Platinum-catalysed diborylation of arynes: Synthesis and reaction of 1,2-diborylarenes

Article abstract of DOI:10.1039/b919407j

Arynes are found to be facilely inserted into bis(pinacolato)diboron by using a platinum-isocyanide catalyst, affording diverse 1,2-diborylarenes, which can be converted into o-terphenyls via Suzuki-Miyaura coupling reaction.

Full text of DOI:10.1039/b919407j

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Platinum-catalysed diborylation of arynes: synthesis and reaction
of 1,2-diborylarenesw
Hiroto Yoshida,* Kengo Okada, Shota Kawashima, Kenji Tanino and Joji Ohshita
Received (in Cambridge, UK) 17th September 2009, Accepted 25th November 2009
First published as an Advance Article on the web 13th January 2010
DOI: 10.1039/b919407j
Arynes are found to be facilely inserted into bis(pinacolato)-
diboron by using a platinum–isocyanide catalyst, affording diverse
1,2-diborylarenes, which can be converted into o-terphenyls via
Suzuki–Miyaura coupling reaction.
Table 1 Catalyst screening for diborylationa
Arylboron compounds are invaluable reagents in synthetic
organic chemistry1 for constructing diverse functional
molecules via Suzuki–Miyaura coupling,2 Petasis reaction,3
etc. While a variety of arylboron compounds can be prepared
by a reaction of aryl Grignard reagents (or aryllithiums) with
boron electrophiles and transition metal-catalysed borylation
of Ar–X (X = halogen or OTf)4 or Ar–H bonds (Scheme 1),5
the development of new synthetic approaches is still of great
importance.6
Entry
1
M
Ligand
Time/h
23
Yield (%)b
77
Pt(dba)2
2
3
Pt(dba)2
Pt(dba)2
48
22
76
61
We have already disclosed that the strained carbon–carbon
triple bond of arynes could smoothly be inserted into metal-
containing s-bonds (C–Sn,7 Sn–Sn8 or Si–Si9) in the presence
of a palladium catalyst, giving various arylstannanes and
arylsilanes in a straightforward manner. In view of the con-
trollable properties of arynes toward the insertion reaction
with the aid of transition metal catalysis,10 we envisaged that a
new method for synthesizing arylboron compounds would be
feasible depending upon the catalytic insertion reaction of
arynes into a boron-containing s-bond.11 We report herein
that a platinum–isocyanide complex efficaciously catalyses an
insertion reaction of arynes into the B–B bond of bis(pinacolato)-
diboron [(pin)B–B(pin)] to produce 1,2-diborylarenes, which
are difficult to access using conventional methods (eqn (1)).12
4
5
6
7
Pt(dba)2
Pt(dba)2
Pt(dba)2
Pt(PPh3)4
CyNC
Ph3CNC
None
22
99
16
16
10
10
0
None
0
8
Pd(OAc)2
23
0
a
The reaction was carried out in DME at 80 1C using 1a
(0.060 mmol), (pin)B–B(pin) (0.084 mmol), KF (0.12 mmol),
18-crown-6 (0.12 mmol), M (3.0 mmol) and ligand (0.015 mmol).
b
Isolated yield based on 1a.
The diborylation was found to facilely proceed in DME
at 80 1C when in situ-generated benzyne (from 1a13 and
KF/18-crown-6) was treated with (pin)B–B(pin) in the presence
of Pt(dba)2 and 1-adamantyl isocyanide (1-AdNC), giving
1,2-diborylbenzene (2a) in 77% yield (Table 1, entry 1).
Isocyanides bearing another tert-alkyl substituent also
promoted the diborylation (entries 2 and 3), whereas the
reaction using cyclohexyl or trityl isocyanide became sluggish
(entries 4 and 5). The combination of Pt(dba)2 and an iso-
cyanide ligand has proven to be vital for the diborylation, and
thus, other platinum complexes (Pt(PPh3)4 or Pt(dba)2: a
catalyst for diborylation of alkynes14 or alkenes15) and a
palladium–isocyanide complex (a catalyst for disilylation9
and distannylation8 of arynes) did not afford the desired
product at all (entries 6–8).16
ð1Þ
By using the optimized catalyst (Pt(dba)2–1-AdNC),
4-substituted arynes (from 1b–1e) and 3-methylbenzyne (from
1f) could also participate in the diborylation to provide
the respective diborylarenes (2b–2f) in high yields (Table 2,
entries 1–5). The use of disubstituted arynes further elevated
the versatility of the reaction. Thus, 3,4-dimethoxy- and
4,5-dimethyl-1,2-diborylbenzene (2g and 2h) were readily
available from the corresponding arynes in 67% and 80%
yield (entries 6 and 7), and moreover, 3,6-dimethoxybenzyne
Scheme 1 Representative methods for preparing arylboron compounds.
