Synthesis of vinylboronic acids and vinylboronates
Carboxylic acids are able to catalyze the direct hydroboration of various terminal and internal alkynes with pinacolborane without using any metal catalysts. This hydroboration exhibits a broad functional groups compatibility and gives the corresponding alkenyl diboronates and monoboronates in very good yields with exclusive regio- and stereoselectivities.
H. E. Ho, M. Asao, Y. Yamamoto, T. Jin, Org. Lett., 2014, 16, 4670-4673.
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.
Methylpentanediolborane can be prepared easily by reaction of hexyleneglycol with borane dimethylsulfide or B2H6 generated from NaBH4 and I2. MPBH hydroborates stereo- and regioselectively highly functionalized alkynes. MPBH compares favorably with pinacolborane in terms of reactivity. The obtained vinylboronic esters are air- and chromatography-stable.
N. PraveenGanesh, S. d'Hondt, P. Y. Chavant, J. Org. Chem., 2007, 72, 4510-4514.
A ruthenium hydride pincer complex catalyzes the anti-Markovnikov addition of pinacolborane to terminal alkynes yielding Z-vinylboronates at mild conditions. The catalytic cycle involves rearrangement of coordinated alkyne to Z-vinylidene as a key step for the apparent trans-hydroboration.
C. Gunanathan, M. Hölscher, F. Pan, W. Leitner, J. Am. Chem. Soc., 2012, 134, 14349-14352.
Ferric chloride catalyzes an efficient monoborylation of alkynes using bis(pinacolato)diboron to provide E-vinyl boronates with high regio- and stereoselectivity in good to excellent yields. Using iron nanoparticles, a high catalytic activity was observed and the catalyst could be recovered simply by using an external magnetic field. The magnetic nanoparticles were recycled six times without any significant loss of catalytic activity.
V. S. Rawat, B. Sreedhar, Synlett, 2014, 25, 1132-1136.
A silver(I)-N-heterocyclic carbene complex is a potent catalyst for formal hydroboration of alkynes, providing a variety of borylalkenes with high regio- and stereoselectivity. Under silver catalysis, allenes also undergo regioselective hydroboration to give borylalkenes.
H. Yoshida, I. Kageyuki, K. Takaki, Org. Lett., 2014, 16, 3512-3515.
A high α-selectivity of a ligand controlled selective hydroborylation of terminal alkynes to α-vinylboronates using a Pd catalyst can be switched to furnish β-vinylboronates by altering the ligand from a trialkylphosphine to N-heterocyclic carbene. Various terminal alkynes furnish the corresponding α- or β-vinylboronates in excellent selectivity and yield.
D. P. Ojha, K. R. Prabhu, Org. Lett., 2016, 18, 432-435.
Reliable, operationally simple, catalytic α-selective hydroalumination reactions proceed in the presence of diisobutylaluminum hydride and (Ni(dppp)Cl2), and, unlike uncatalyzed transformations, generate little or no alkynylaluminum byproducts. The derived α-vinyl halides and boronates can be synthesized through direct treatment with the appropriate electrophiles.
F. Gao, A. H. Hoveyda, J. Am. Chem. Soc., 2010, 132, 10961-10963.
A boryl-Heck reaction of terminal alkenes with commercially available catecholchloroborane (catBCl) as an electrophilic boron reagent provides trans-alkenyl boronic esters. In situ transesterification allows for rapid access to various boronic esters, amides, and other alkenyl boron adducts.
W. B. Reid, J. J. Spillane, S. B. Krause, D. A. Watson, J. Am. Chem. Soc., 2016, 138, 5539-5542
In a copper-catalyzed formal carboboration of alkynes, a C-B bond and a C-C bond are created in a single catalytic cycle. The reaction proceeds with high regioselectivity and syn-stereoselectivity to form tri- and tetrasubstituted vinylboronic esters from commercially available bis(pinacolato)diboron. A subsequent cross-coupling reaction gives access to highly substituted alkenes.
R. Alfaro, A. Parra, J. Alemán, J. L. G. Ruano, M. Tortosa, J. Am. Chem. Soc., 2012, 134, 15165-15168.
In a copper-catalyzed regio- and stereoselective borylalkylation of dialkylsubstituted internal alkynes with bis(pinacolato)diboron and alkyl halides, a borylcopper species containing a novel π-accepting N-heterocyclic carbene ligand chemoselectively reacted with unactivated internal alkynes over alkyl halides. The intermediate alkenylcopper species subsequently reacted with alkyl halides, affording the desired products.
