Chinese

Journal of Catalysis 39 (2018) 1725–1729 

available at www.sciencedirect.com 

journal homepage: www.elsevier.com/locate/chnjc 

Communication 
Cu‐catalyzed deoxygenative gem‐hydroborylation of aromatic
aldehydes and ketones to access benzylboronic esters
Lu Wang a, Wei Sun a,b, Chao Liu a,*
a State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou Research Institute of Lanzhou Institute of Chemical Physics (LICP), LICP,
Chinese Academy of Sciences, Lanzhou 730000, Gansu, China
b University of Chinese Academy of Sciences, Beijing 100049, China

 
A R T I C L E I N F O A B S T R A C T

Article history:   Organoboron compounds are widely used in synthetic chemistry, pharmaceutical chemistry and
Received 13 June 2018 material chemistry. Among various organoboron compounds, benzylboronic esters are unique and
Accepted 15 July 2018 highly reactive, making them suitable benzylation reagents. At present, the synthetic methods for
Published 5 November 2018 the syntheses of benzylboronic esters are still insufficient to meet their demands. It is necessary to
develop novel and practical methods for their preparation. In this work, a novel copper‐catalyzed
Keywords:   deoxygenative gem‐hydroborylation of aromatic aldehydes and ketones has been developed. This
Homogeneous catalysis direct and operationally simple protocol provides an effective approach for the synthesis of a varie‐
Copper catalysis ty of primary and secondary benzylboronates, in which broad functional group tolerance was pre‐
Deoxygenative gem‐hydroborylation sented. Widely available B2pin2 (pin = pinacol) was used as the boron source and alcoholic proton
Aromatic aldehydes was applied as the hydride source.
Aromatic ketones © 2018, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.

 
Organoboron compounds represent significant structural Pd, Cu, Ni, Fe, et al.) catalyzed borylation of benzyl (pseu‐
motifs in organic synthesis [1–6], developing novel and practi‐ do)halides has been reported for the synthesis of benzyl‐
cal strategies for the synthesis of organoboron compounds is boronic esters [14,16–22]. Moreover, the cross‐coupling of aryl
highly demanding in nowadays chemical society. Among vari‐ halides [23,24] or sulfonates [25] with 1,1‐diborylalkanes un‐
ous organoboron compounds, benzylboronic esters are unique der palladium catalysis is also an effective method. Benzylic
alkylboron compounds. They are relatively reactive and can be alcohols have also been utilized as electrophiles for the synthe‐
a practical benzylation reagent in the presence of transition sis of primary benzylic boronic esters in the presence of palla‐
metal catalysts [7–14]. Up to date, tremendous efforts have dium or copper catalyst [26,27], in which secondary benzylic
been made for the synthesis of benzylboronic esters. In general, alcohols cannot be compatible in those catalytic system. Di‐
benzylboronic esters are often synthesized by the borylation of rectly utilizing benzylic C–H as the electrophile under the tran‐
Grignard or lithium reagents [15]. However, this method shows sition metal catalyzed borylation condition is an ideal ap‐
poor functional group compatibility and the difficult prepara‐ proach, while it currently still suffers from the chemoselectivity
tion of benzylic Grignard and lithium reagents make this classic issues on benzylic or aromatic C–H borylation and mono‐ or
approach less practical. Recently, transition metal (including di‐borylation [28–30]. Styrenes could also be used for the syn‐

* Corresponding author. E‐mail: chaoliu@licp.cas.cn

This work was supported by the National Natural Science Foundation of China (91745110, 21673261, 21603245, 21633013, 21703265) and a
Start‐up funding from LICP. Support from the Young Elite Scientist Sponsorship Program by CAST, CAS Interdisciplinary Innovation Team, the Key
Program of CAS (QYZDJ–SSW–SLH051), the Youth Innovation Promotion Association CAS (2018458) and the ‘Light of West China’ Program.
DOI: 10.1016/S1872‐2067(18)63139‐0 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 39, No. 11, November 2018
1726 Lu Wang et al. / Chinese Journal of Catalysis 39 (2018) 1725–1729

B2 pin2 (2.2 equiv.)