Department of Applied Chemistry, Graduate School of Engineering,
Hiroshima University, Higashi-Hiroshima 739-8527, Japan.
E-mail: yhiroto@hiroshima-u.ac.jp; Fax: +81-82-424-5494;
Tel: +81-82-424-7724
w Electronic supplementary information (ESI) available: Experimental
procedures including spectroscopic and analytical data. See DOI:
10.1039/b919407j
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Table 2 Platinum-catalysed diborylation of arynesa
Table
3
Synthesis of symmetrical ortho-terphenyls via Suzuki–
Miyaura couplinga
Entry
R
Time/h
Yield (%)b
2
Entry
Ar1–X
Time/h
Yield (%)b
3
1
2
3
4
5
6
7c
8
9
4-MeO (1b)
4-Me (1c)
4-F (1d)
4-Ph (1e)
6-Me (1f)
3,4-(MeO)2 (1g)
4,5-Me2 (1h)
3,6-(MeO)2 (1i)
3,6-Me2 (1j)
43
49
16
14
30
47
21
45
41
78
73
73
67
84
67
80
50
44
2b
2c
2d
2e
2f
2g
2h
2i
1
2
3
4
5
6
7
8
Ph–I
29
36
46
74
52
39
19
39
85
82
72
64
64
55
74
74
3a
3b
3c
3d
3e
3f
4-AcC6H4–I
4-O2NC6H4–I
4-NCC6H4–I
4-MeC6H4–I
4-MeOC6H4–I
3-Thienyl–Br
1-Naphthyl–I
3g
3h
2j
a
a
The reaction was carried out in DME at 80 1C using 1 (0.060 mmol),
(pin)B–B(pin) (0.084 mmol), KF (0.12 mmol), 18-crown-6 (0.12 mmol),
The reaction was carried out in DME at 80 1C using 2a
(0.039 mmol), an aryl halide (0.086 mmol), Cs2CO3 (0.090 mmol),
b
Pt(dba)2 (3.0 mol) and 1-AdNC (0.015 mmol). Isolated yield based
c
on 1. KF = 0.24 mmol, 18-crown-6 = 0.24 mmol.
b
H2O (15 mL) and Pd[P(t-Bu)3]2 (2.0 mmol). Isolated yield based on 2a.
hindrance also underwent coupling with high efficiencies
(entries 7–9).21
(from 1i) and 3,6-dimethylbenzyne (from 1j) underwent the
diborylation as well, despite steric congestion around the triple
bond (entries 8 and 9).
Successive addition of aryl halides allowed the entire coupling
process to be performed in one batch, where unsymmetrical
ortho-terphenyl 4j was obtainable in 43% yield without
isolation of the intermediary monoborylbiaryl (Scheme 3).
Various monoborylbiaryls (5a–5c) could also be synthesized
by a 1 : 1 coupling reaction of 2a with aryl iodides (Scheme 4).
In conclusion, we have demonstrated that the diborylation
of arynes smoothly proceeded by employing a platinum–
isocyanide catalyst, and that the Suzuki–Miyaura coupling
reaction of the resulting 1,2-diborylarenes gave a convenient
approach for the synthesis of ortho-terphenyls of structural
We next examined Suzuki–Miyaura coupling of the resulting
diborylarenes with aryl halides in order to demonstrate their
synthetic utility, and found that variously substituted ortho-
terphenyls could be prepared in a straightforward manner.17,18
As depicted in Table 3, treatment of 2a with iodobenzene
(2.2 eq.) using Pd[P(t-Bu)3]2 as catalyst and Cs2CO3 furnished
the doubly coupled product 3a in 85% yield (entry 1). Aryl
iodides bearing Ac, NO2, CN, Me or OMe at the para position
were smoothly coupled with 2a regardless of their electronic
properties, giving symmetrical ortho-terphenyls 3b–3f in good
yields (entries 2–6), and 3-thienyl and 1-naphthyl moieties
could also be introduced via the coupling (entries 7 and 8).