T. Itoh, Y. Shimizu, M. Kanai, J. Am. Chem. Soc., 2016, 138, 7528-7531.
Protoborations of terminal allenes catalyzed by NHC-Cu complexes afford valuable 1,1- or trisubstituted vinylboronates with high site selectivity and stereoselectivity. The scope of the method, application to natural product synthesis, and mechanistic details for the observed selectivity are presented.
F. Meng, B. Jung, F. Haeffner, A. H. Hoveyda, Org. Lett., 2013, 15, 1414-1417.
The catalytic property of nanoporous gold for activation of bis(pinacolato)diboron allows an efficient direct diboration of alkynes in a heterogeneous process. The nanoporous gold catalyst is able to cleave the B–B bond of bis(pinacolato)diboron without using any additives.
Q. Chen, J. Zhao, Y. Ishikawa, N. Asao, Y. Yamamoto, T. Jin, Org. Lett., 2013, 15, 5766-5769.
A cobalt-catalyzed method for the diboration of terminal alkynes with B2Pin2 proceeds efficiently at 23°C with excellent 1,1-selectivity and broad functional group tolerance. With the unsymmetrical diboron reagent PinB-BDan, stereoselective 1,1-diboration provided products with two boron substituents that exhibit differential reactivity.
S. Krautwald, M. J. Bezdek, P. J. Chirik, J. Am. Chem. Soc., 2017, 139, 3868-3875.
Substituted alkynoates undergo borylation in a regio-, stereo-, and chemoselective fashion to afford (Z)-β-boryl-α,β-unsaturated esters in the presence of bis(pinacolato)diboron and catalytic amounts of both copper(II) and 4-picoline. The reaction is performed under mild conditions using water as solvent and open to the atmosphere.
C. L. Peck, J. A. Calderone, W. L. Santos, Synthesis, 2015, 47, 2242-2248.
4-Substituted 1,2-oxaborol-2(5H)-ols were prepared through copper-catalyzed carbomagnesation of propargyl alcohol, followed by the transmetallation of magnesium to boron in a one-pot procedure. The Suzuki-Miyaura cross-coupling of these new 2,2-disubstituted alkenylboronic acids with aryl halides afforded stereodefined 2,3-disubstituted allyl alcohols in good to excellent yields.
G.-H. Fang, Z.-J. Yan, M.-Z. Deng, Synthesis, 2006, 1148-1154.
A new method for the synthesis of organoborates starting from α,β-unsaturated acetals was developed. The available alkoxy-functionalized butadienyl- and styrylboronic esters cross couple effectively with a broad spectrum of aryl halides under mild conditions. This method provides an effective approach to aromatic ketones.
P. B. Tivola, A. Deagostino, C. Prandi, P. Venturello, Org. Lett., 2002, 4, 1275-1277.
The Cross-coupling reaction of bis(pinacolato)diboron with β-(trifluoromethanesulfonyloxy)-α,β-unsaturated carbonyl compounds was carried out in the presence of PdCl2(PPh3)2-2PPh3 (3 mol%) and KOPh in toluene or K2CO3 in dioxane for the synthesis of cyclic and acyclic β-boryl-α,β-unsaturated esters, amides, and ketones in high yields.
J. Takagi, A. Kamon, T. Ishiyama, N. Miyaura, Synlett., 2002, 1880-1882.
Monobenzofused 1,4-azaborine phosphine ligands uniquely support Pd-catalyzed trans-selective hydroboration of terminal and internal 1,3-enynes to furnish the corresponding dienylboronates in high efficiency and diastereoselectivity.
S. Xu, Y. Zhang, B. Li, S.-Y. Liu, J. Am. Chem. Soc., 2016, 138, 14566-14569.
Alkynylboration of alkynes with alkynyl(pinacol)boranes in the presence of nickel catalysts gave cis-1-borylbut-1-en-3-yne derivatives. Some boryl-substituted enynes were reacted with sp2 halides under Suzuki-Miyaura coupling conditions.
M. Suginome, M. Shirakura, A. Yamamoto, J. Am. Chem. Soc., 2006, 128, 14438-14439.
In the presence of a chiral phosphoramidite ligand, the palladium-catalyzed diboration of allenes can be executed with high enantioselectivity with a range of aromatic and aliphatic allenes. A mechanism is proposed based on isotopic-labeling experiments, stereodifferentiating reactions, kinetic analysis, and computational experiments.
