Categories: C-B Bond Formation > Synthesis of boronic acids and boronates >
Synthesis of vinylboronic acids and vinylboronates
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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.
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.
Preparation of (E)-1-Alkenylboronic Acid Pinacol Esters via Transfer of
Alkenyl Group from Boron to Boron
K. Shirakawa, A. Arase, M. Hoshi, Synthesis,
2004,
1814-1820.
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.
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.
A Cu(O-t-Bu)-Xantphos catalyst system was effective for the preparation
of various allenylboronates with different substitution patterns, those with
functional groups, and an axially chiral one. A Lewis acid promoted
stereoselective addition of allenylboronates to aldehydes leads to
homopropargylic alcohols.
H. Ito, Y. Sasaki, M. Sawamura, J. Am. Chem. Soc., 2008,
130, 15774-15775.
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.
Related
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 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.
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.
