Categories: C-B Bond Formation > Synthesis of boronic acids and boronates >
Synthesis of benzylboronic acids and benzylboronates
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A catalytic amount of Mg as the only metal enables a reductive coupling between
benzyl halides and pinacolborane. HBpin acts both as an electrophile and as a
reducing agent to regenerate an organomagnesium species in situ. An hydride
oxidation mechanism is proposed on the basis of DFT calculations.
C. Pintaric, S. Olivero, Y. Gimbert, P. Y. Chavant, E. Duņach, J. Am. Chem. Soc., 2010,
132, 11825-11827.
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.
Electroreductive conditions enable a transformation of benzylic and allylic
alcohols, aldehydes, and ketones into boronic esters in the presence of readily
available pinacolborane, which serves both as an activator and an electrophile.
This strategy is applicable to a variety of substrates and can be employed for
the late-stage functionalization of complex molecules.
W. Guan, Y. Chang, S. Lin, J. Am. Chem. Soc.,
2023, 145, 16966-16972.
Iodine catalyzes a direct borylation of benzylic alcohols. This
transition-metal-free borylation tolerates various functional
groups and provides useful benzylic boronate esters from widely available
benzylic alcohols. Preliminary mechanistic investigations indicated that
benzylic iodide and radicals are involved as the key intermediates.
C. Yin, L. Luo, H. Zhang, Org. Lett., 2023, 25,
1701-1705.
An iron-catalyzed benzylic C-H borylation reaction offers unique selectivity
in the presence of an amide-based directing group. The reaction targets primary
and secondary C(sp3)-H bonds to deliver high-value boronic esters
under mild conditions with short reaction times. Functional groups are well
tolerated, and complete site selectivity is observed in the presence of multiple
benzylic C-H bonds.
H. Lee, T. He, S. P. Cook, Org. Lett., 2023, 25,
1-4.
A chiral nickel complex catalyzes a facile enantioselective hydroboration of
vinylarenes to provide chiral benzylic boronate esters. Various vinylarenes
react with bis(pinacolato)diboron in the presence of MeOH as a hydride source to
form chiral boronate esters in good yields with high ee. Me4NF
activates B2pin2 for ensuring fast transmetalation to
achieve high enantioselectivities.
H. N. Tran, L. M. Stanley, Org. Lett., 2022, 24,
395-399.
A regioselective hydroboration of vinylarenes catalyzed by a Rh(I)-DPPB complex
proceeded rapidly when DMAP was used as an additive to furnish the desired
boronates in good to excellent yield with high regioselectivity.
K. Endo, M. Hirokami, K. Takeuchi, T. Shibata, Synlett, 2008,
3231-3233.
An inexpensive and air-stable cobalt(II) coordination polymer catalyzes
a highly efficient and practical hydroboration of alkenes in the presence of KOtBu within minutes with low catalyst loading. For a range of
vinylarenes, unusual Markovnikov selectivity was observed.
G. Zhang, J. Wu, S. Li, S. Cass, S. Zheng, Org. Lett.,
2018, 20, 7893-7897.
A chiral imidazoline iminopyridine (IIP) ligand enables a highly regio- and
enantioselective cobalt-catalyzed hydroboration/hydrogenation of internal
alkynes with HBpin in the presence of hydrogen. Primary mechanistic studies show
that a cobalt-catalyzed regioselective hydroboration of alkynes is followed by a
HBpin-promoted and cobalt-catalyzed enantioselective hydrogenation of
alkenylboronates.
J. Guo, B. Cheng, X. Shen, Z. Lu, J. Am. Chem. Soc., 2017,
139, 15316-15319.
A reductive three-component coupling of terminal alkynes, aryl halides,
and pinacolborane provides benzylic alkyl boronates in good yields via a hydrofunctionalization of both
π-bonds of the alkyne promoted by cooperative action of the catalysts. The
reaction offers excellent substrate scope and tolerates the presence
of esters, nitriles, alkyl halides, epoxides, acetals and alkenes.
M. K. Armstrong, G. Lalic, J. Am. Chem. Soc.,
2019,
141, 6173-6179.
(PPh3)3CoH(N2) is an effective catalyst for the
hydroboration of alkenes. In alkene isomerization-hydroboration, (PPh3)3CoH(N2)
promotes boron incorporation adjacent to π-systems even in substrates where the
alkene is at a remote position.
M. L. Scheuermann, E. J. Johnson, P. J. Chirik, Org. Lett.,
2015,
17, 2708-2711.
CsF with 1.1 equiv of H2O effects highly efficient
protodeboronation on tertiary diarylalkyl boronic esters with essentially
complete retention of configuration, whereas TBAF·3H2O can be used
for tertiary aryldialkyl boronic esters. Furthermore, substituting D2O
for H2O provides ready access to deuterium-labeled enantioenriched
tertiary alkanes. A short synthesis of the sesquiterpene (S)-turmerone is
described.
S. Nave, R. P. Sonawane, T. G. Elford, V. K. Aggarwal, J. Am. Chem. Soc., 2010,
132, 17096-17098.
Alkali metals promote a general reductive 1,2-diborations and
1,2-dicarbofunctionalizations of alkenes by employing trimethoxyborane and
strained cyclic ethers such as oxirane and oxetane. In addition, unsymmetrical
carbo- or thioborations have been accomplished via treatment with
trimethoxyborane followed by carbon or sulfur electrophiles.
M. Fukazawa, F. Takahashi, K. Nogi, T. Sasamori, H. Yorimitsu,
Org. Lett., 2020, 22, 2303-2307.