H. E. Burks, S. Liu, J. P. Morken, J. Am. Chem. Soc., 2007, 129, 8766-8773.
Pd-catalyzed diboration of prochiral allenes occurs exclusively at the internal position and is accelerated in the presence of Lewis basic ligands. A chiral ligand was employed, and the enantiomeric excess of a variety of diboration products was found to be in the range of 86-92% ee.
N. F. Pelz, A. R. Woodward, H. E. Burks, J. D. Sieber, J. P. Morken, J. Am. Chem. Soc., 2004, 126, 16328-16329.
Bromoboration of propyne with BBr3 proceeds in syn-selectivity to produce (Z)-2-bromo-1-propenyldibromoborane, which is prone to stereoisomerization. Treatment with pinacol yields the stable and storable pinacolboronate. Negishi coupling gives trisubstituted (Z)-alkenylpinacolboronates in good yields. Iodinolysis of the boronates affords alkenyl iodides in good yields.
C. Wang, T. Tobrman, Z. Xu, E.-i. Negishi, Org. Lett., 2009, 11, 4092-4095.
A stereoselective synthesis of tetrasubstituted alkenylboronates, which are useful synthetic intermediates for further functionalizations, was established via the lithiation/nucleophilic addition reaction of 1,1-organodiboronates to carbonyl compounds.
K. Endo, M. Hirokami, T. Shibata, J. Org. Chem., 2010, 75, 3469-3472.
A highly stereoselective boron-Wittig reaction between stable and readily accessible 1,1-bis(pinacolboronates) and aldehydes furnishes various synthetically useful di- and trisubstituted vinyl boronate esters.
J. R. Coombs, L. Zhang, J. P. Morken, Org. Lett., 2015, 17, 1708-1711.
A number of alkynyl pinacolboronates were stereoselectively reduced to the cis-alkenyl pinacolboronates via hydroboration with dicyclohexylborane followed by chemoselective protodeboronation using acetic acid. Treatment with potassium hydrogen fluoride smoothly converted these to the corresponding potassium organotrifluoroborates.
G. A. Molander, N. M. Ellis, J. Org. Chem., 2008, 73, 6841-6844.
The cobalt-catalyzed Diels-Alder reaction of alkynyl pinacol boronic esters with various dienes generates cycloadducts in very good regioselectivity. A reaction sequence (Diels-Alder reaction, Suzuki coupling, DDQ oxidation) was successfully performed as a one pot operation without isolation of the intermediates.
G. Hilt, K. I. Smolko, Angew. Chem. Int. Ed., 2003, 42, 2795-2797.
In situ generation of allylic boronates by iridium-catalyzed borylation of cyclic alkenes in the presence of additives, such as methylimidazole and DBU, followed a reaction with aldehydes allows the synthesis of stereodefined homoallylic alcohols. Cycloalkenes without additives as well as acyclic substrates gave vinylic boronates, which were coupled with organohalides in a Suzuki-Miyaura sequence.
V. J. Olsson, K. J. Szabó, J. Org. Chem., 2009, 74, 7715-7723.
1-Alkenylboronic acid pinacol esters have been synthesized via a palladium-catalyzed cross-coupling reaction of bis(pinacolato)diboron with 1-alkenyl halides or triflates in toluene at 50°C in the presence of KOPh in high yields with complete retention of configuration of the double bonds. A one-pot synthesis of unsymmetrical 1,3-dienes via the borylation-coupling sequence has been developed.
J. Takagi, K. Takahashi, T. Ishiyama, N. Miyaura, J. Am. Chem. Soc., 2002, 124, 8001-8006.
The presence of supported gold nanoparticles enables gold-catalyzed silaboration of terminal alkynes with PhMe2SiBpin. The reaction proceeds at ambient conditions in very good yields with a regioselectivity opposite to that observed in the presence of Pd or Pt catalysts. The abnormal regioselectivity is attributed to steric factors imposed by the Au nanoparticle during the 1,2-addition of silylborane to the alkyne.
C. Gryparis, M. Stratakis, Org. Lett., 2014, 16, 1430-1433.
Pd-catalyzed enantioselective diborations of prochiral allenes followed by allylation reactions with primary imines provide vinyl boronates which may be oxidized to give nonracemic Mannich products. Alternatively, enantiomerically enriched homoallylic amine derivatives may be obtained by protonation and Suzuki cross-coupling of the vinyl boronate.
J. D. Sieber, J. P. Morken, J. Am. Chem. Soc., 2006, 128, 74-75.