This Work ICyCuCl (5 mol%)
R NaOtBu (1.3 equiv.)
MeOH (1.0 equiv.) Bpin
Ar O
Ar M O
NNHTs Hexane, 100 C, 5 h
M = MgX, Li
Ar R 1a 2a, 71%  
Scheme 2. The deoxygenative gem‐hydroborylation of benzaldehyde.

R yields. For instance, the reaction of substrates with elec‐

Ar Bpin tron‐donating groups (‒OMe, ‒tBu or other oxygen‐containing
groups) and substrates with electron‐withdrawing groups (‒F
R and ‒Cl) all proceeded well, affording the corresponding prod‐
Ar X
ucts in moderate to good yields (2b–2e, 2g, 2i–2m). The sul‐
+ Ar fur‐containing group ‒SMe was also tolerated under standard
X = Cl, Br, I, OTs, NMe3 , OH, H...
ArX condition (2f). It was noteworthy that steric effect did not have
X = Br, I a strong influence on the reactivity. For instance, when
Scheme 1. Strategies for the synthesis of benzylboronic esters.
2,4,6‐trimethylbenzaldehyde was used as the substrate, the
corresponding product 2h was isolated in 52% yield. Moreo‐
ver, other aromatic aldehyde such as 2‐naphthaldehyde and
thesis of benzylboronic esters via unusual transition metal cat‐ hetero‐aromatic aldehyde such as 2‐thenaldehyde proceeded
alyzed Markovnikov selective hydroborations [31–37]. smoothly to generate the corresponding products (2n, 2o).
Through 1,2‐metelate rearrangement, benzylboronic esters However, when extending the catalytic system to aromatic
could be synthesized from tosylhydrazones and HBpin or ketones, problem occurred and only trace amounts of products
B2pin2 under a metal‐free condition [38]. Tosylhydrazones are were detected, in which most of the starting ketones were re‐
usually prepared from carbonyl compounds. The direct utiliza‐ duced to their corresponding alcohols. The generation of alco‐
tion of aromatic carbonyls for the synthesis of benzylboronic hols indicated the presence of hydride species in this catalytic
esters would be more step‐economy [39]. Herein, we describe system. It has been demonstrated that proton could be used as
the first deoxygenative gem‐hydroborylation of aromatic alde‐ hydride source in the presence of B2pin2 [41–49]. Furthermore,
hydes and ketones under copper catalysis to access both pri‐ Clark et al. [50] has shown that the addition rate of a cop‐
mary and secondary benzylboronic esters (Scheme 1). per‐boron species to ketone C=O group was slower than that of
In 2017, we have demonstrated a deoxygenative aldehydes. Therefore, the addition of hydride species to ketone
gem‐diborylation of aliphatic aldehydes and ketones [40]. Dur‐ carbonyls dominated the transformation of ketones. As a result,
ing this study, when benzaldehyde (1a) was utilized as the alcohols were produced as the major products. In order to
substrate, a significant amount of gem‐hydroborylation product solve this problem, a more reactive KOtBu was applied to acti‐
benzylboronic ester (2a) was obtained instead of gem‐diboron vate B2pin2 instead of NaOtBu, for which we expected to in‐
product. These initial results promoted us to further improve crease the nucleophilicity of boryl group for the addition to
the preparative procedure by using MeOH as the [H] source for ketone carbonyl groups. Meanwhile, a less acidic alcohol was
achieving the catalytic synthesis of benzylboronic esters from utilized as the proton source instead of MeOH, for which we
aromatic aldehydes. As a result, 2a was isolated with 71% yield expected to slower down the generation of hydride species. To
under an optimal catalysis system: ICyCuCl (5 mol%), B2pin2 our delight, after a series of attempts, when the reaction was
(2.2 equiv.), NaOtBu (1.3 equiv.), with MeOH (1.0 equiv.) as the carried out in the presence of 1.0 equiv. KOtBu as base and
proton source in hexane at 100 °C for 5 h (Scheme 2). EtOH as the proton source, the aromatic ketones were success‐
With the optimized conditions in hand, a wide range of ar‐ fully transformed to their corresponding secondary benzyl‐
omatic aldehydes were first examined for its generality in this boronic esters.
transformation. As shown in Scheme 3, the reaction system is Subsequently, a series of aromatic ketones were investigat‐
efficient for substrates containing various functional groups ed under the optimized conditions (Scheme 4). Aromatic ke‐
and afford the corresponding products in moderate to good tones, such as acetophenone, propiophenone and butyrophe‐

