84.27 (2C), 25.06, 25.03; 11B NMR: δ 30.35 (br), 22.36. HRMS
(APCI-MS, positive): m/z = 482.2806. calcd for C30H37B2O4:
482.2804 [M+H]+.
References
1.
K. N. Campbell, L. T. Eby, J. Am. Chem. Soc. 1941, 63,
(Z)-1-(1-Cyclohexeyl)-2-phenyl-1,2-
216.
bis(pinacolatoboryl)ethene (2j): Synthesized via GP1. White
solid (0.21 g, 0.53 mmol, 53%, E:Z = 4:96). H NMR: δ 7.19–
2.
Reviews: a) K. N. Campbell, B. K. Campbell, Chem. Rev.
1942, 31, 77. b) D. J. Pasto, Reduction of C=C and C≡C
by Noncatalytic Chemical Methods. in Comprehensive
Organic Synthesis, ed. by B. M. Trost, I. Fleming,
Pergamon, Oxford, 1991; pp. 471–488.
a) L. I. Smith, H. H. Hoehn, J. Am. Chem. Soc. 1941, 63,
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Soc. B 1967, 418. d) D. A. Dadley, A. G. Evans, J. Chem.
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C. Xu, A. Wakamiya, S. Yamaguchi, Org. Lett. 2004, 6,
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Zhang, T. Karasawa, H. Yamada, A. Wakamiya, S.
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Neue, W. E. Piers, M. Parvez, Angew. Chem. Int. Ed. 2012,
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Wang, X. Pan, J. Wu, Inorg. Chem. 2018, 57, 12552.
M. Fukazawa, F. Takahashi, K. Nogi, T. Sasamori, H.
Yorimitsu, Org. Lett. 2020, 22, 2303.
Our recent report on borylation chemistry with alkali
metals and bis(pinacolato)diboron (B2pin2). F. Takahashi,
K. Nogi, T. Sasamori, H. Yorimitsu, Org. Lett. 2019, 21,
4739.
Reviews on 1,2-diboration reactions: a) J. Takaya, N.
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Rev. 2016, 116, 9091. c) A. B. Cuenca, R. Shishido, H. Ito,
E. Fernández, Chem. Soc. Rev. 2017, 46, 415.
Selected recent examples of 1,2-diboration of alkynes: a)
C. Kojima, K.-H. Lee, Z. Lin, M. Yamashita, J. Am. Chem.
Soc. 2016, 138, 6662. b) A. Yoshimura, Y. Takamachi, K.
Mihara, T. Saeki, S.-I. Kawaguchi, L.-B. Han, A. Nomoto,
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1
7.22 (m, 2H), 7.15–7.17 (m, 2H), 7.10–7.13 (m, 1H), 5.36–5.38
(m, 1H), 1.87–1.91 (m, 2H), 1.67–1.69 (m, 2H), 1.36–1.40 (m,
4H), 1.33 (s, 12H), 1.27 (s, 12H); 13C NMR: δ 142.50, 138.56,
128.76, 127.41, 125.87, 125.79, 83.97, 83.72, 28.49, 25.55,
24.99, 24.93, 22.95, 22.13; 11B NMR: δ 29.74 (br), 22.25. HRMS
(APCI-MS, positive): m/z = 436.2958. calcd for C26H38B2O4:
436.2960 [M]+.
(Z)-1-Phenyl-1,2-bis(pinacolatoboryl)-1-hexene (2k):
Synthesized via GP2. Purification was done by short silica gel
column and GPC according to GP1. Yellow oil (0.35 g, 0.84
mmol, 80%) was obtained from 1.05 mmol (0.17 g) of 1k. All
the resonances in the 1H, 13C, and 11B NMR spectra were
consistent with the reported values.30
3.
4.
