc., 2013, 135, 18730-18733.
A highly efficient palladium-catalyzed borylation allows the conversion of aryl and heteroaryl iodides, bromides, and several chlorides containing a variety of functional groups to the corresponding corresponding pinacol boronate esters with an inexpensive and atom-economical boron source, pinacol borane.
K. L. Billingsley, S. L. Buchwald, J. Org. Chem., 2008, 73, 5589-5591.
The combination of Pd(dba)2 and bis(2-di-tert-butylphosphinophenyl)ether is an efficient catalyst system for the crosscoupling of pinacolborane with aryl bromides. This system enables the synthesis of ortho-, meta-, and para-substituted electron-rich and -deficient arylboronates. A temperature of 120°C was required for the conversion of electron-rich aryl chlorides.
M. Murata, T. Sambommatsu, S. Watanabe, Y. Masuda, Synlett, 2006, 1867-1870.
The CuI-catalyzed coupling reaction of pinacolborane with aryl iodides under the action of sodium hydride in THF at room temperature provided the corresponding arylboronates in good yields. Aryl bromides gave poor conversion.
W. Zhu, D. Ma, Org. Lett., 2006, 8, 261-263.
The highly active mixed-ligand catalytic system NiCl2(dppp)/dppf combined with the reducing effect of zerovalent Zn enables a dramatic acceleration of the rate of the neopentylglycolborylation of aryl halides. A diversity of electron-rich and electron-deficient aryl iodides, bromides, and chlorides were efficiently neopentylglycolborylated in very good yields, typically in 1 h or less.
P. Leowanawat, A.-M. Resmerita, C. Moldoveanu, C. Liu, N. Zhang, D. A. Wilson, L. M. Hoang, B. M. Rosen, V. Persec, J. Org. Chem., 2010, 75, 7822-7828.
The mixed-ligand system NiCl2(dppp)/dppf is an effective catalyst for the neopentylglycolborylation of ortho-, meta-, and para-substituted electron-rich and electron-deficient aryl mesylates and tosylates. The addition of Zn powder as a reductant dramatically increases the reaction yield and reduces the reaction time, providing complete conversion in 1-3 h.
D. A. Wilson, C. J. Wilson, C. Moldoveanu, A.-M. Resmerita, P. Corcoran, L. M. Hoang, B. M. Rosen, V. Percec, J. Am. Chem. Soc., 2010, 132, 1800-1801.
The presence of bis[2-(N,N-dimethylamino)ethyl] ether allows a selective halide-magnesium exchange of iodo- and bromoaromatics bearing sensitive carboxylic ester and cyano groups with isopropylmagnesium chloride. A subsequent reaction with trimethylborate as electrophile afforded arylboronic acids in good to excellent yields.
X.-J. Wang, X. Sun, L. Zhang, Y. Xu, D. Krishnamurthy, C. H. Senanayake, Org. Lett., 2006, 8, 305-307.
Arylboronic acids and aryl trifluoroborates are synthesized in a one-pot sequence by Ir-catalyzed borylation of arenes. To prepare the arylboronic acids, the Ir-catalyzed borylation is followed by oxidative cleavage of the pinacol boronates with NaIO4. To prepare the aryltrifluoroborate, the Ir-catalyzed borylation is followed by displacement of pinacol by KHF2.
J. M. Murphy, C. C. Tzschucke, J. F. Hartwig, Org. Lett., 2007, 9, 757-760.
Ir complexes with bidentate silyl ligands that contain P- or N-donors are effective catalysts for ortho borylations of a broad range of substituted aromatics. The substrate scope is broad, and the modular ligand synthesis allows for flexible catalyst design.
B. Ghaffari, S. M. Preshlock, D. L. Plattner, R. J. Staples, P. E. Maligres, S. W. Krska, R. E. Maleczka, Jr., M. R. Smith, III, J. Am. Chem. Soc., 2014, 136, 14345-14348.
The palladium catalysed cross-coupling reaction of aryl iodides and bromides with pinacolborane in 1,3-dialkylimidazolium tetrafluoroborates and hexafluorophosphates offers simple product isolation by extraction and shorter reaction time as compared to conventional solvents.
A. Wolan, M. Zaidlewicz, Org. Biomol. Chem., 2003, 1, 3724-3276.
meta- and para-dibromoarenes can be converted to isopropoxide-protected bromo arylboronates. A subsequent metal-halogen exchange and reaction with an electrophile leads to functionalized arylboronates in a one-pot manner.
Q. Jiang, M. Ryan, P. Zhichkin, J. Org. Chem., 2007, 72, 6618-6620.
Diazotization of arylamines promoted by methanol with sodium nitrite and hydrochloric acid as diazotization agents followed by Sandmeyer borylation via a SN2Ar pathway provides a simple and green method to arylboronic acids and arylboronates.
C.-J. Zhao, D. Xue, Z.-H. Jia, C. Wang, J. Xiao, Synlett, 2014, 25, 1577-1584.
The reaction of aryl cyanides with diboron in the presence of a rhodium/Xantphos catalyst and DABCO affords arylboronic esters via carbon-cyano bond cleavage. The reaction allows the regioselective introduction of a boryl group in a late stage of synthesis.
M. Tobisu, H. Kinuta, Y. Kita, E. Rémond, N. Chatani, J. Am. Chem. Soc., 2012, 134, 115-118.
AuCl3-catalyzed halogenations of aryl borononates with N-halosuccinimides enables a convenient synthesis of aromatic boronates bearing halogen substituents in the aromatic ring.
D. Qiu, F. Mo, Z. Zheng, Y. Zhang, J. Wang, Org. Lett., 2010, 12, 5474-5477.