Chao Liu (Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences (CAS)) received
the Catalysis Rising Star Award in 2017, which was presented by The Catalysis Society of Chi‐
na. Chao Liu (1985) obtained his B.Sc (2007) and Ph.D. (2012) at Wuhan University under the
supervision of Prof. Aiwen Lei. After his postdoctoral research at Wuhan University, he started his
independent career in 2015 at Suzhou Research Institute of LICP, Lanzhou Institute of Chemical
Physics (LICP), CAS. He is a member of the Youth Innovation Promotion Association, CAS and was
selected for the Young Elite Scientist Sponsorship Program by CAST. His group is now focusing on
organoboron chemistry and carbonyl chemistry.
 Lu Wang et al. / Chinese Journal of Catalysis 39 (2018) 1725–1729 1727

Scheme 5. Two proposed pathways for the deoxygenative

gem‐hydroborylation of aldehydes and ketones.

was also a suitable substrate to produce the corresponding

product in moderate yields (4h).
Mechanistically, the copper‐catalyzed 1,2‐borylation of car‐
bonyl was believed to initiate the reaction, in which ‐OBpin
benzylboronic ester was generated. Our previous report and
Scheme 3. Deoxygenative gem‐hydroborylation of aldehydes. Reaction
conditions: 1 (0.5 mmol), B2pin2 (1.1 mmol), MeOH (0.5 mmol), ICyCuCl the results from the monitor of the reaction course demon‐
(0.025 mmol), NaOtBu (0.65 mmol), hexane (2.0 mL), 100 °C, 5 h. Iso‐ strated above exhibited that the borylation of ‐OBpin to give
lated yields. 1H NMR yields are shown in the parentheses using CH2Br2 benzylic gem‐diboron followed by protonation with alcohol is
as the internal standard, decomposition of products occurred through most likely the reaction mechanism (Scheme 5, Path A) [38,40].
column chromatography.
In this case, the ‐OBpin containing tetracoordinated boron
species with boryl as the migrating group was constructed.
none, could be smoothly transformed to the corresponding However, another pathway is also possible. As demonstrated
benzylboronic esters in moderate yields (4a, 4b, 4d, 4e). Sub‐ above, there might be hydride species presented in the reaction
strates bearing electron‐rich group, such as system. Therefore, a tetracoordinated boron species with hy‐
p‐methoxyacetophenone, have been evaluated and the desired dride as the migrating group would also generate the desired
product was obtained in moderate yield albeit prolonged reac‐ deoxygenative gem‐hydroborylation product (Scheme 5, Path
tion time was required (4c, 4i). A significant amount of B).
1,1‐diborylation products was detected by GC‐MS if the reac‐ To verify Path A, the benzylic gem‐diboron 4a‐1 was syn‐
tion time was shortened to 1 h. This interesting phenomenon thesized according to the literature [51]. Then it was subjected
indicated that the ketones may firstly transformed to to react with EtOH in the presence of KOtBu. As a result, the
1,1‐diborylakanes, followed by selective protodeboronation to protodeborylation product 4a was obtained in 99 % yield (de‐
afford the final products. Benzocycloanone can be smoothly termined by 1H NMR analysis). In this case, catalytic amount of
converted into the desired products (4f, 4g). 2‐Acetonaphthone KOtBu was used as the promotor, because of the KOtBu was
almost consumed in those standard reaction systems. This re‐
ICyCuCl (20 mol%) sult indicated that the benzylic gem‐diboron was presumed to
KOtBu (1.0 eq.) R'
ArCOR' + B2pin2 + EtOH
toluene (1 mL)
be an intermediate in this transformation (Scheme 6, Eq. (1)).
Ar Bpin
3 2.5 eq. 1.0 eq. 100 C 4 Next, in order to verify Path B, ‐OBpin benzylboronate 2a‐1
was synthesized from benzaldehyde according to the literature
Bpin Bpin Bpin [52]. Then it was subjected to react with MeOH, NaOtBu and
B2pin2 in hexane at 100 °C for 5 h. As a result, the desired 2a
MeO
4c, 33%(62%) was obtained in 47% yield, indicating the generation of
4a, 77%(78%) 4b, 57%(70%)
(48 h)
Bpin Bpin Bpin EtOH (1.0 eq.)
Bpin
Bpin KOt Bu (10 mol%) (1)
Ph Bpin
Ph toluene, 100 C
4a-1 1h 4a, 99%
4d, 30%(75%) 4e, 37% 4f, 74%(78%) MeOH (1.0 eq.)
Bpin Bpin Bpin B2pin 2 (1.0 eq.)
OBpin
O NaO tBu (1.2 eq.) (2)
Ph Bpin
Ph Bpin Hexane, 100 C
O 2a, 47%
2a-1 5h
4i, 21%(46%)
4g, 39%(54%) 4h, 51%(82%) HBpin (1.0 eq.)
(48 h) OBpin
NaO tBu (1.2 eq.)
Scheme 4. Deoxygenative gem‐hydroborylation of ketones. Reaction Ph Bpin Ph Bpin (3)
conditions: 3 (0.5 mmol), B2pin2 (1.25 mmol), EtOH (0.5 mmol), ICyCuCl 2a-1 Hexane, 100 C
2a, 57%
(0.1 mmol), KOtBu (0.5 mmol), toluene (1.0 mL), 100 oC, 1‒48 h. Isolat‐ 5h  
ed yields. 1H NMR yields are shown in the parentheses using CH2Br2 as Scheme 6. Control experiments.
the internal standard.
1728 Lu Wang et al. / Chinese Journal of Catalysis 39 (2018) 1725–1729