(Z)-1-Phenyl-1,2-bis(pinacolatoboryl)propene
(2l):
Synthesized via GP2. Purification was done by short silica gel
column and GPC according to GP1. Yellow oil (0.27 g, 0.73
mmol, 72%) was obtained from 1.02 mmol (0.12 g) of 1l. All the
resonances in the 1H, 13C, and 11B NMR spectra were consistent
with the reported values.29
(Z)-1-Cyclopropyl-2-phenyl-1,2-
bis(pinacolatoboryl)ethene (2m): Synthesized via GP2. The
diboration step was conducted at –78 °C. Yellow solid (0.27 mg,
0.68 mmol, 72%). 1H NMR: δ 7.28 (t, J = 7.5 Hz, 2H), 7.21 (d,
J = 7.5 Hz, 2H), 7.16–7.18 (m, 1H), 1.56–1.60 (m, 1H), 1.35 (s,
12H), 1.23 (s, 12H), 0.77–0.74 (m, 2H), 0.57–0.60 (m, 2H); 13
C
NMR: δ 142.58, 129.29, 127.70, 125.66, 84.04, 83.76, 25.55,
24.86, 15.95, 7.81; 11B NMR: δ 29.87, 22.36. HRMS (APCI-MS,
positive): m/z = 396.2644. calcd for C23H34B2O4: 396.2646 [M]+.
(Z)-1-(3-Methoxyphenyl)-3,3-dimethyl-1,2-
5.
6.
bis(pinacolatoboryl)-1-butene (2n): Synthesized via GP2.
Purification was done by short silica gel column and GPC
(eluent: toluene) according to GP1. White solid (0.13 g, 0.30
mmol, 30%). 1H NMR: δ 7.11 (t, J = 7.8 Hz, 1H), 6.67–6.71 (m,
7.
8.
3H), 3.76 (s, 3H), 1.38 (s, 12H), 1.16 (s, 12H), 0.98 (s, 9H); 13
C
NMR: δ 158.66, 145.63, 128.18, 121.36, 113.77, 111.48, 83.90,
83.70, 55.24, 38.38, 31.82, 25.69, 24.76; 11B NMR: δ 29.95 (br),
22.32. HRMS (APCI-MS, positive): m/z = 442.3068. calcd for
C25H40B2O5: 442.3065 [M]+.
(Z)-1-Phenyl-1,2-bis(pinacolatoboryl)-2-
1
(trimethylsilyl)ethene (2p): All the resonances in the H, 13C,
and 11B NMR spectra were consistent with the reported values.31
(E)-1,2-Diphenyl-1-pinacolatoboryl-2-[4-
(trifluoromethyl)phenyl]ethene (7): All the resonances in the
1H, 13C, and 11B NMR spectra were consistent with the reported
values.32
Acknowledgement
This work was supported by JSPS KAKENHI Grant
Numbers
JP16H04109,
JP18H04254,
JP18H04409,
JP19H00895, JP18K14212, and JP20K15275 as well as JST
CREST Grant Number JPMJCR19R4. We thank KOBELCO
ECO-Solutions Co., Ltd. for providing Na dispersion. We also
thank Prof. Makoto Yamashita, Dr. Kengo Sugita (Nagoya
University), and Dr. Atsushi Kaga (Kyoto University) for
preparing and providing Li powder, and Prof. Shohei Saito and
Mr. Takuya Yamakado (Kyoto University) for measurement of
the particle size of the Li powder.
9.
Recent reports on reductive transformations with Na
dispersion as a highly reactive but easy-to-handle reducing
agent: Ref. 5 and 6 and a) J. An, D. N. Work, C. Kenyon,
D. J. Procter, J. Org. Chem. 2014, 79, 6743. b) M. Han, X.
Ma, S. Yao, Y. Ding, Z. Yan, A. Adijiang, Y. Wu, H. Li, Y.
Zhang, P. Lei, Y. Ling, J. An, J. Org. Chem. 2017, 82, 1285.
c) M. Han, Y. Ding, Y. Yan, H. Li, S. Luo, A. Adijiang, Y.
Ling, J. An, Org. Lett. 2018, 20, 3010. d) P. Lei, Y. Ding,
X. Zhang, A. Adijiang, H. Li, Y. Ling, J. An, Org. Lett.
2018, 20, 3439. e) B. Zhang, H. Li, Y. Ding, Y. Yan, J. An,
J. Org. Chem. 2018, 83, 6006. f) Y. Ding, S. Luo, A.
#Dedicated to Professor Eiichi Nakamura on the occasion of his
70th birthday.