ACS Catalysis
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Borylation of Bromoaryl Triflates with Diborons: Chemoselective
a possibility that boronic acids serve as an active species in the
present SMC. See SI for details.
(17) Wuts, P. G. M.; Greene, T. W. Greene’s Protective Groups in
Organic Synthesis, 4th ed.; John Wiley & Sons, Inc.; Hoboken, 2007;
p 994.
Replacement of an Ar–Br Bond. Chem. Lett. 2018, 47, 957–959. (g)
Yoshida, H.; Murashige, Y.; Osaka, I. Copper-Catalyzed B(dan)-
Installing Allylic Borylation of Allylic Phosphates. Adv. Synth. Catal.
2019, 361, 2286–2290.
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(8) (a) Tsuchimoto, T.; Utsugi, H.; Sugiura, T.; Horio, S.
(18) For another efficient SMC with 2-pyridylboranes, see:
Billingsley, K. L.; Buchwald, S. L. A General and Efficient Method
for the Suzuki–Miyaura Coupling of 2-Pyridyl Nucleophiles. Angew.
Chem. Int. Ed. 2008, 47, 4695–4698.
(19) (a) Pietsch, S.; Neeve, E. C.; Apperley, D. C.; Bertermann, R.;
Mo, F.; Qiu, D.; Cheung, M. S.; Dang, L.; Wang, J.; Radius, U.; Lin,
Z.; Kleeberg, C.; Marder, T. B. Synthesis, Structure, and Reactivity of
Anionic sp2–sp3 Diboron Compounds: Readily Accessible Boryl
Nucleophiles. Chem. Eur. J. 2015, 21, 7082–7099. (b) Molloy, J. J.;
Clohessy, T. A.; Irving, C.; Anderson, N. A.; Lloyd-Jones, G. C.;
Watson, A. J. B. Chemoselective Oxidation of Aryl Organoboron
Systems Enabled by Boronic Acid-Selective Phase Transfer. Chem.
Sci. 2017, 8, 1551–1559.
(20) The treatment with t-BuOLi or KOH might produce the
deprotonated species, whose predicted chemical shift would be
similar to that of 1a. But in any event, the borate (4) formation would
be the key to the smooth SMC.
(21) Rzepa, H. S.; Arkhipenko, S.; Wan, E.; Sabatini, M. T.;
Karaluka, V.; Whiting, A.; Sheppard, T. D. An Accessible Method for
DFT Calculation of 11B NMR Shifts of Organoboron Compounds. J.
Org. Chem. 2018, 83, 8020–8025.
(22) A transmetalation pathway via the reaction of a PdII–Ot-Bu
complex with a neutral C(sp2)–B(dan) may also be possible. See:
Carrow, B. P.; Hartwig, J. F. Distinguishing Between Pathways for
Transmetalation in Suzuki–Miyaura Reactions. J. Am. Chem. Soc.
2011, 133, 2116–2119.
(23) We have confirmed that an N,N’-dimethylated Ph–B(dan)
derivative [Ph–B(mdan)] underwent the direct SMC under the same
reaction conditions, which may support the borate-formation pathway
(not deprotonation pathway). This result, however, should be
inconclusive, since the smooth reaction also took place even with a
weak base (K3PO4), possibly indicating that the B(mdan) moiety is
sufficiently Lewis acidic to be activated. See SI for details.
(24) t-BuOH in the upper 1H NMR spectrum of Figure 5 is thought
to be generated from protonation of excess t-BuOK with adventitious
water during the preparation of an NMR sample.
(25) The reaction with Ba(OH)2 also turned out to proceed directly,
where HOB(dan) and (dan)BOB(dan) were formed as the sole boron
by-products without the release of danH2. See SI for detailed
assignment of the B(dan)-containing by-products.
(26) Tanji, Y.; Mitsutake, N.; Fujihara, T.; Tsuji, Y. Steric Effect
of Carboxylate Ligands on Pd-Catalyzed Intramolecular C(sp2)–H and
C(sp3)–H Arylation Reactions. Angew. Chem. Int. Ed. 2018, 57,
10314–10317.
Alkynylboranes:
A
Practical Approach by Zinc-Catalyzed
Dehydrogenative Coupling of Terminal Alkynes with 1,8-
Naphthalenediaminatoborane. Adv. Synth. Catal. 2015, 357, 77–82.
(b) Tani, T.; Sawatsugawa, Y.; Sano, Y.; Hirataka, Y.; Takahashi, N.;
Hashimoto, S.; Sugiura, T.; Tsuchimoto, T. Alkynyl–B(dan)s in
Various Palladium-Catalyzed Carbon–Carbon Bond-Forming
Reactions Leading to Internal Alkynes, 1,4-Enynes, Ynones, and
Multiply Substituted Alkenes. Adv. Synth. Catal. 2019, 361, 1815–
1834.
(9) For a Pd-catalyzed borylative substitution, see: Xu, L.; Li, P.
Direct Introduction of a Naphthalene-1,8-diamino boryl [B(dan)]
Group by a Pd-Catalysed Selective Boryl Transfer Reaction. Chem.
Commun. 2015, 51, 5656–5659. Although 6-methoxy-2-pyridyl–
B(dan) could be synthesized by this method, the reaction of 2-
bromopyridine and 2-bromo-6-methylpyridine turned out to be totally
unsuccessful. See SI for details.
(10) Similar stabilizing effect has been observed with B(MIDA)
and B(aam). For B(MIDA), see: ref. 4b and c. For B(aam), see: (a)
Kamio, S.; Kageyuki, I.; Osaka, I.; Hatano, S.; Abe, M.; Yoshida, H.
Anthranilamide (aam)-Substituted Diboron: Palladium-Catalyzed
Selective B(aam) Transfer. Chem. Commun. 2018, 54, 9290–9293. (b)
Kamio, S.; Kageyuki, I.; Osaka, I.; Yoshida, H. Anthranilamide
(aam)-Substituted Arylboranes in Direct Carbon–Carbon Bond-
Forming Reactions. Chem. Commun. 2019, 55, 2624–2627.
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(11) Cox, P. A.; Leach, A. G.; Campbell, A. D.; Lloyd-Jones, G. C.
Protodeboronation of Heteroaromatic, Vinyl, and Cyclopropyl
Boronic
Acids:
pH–Rate
Profiles,
Autocatalysis,
and
Disproportionation. J. Am. Chem. Soc. 2016, 138, 9145–9157.
(12) Yoshida, H. Borylation of Alkynes under Base/Coinage Metal
Catalysis: Some Recent Developments. ACS Catal. 2016, 6, 1799–
1811.
(13) Ph–B(dan) was reported to be much more resistant to aqueous
deprotection than its –B(MIDA), –B(aam) and –B(pin) counterparts,
which should be attributable to lack of its boron-Lewis acidity. See
ref. 5a.
(14) A part of this work was presented at the 99th Chemical Society
of Japan Annual Meeting, Kobe, Japan, March 16-19, 2019; Suzuki–
Miyaura Cross-Coupling Reaction of dan-Substituted Organoboranes
through Direct Activation of the B(dan) Moiety (No. 2H5-03). At the
same meeting, Prof. Mutoh and co-workers reported on a closely
related reaction; Suzuki–Miyaura Cross-Coupling of Ar–B(dan) (No.
1H5-48).
(15) Actual active species are usually R–B(OH)2 generated in situ
by hydrolysis under the SMC conditions.
(16) The reaction in the presence of water under otherwise identical
conditions only gave a trace amount of 3a, which would also rule out
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