‐OBpin benzylboronate as an intermediate in this transfor‐ 14085–14089.

mation (Scheme 6, Eq. (2)). Furthermore, HBpin was applied as [9] K. Miyazawa, Y. Yasu, T. Koike, M. Akita, Chem. Commun., 2013, 49,
the hydride source to test the hydride‐migration hypothesis 7249–7251.
[10] R. D. Grigg, J. W. Rigoli, R. Van Hoveln, S. Neale, J. M. Schomaker,
(Scheme 6, Eq. (3)). 2a‐I was converted to the desired 2a
Chem. Eur. J., 2012, 18, 9391–9396.
smoothly in the presence of HBpin and NaOtBu in 57% yield.
[11] J. C. Tellis, D. N. Primer, G. A. Molander, Science, 2014, 345,
This result indicated that the hydride‐migration pathway is
433–436.
also possible for this transformation. Using CD3OD and HBpin [12] G. A. Molander, N. Ellis, Acc. Chem. Res., 2007, 40, 275–286.
resulted in a mixture of deuterated‐2a and 2a (See supporting [13] V. Bagutski, T. G. Elford, V. K. Aggarwal, Angew. Chem. Int. Ed.,
information for details), also indicated the possibilities of both 2011, 50, 1080–1083.
pathways for this transformation. At current stage, either [14] A. Bej, D. Srimani, A. Sarkar, Green Chem., 2012, 14, 661–667.
pathway could not be ruled out. [15] A. Pelter, K. Smith, H. C. Brown, Borane reagents, Academic Press,
In summary, we have developed a straightforward and ef‐ Newyork, 1998.
fective method for the synthesis of benzylboronic esters [16] S. K. Bose, S. Brand, H. O. Omoregie, M. Haehnel, J. Maier, G. Bring‐
through Cu‐catalyzed deoxygenative gem‐hydroborylation of mann, T. B. Marder, ACS Catal., 2016, 6, 8332–8335.
[17] C. T. Yang, Z. Q. Zhang, H. Tajuddin, C. C. Wu, J. Liang, J. H. Liu, Y. Fu,
readily available aromatic aldehydes and ketones. A series of
M. Czyzewska, P. G. Steel, T. B. Marder, L. Liu, Angew. Chem. Int.
substituted aryl aldehydes and ketones were successfully con‐
Ed., 2012, 51, 528–532.
verted to their corresponding products. Alcoholic proton was
[18] T. C. Atack, R. M. Lecker, S. P. Cook, J. Am. Chem. Soc., 2014, 136,
utilized as the hydride source. At current stage, either boryl 9521–9523.
migration followed by protodeborylation or hydride migration [19] A. S. Dudnik, G. C. Fu, J. Am. Chem. Soc., 2012, 134, 10693–10697.