A copper-catalyzed enantioselective hydroboration of α,β-unsaturated aldehydes
with pinacolborane provides the corresponding γ-pinacolboronate alcohols in good
yields and enantioselectivities through consecutive hydroboration of the C=O and
C=C bonds. The resulting γ-pinacolboronate alcohols could be utilized in various
transformations.
W. J. Jang, S. M. Song, Y. Park, J. Yun, J. Org. Chem., 2019, 84,
4429-4434.
Cu[(S)-(R)-ppfa]Cl and AgNTf2 as catalyst enable an
asymmetric conjugate addition of B2pin2 onto
α-functionalized α,β-unsaturated carbonyl compounds under mild, neutral
conditions in the presence of an alcohol. AgNTf2 and alcohols play
crucial roles for achieving high catalytic activity and enantio- and
diastereoselectivity.
J.-B. Xie, S. Lin, S. Qiao, G. Li, Org. Lett.,
2016, 18, 3926-3929.
A single chiral sulfoxide-(dialkyl)phosphine (SOP) ligand enables a highly
efficient and enantioselective copper(I)-catalyzed pinacolboryl addition to N-Boc-imines
providing both enantiomeric isomers of α-amino boronic esters depending on an
achiral counteranion switch.
D. Wang, P. Cao, B. Wang, T. Jia, Y. Lou, M. Wang, J. Liao, Org. Lett.,
2015,
17, 2420-2423.
Pd/Cu-catalyzed coupling and boration of acyl chlorides with alkynes and B2pin2
provide the corresponding saturated β-boryl ketones in the presence of ethyl
acetate as the hydrogen source. Various β-boryl ketones were synthesized in very
good yields with broad functional group tolerance.
F. Zhu, P. Yin, J. Org. Chem., 2023, 88,
4352-4358.
Related
The use of an equimolar amount of base with a diborylmethane enabled a
chemoselective Pd-catalyzed Suzuki–Miyaura cross-coupling reaction for the
synthesis of various benzylboronate derivatives in very good yields. Reactions
of sterically hindered aryl bromides can give products in good yields.
K. Endo, T. Ohkubo, T. Shibata, Org. Lett., 2011,
13, 3368-3371.
In the presence of a chiral monodentate taddol-derived phosphoramidite ligand,
catalytic enantiotopic-group-selective cross-couplings of achiral geminal
bis(pinacolboronates) provide a route for the construction of nonracemic chiral
organoboronates with high levels of asymmetric induction. Mechanistic
experiments suggest that the reaction occurs by a stereochemistry-determining
transmetalation with inversion of configuration at carbon.
C. Sun, B. Potter, J. P. Morken, J. Am. Chem. Soc., 2014,
136, 6534-6537.
An efficient α-deprotonation and functionalization of benzylboronates with
a wide range of electrophiles offers
high atomic efficiency and an alternative C-C bond disconnection for the
synthesis of benzylboronates. Notably, the boryl
group enables high diastereoselectivities when unsymmetrical secondary
α-bromoesters are used.
H. Jin, J. Han, X. Liu, C. Feng, M. Zhan, Org. Lett., 2023, 25,
4168-4172.
A visible-light-induced, nickel-catalyzed, chemoselective cross-coupling
reaction between gem-borazirconocene alkanes and diverse aryl halides
provides a wide range of alkyl Bpin derivatives in high yields with excellent
regioselectivity. This practical method features attractively simple reaction
conditions and a broad substrate scope.
C. Yang, Y. Gao, S. Bai, C. Jiang, X. Qi, J. Am. Chem. Soc.,
2020, 142, 11506-11513.
Catalytic enantioselective conjunctive cross-couplings that employ Grignard
reagents provide chiral organoboronic esters in an efficient and highly
selective fashion. The use of sodium triflate enables "ate" complex formation
and overcomes catalytic inhibition by halide ions.
G. J. Lovinger, M. D. Aparece, J. P. Morken, J. Am. Chem. Soc., 2017,
139, 3153-3160.
α-Halogenated boronic esters are versatile building blocks. A convenient
visible light-induced C-H bromination reaction of readily available benzyl
boronic esters provides α-brominated boronates in high yields under mild
conditions and with good functional group tolerance. The analogous chlorides and
iodides can be accessed via Finkelstein reaction.
F.-C. Gao, M. Li, H.-Y. Gu, X.-Y. Chen, S. Xu, Y. Wei, K. Hong, J. Org. Chem., 2023, 88,
14246-14254.
A palladium-catalyzed chemoselective Negishi cross-coupling of a
bis[(pinacolato)boryl]methylzinc halide with aryl (pseudo)halides provides an
array of benzylic 1,1-diboronate esters, which can serve as useful synthetic
handles for further transformations. The developed coupling reaction is
compatible with various functional groups and can be easily scaled up.
H. Lee, Y. Lee, S. H. Cho,
Org. Lett., 2019, 21, 5912-5916.
A general method for accessing sterically encumbered geminal bis(boronates) is
based on a formal umpolung strategy. Readily available 1,1-diborylalkanes were
first converted into the corresponding α-halogenated derivatives, which then
serve as electrophilic components, undergoing a formal substitution with a
diverse array of nucleophiles to form a series of C−C, C−O, C−S, and C−N bonds.
P.-F. Ning, Y. Wei, X.-Y. Chen, Y.-F. Yang, F.-C. Gao, K. Hong, Angew. Chem.
Int. Ed., 2023, 62,
e202315232.