Synthesis of benzylboronic acids and benzylboronates
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.
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.
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.
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.
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.