is possible for the mechanistic consideration. Further detailed [20] J. Hu, H. Sun, W. Cai, X. Pu, Y. Zhang, Z. Shi, J. Org. Chem., 2016, 81,
mechanism is currently underway in our laboratory. 14–24.
[21] A. Giroux, Tetrahedron Lett., 2003, 44, 233–235.
References [22] R. B. Bedford, P. B. Brenner, E. Carter, T. Gallagher, D. M. Murphy,
D. R. Pye, Organometallics, 2014, 33, 5940–5943.
[1] D. G. Hall, Boronic Acids: Preparation and Applications in Organic [23] K. Endo, T. Ohkubo, M. Hirokami, T. Shibata, J. Am. Chem. Soc.,
Synthesis, Medicine and Materials, 2nd completely rev. ed., 2010, 132, 11033–11035.
Wiley‐VCH, Weinheim, 2011. [24] K. Endo, T. Ohkubo, T. Shibata, Org. Lett., 2011, 13, 3368–3371.
[2] D. H. Tan, E. Lin, W. W. Ji, Y. F. Zeng, W. X. Fan, Q. Li, H. Gao, H. [25] L. C. Cui, Z. Q. Zhang, X. Lu, B. Xiao, Y. Fu, RSC Adv., 2016, 6,
Wang, Adv. Synth. Catal., 2018, 360, 1032–1037. 51932–51935.
[3] Q. Liu, B. Tian, P. Tian, X. Tong, G. Q. Lin, Chin. J. Org. Chem., 2015, [26] L. Mao, K. J. Szabó, T. B. Marder, Org. Lett., 2017, 19, 1204–1207.
35, 1–14. [27] Z. C. Cao, F. X. Luo, W. J. Shi, Z. J. Shi, Org. Chem. Front., 2015, 2,
[4] Y. Qin, W. Xu, C. Hu, S. Liu, Q. Zhao, Chin. J. Inorg. Chem., 2017, 33, 1505–1510.
1705–1721. [28] S. H. Cho, J. F. Hartwig, J. Am. Chem. Soc., 2013, 135, 8157–8160.
[5] J. Yang, Z. Li, S. Zhu, Chin. J. Org. Chem., 2017, 37, 2481–2497. [29] M. A. Larsen, C. V. Wilson, J. F. Hartwig, J. Am. Chem. Soc., 2015,
[6] Z. Yang, T. Cao, Y. Han, W. Lin, Q. Liu, Y. Tang, Y. Zhai, M. Jia, W. 137, 8633–8643.
Zhang, T. Zhu, S. Ma, Chin. J. Chem., 2017, 35, 1251–1262. [30] W. N. Palmer, J. V. Obligacion, I. Pappas, P. J. Chirik, J. Am. Chem.
[7] Y. Yasu, T. Koike, M. Akita, Adv. Synth. Catal., 2012, 354, Soc., 2016, 138, 766–769.
3414–3420. [31] A. J. MacNair, C. R. P. Millet, G. S. Nichol, A. Ironmonger, S. P.
[8] F. Lima, M. A. Kabeshov, D. N. Tran, C. Battilocchio, J. Sedelmeier, G. Thomas, ACS Catal., 2016, 6, 7217–7221.
Sedelmeier, B. Schenkel, S. V. Ley, Angew. Chem. Int. Ed., 2016, 55, [32] J. V. Obligacion, P. J. Chirik, Org. Lett., 2013, 15, 2680–2683.

 
Graphical Abstract
Chin. J. Catal., 2018, 39: 1725–1729 doi: 10.1016/S1872‐2067(18)63139‐0
Cu‐catalyzed deoxygenative gem‐hydroborylation of aromatic
aldehydes and ketones to access benzylboronic esters
Lu Wang, Wei Sun, Chao Liu *
Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences;
University of Chinese Academy of Sciences
A novel copper‐catalyzed deoxygenative gem‐hydroborylation of aro‐
matic aldehydes and ketones has been developed. This direct and opera‐
tionally simple protocol provides an effective approach for the synthesis
of a variety of primary and secondary benzylboronates, in which broad
functional group tolerance was presented. Widely available B2pin2 was
used as the boron source and alcoholic proton was applied as the hy‐
dride source.
 Lu Wang et al. / Chinese Journal of Catalysis 39 (2018) 1725–1729 1729

[33] M. L. Scheuermann, E. J. Johnson, P. J. Chirik, Org. Lett., 2015, 17, Organometallics, 2015, 34, 3902–3908.
2716–2719. [43] S. P. Cummings, T. N. Le, G. E. Fernandez, L. G. Quiambao, B. J.
[34] X. Chen, Z. Cheng, Z. Lu, Org. Lett., 2017, 19, 969–971. Stokes, J. Am. Chem. Soc., 2016, 138, 6107–6110.
[35] D. Noh, H. Chea, J. Ju, J. Yun, Angew. Chem. Int. Ed., 2009, 48, [44] W. Ding, Q. Song, Org. Chem. Front., 2016, 3, 14–18.
6062–6064. [45] H. Lu, Z. Geng, J. Li, D. Zou, Y. Wu, Y. Wu, Org. Lett., 2016, 18,
[36] J. Peng, J. H. Docherty, A. P. Dominey, S. P. Thomas, Chem. Com‐ 2774–2776.
mun., 2017, 53, 4726–4729. [46] D. P. Ojha, K. Gadde, K. R. Prabhu, Org. Lett., 2016, 18, 5062–5065.
[37] J. Huang, W. Yan, C. Tan, W. Wu, H. Jiang, Chem. Commun., 2018, [47] Q. Xuan, Q. Song, Org. Lett., 2016, 18, 4250–4253.
54, 1770–1773. [48] W. Kong, Q. Wang, J. Zhu, Angew. Chem. Int. Ed., 2017, 56,
[38] H. Li, L. Wang, Y. Zhang, J. Wang, Angew. Chem. Int. Ed., 2012, 51, 3987–3991.
2943–2946. [49] Q. Xuan, C. Zhao, Q. Song, Org. Biomol. Chem., 2017, 15,
[39] D. Shi, L. Wang, C. Xia, C. Liu, Angew. Chem. Int. Ed., 2018, 57, 5140–5144.
10318–10322. [50] M. L. McIntosh, C. M. Moore, T. B. Clark, Org. Lett., 2010, 12,
[40] L. Wang, T. Zhang, W. Sun, Z. He, C. Xia, Y. Lan, C. Liu, J. Am. Chem. 1996–1999.
Soc., 2017, 139, 5257–5264. [51] H. Zhao, M. Tong, H. Wang, S. Xu, Org. Biomol. Chem., 2017, 15,
[41] A. G. Campaña, R. E. Estévez, N. Fuentes, R. Robles, J. M. Cuerva, E. 3418–3422.
Buñuel, D. Cárdenas, J. E. Oltra, Org. Lett., 2007, 9, 2195–2198. [52] D. S. Laitar, E. Y. Tsui, J. P. Sadighi, J. Am. Chem. Soc., 2006, 128,
[42] T. Bolaño, M. A. Esteruelas, M. P. Gay, E. Oñate, I. M. Pastor, M. Yus, 11036–11037.

铜催化芳香醛和酮的氢硼化转化合成苄基硼酸酯类化合物
王 露a, 孙 威a,b, 刘 超a,*
a
中国科学院兰州化学物理研究所苏州研究院, 羰基合成与选择氧化国家重点实验室, 甘肃兰州 730000
b
中国科学院大学, 北京 100049

摘要: 有机硼化合物广泛应用于合成化学、药物化学以及材料化学等领域, 开发新颖实用的方法合成有机硼化合物是重要

的研究领域. 在各种有机硼化合物中, 苄基硼酸酯有着一些特有的性质, 例如活性相对较高, 可以有效地当作苄基化试剂
使用. 目前已有多种合成苄基硼酸酯的方法, 主要集中在苄基格氏试剂或者锂试剂的硼化反应, 但是该方法底物兼容性较
差, 而且苄基格氏试剂或者锂试剂的制备比较困难. 随着催化反应的发展, 过渡金属(如Pd, Cu, Ni, Fe)催化苄基卤代物的硼
化反应及芳基卤代物和1,1-二硼类化合物的偶联反应能够有效地合成这类化合物. 一级苄醇在钯或铜的催化作用下也可
以转化为苄基硼酸酯. 苄基C–H键的催化硼化是潜在的构建苄基硼酸酯的高原子经济性的方法, 但目前其选择性和反应活
性仍不高. 在无金属催化的条件下, 对甲苯磺酰腙类化合物与HBpin或B2pin2发生1,2-金属迁移是合成苄基硼酸酯的有效方
法. 到目前为止, 虽然有很多种合成苄基硼酸酯的方法, 但仍无法满足其合成需求, 因此开发新型的方法合成苄基硼酸酯
具有重要的意义.
本文开发了一种新型的铜催化芳香醛/酮类化合物的脱氧氢硼化转化体系. 使用廉价易得的铜作为催化剂, 叔丁醇钠
或者叔丁醇钾作为碱, 醇质子作为氢源, 在100 oC的条件下, 芳香醛和芳香酮可直接转化成一级和二级苄基硼酸酯类化合
物, 该反应操作简单, 反应体系可以兼容多种官能团, 分离产率在21%–77%之间. 反应机理方面, 该转化有两种可能的过
程, (1) 反应体系中首先生成1,1-偕二硼化合物, 该化合物在碱和EtOH的作用下发生脱硼质子解, 最终转化成苄基单硼化合
物; (2) 醇质子转化成负氢物种, 并与体系中的-OBpin硼酸酯生成四配位硼, 发生1,2-迁移后得到目标产物.
为了验证上述两种反应途径的可行性, 我们进行了一系列的控制试验. 首先合成了苯乙酮的1,1-二硼化合物, 在催化
量碱与当量醇的作用下, 以99%的收率得到了脱硼质子解的产物, 说明1,1-二硼化合物可以在反应体系中转化成苄基单硼
化合物. 以苯甲醛作为原料合成了-OBpin硼酸酯, 首先将其投入到甲醇、叔丁醇钠和B2pin2的体系中, 最终得到了47%的
苄基单硼; 同时将-OBpin硼酸酯投入到HBpin与叔丁醇钠的体系中, 得到了57%的苄基单硼化合物, 说明第二种反应过程
通过1,2-迁移得到目标产物也是可行的. 在当前的实验条件下, 两种反应路径都是可能的.
关键词: 均相催化; 铜催化; 脱氧氢硼化; 芳香醛; 芳香酮

收稿日期: 2018-06-13. 接受日期: 2018-07-15. 出版日期: 2018-11-05.

*通讯联系人. 电子信箱: chaoliu@licp.cas.cn
基金来源: 国家自然科学基金(91745110, 21673261, 21603245, 21633013, 21703265); 中科院兰州化物所“特聘人才”计划; 中科院
青年促进会(2018458); 中国化学会青年人才托举工程项目; 中科院“西部之光”人才项目.
本文的电子版全文由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).