Under similar reaction conditions, a 1 : 1 coupling reaction of
2a with 1,8-dihalonaphthalenes proceeded efficiently to provide
fluoranthene derivatives (3i and 3j) in one step (Scheme 2).19,20
Furthermore, the coupling reaction using diborylarene 2a
was extended to the synthesis of unsymmetrical ortho-terphenyls
(Table 4). At first, 2a was transformed into the monoboryl-
biphenyl by reaction with iodobenzene (1.0 eq.) in the presence
of Pd(PPh3)4 catalyst and KOH. Subsequent coupling reaction
with electron-deficient (entries 1–3) or -rich (entries 4–6) aryl
halides took place successfully to afford 4a–4f, and in addition,
1-naphthyl, 9-phenanthryl and 9-anthryl halides of steric
Table 4 Synthesis of unsymmetrical ortho-terphenyls via stepwise
Suzuki–Miyaura couplinga
Entry
Ar2–X
Time/h
Yield (%)b
4
1
2
3
4
5
6
7
8
9
4-AcC6H4–I
22
16
18
21
21
29
19
24
4
93
86
72
85
68
87
87
81
64
4a
4b
4c
4d
4e
4f
4g
4h
4i
4-O2NC6H4–I
4-NCC6H4–I
4-MeC6H4–I
4-MeOC6H4–I
3-Thienyl–Br
1-Naphthyl–I
9-Phenanthryl–I
9-Anthryl–Br
a
The reaction was carried out in DME at 80 1C using monoboryl-
biphenyl (0.039 mmol), an aryl halide (0.043 mmol), Cs2CO3
b
(0.045 mmol), H2O (7.5 mL) and Pd[P(t-Bu)3]2 (2.0 mmol). Isolated
yield based on monoborylbiphenyl.
Scheme 2 Synthesis of fluoranthene derivatives via Suzuki–Miyaura
coupling.
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8 (a) H. Yoshida, K. Tanino, J. Ohshita and A. Kunai, Angew.
Chem., Int. Ed., 2004, 43, 5052; (b) H. Yoshida, K. Tanino,
J. Ohshita and A. Kunai, Chem. Commun., 2005, 5678.
9 (a) H. Yoshida, J. Ikadai, M. Shudo, J. Ohshita and A. Kunai,
J. Am. Chem. Soc., 2003, 125, 6638; (b) H. Yoshida, J. Ikadai,
M. Shudo, J. Ohshita and A. Kunai, Organometallics, 2005, 24,
156; (c) J. Ikadai, H. Yoshida, J. Ohshita and A. Kunai, Chem.
Lett., 2005, 34, 56.
10 For recent examples of transition metal-catalysed reactions of
arynes, see: (a) M. Jeganmohan, S. Bhuvaneswari and
C.-H. Cheng, Angew. Chem., Int. Ed., 2009, 48, 391;
(b) H. Yoshida, T. Morishita, H. Nakata and J. Ohshita, Org.
Lett., 2009, 11, 373; (c) T. Gerfaud, L. Neuville and J. Zhu, Angew.
Chem., Int. Ed., 2009, 48, 572; (d) S. A. Worlikar and R. C. Larock,
Org. Lett., 2009, 11, 2413; (e) S.-F. Pi, B.-X. Tang, J.-H. Li,
Y.-L. Liu and Y. Liang, Org. Lett., 2009, 11, 2309; (f) Z. Qiu
and Z. Xie, Angew. Chem., Int. Ed., 2009, 48, 5729.
Scheme 3 One-batch Suzuki–Miyaura coupling of 2a.
11 For reviews on catalytic insertion reactions of unsaturated
carbon–carbon bonds into an element–element s-bond, see:
(a) T. B. Marder and N. C. Norman, Top. Catal., 1998, 5, 63;
(b) I. Beletskaya and C. Moberg, Chem. Rev., 1999, 99, 3435;
(c) M. Suginome and Y. Ito, Chem. Rev., 2000, 100, 3221;
(d) I. Beletskaya and C. Moberg, Chem. Rev., 2006, 106, 2320.
12 Few reports are available on the selective synthesis of 1,2-
bis(pinacolatoboryl)arenes: (a) M. Shimizu, K. Shimono,
T. Kurahashi, S. Kiyomoto, I. Nagao and T. Hiyama, Bull. Chem.
Soc. Jpn., 2008, 81, 518; (b) M. Shimizu, I. Nagao, Y. Tomioka and
T. Hiyama, Angew. Chem., Int. Ed., 2008, 47, 8096. For synthesis
of other 1,2-diborylarenes, see; (c) K. Nozaki, M. Yoshida and
H. Takaya, Angew. Chem., Int. Ed. Engl., 1995, 33, 2452;
(d) K. Nozaki, M. Yoshida and H. Takaya, Bull. Chem. Soc.
Jpn., 1996, 69, 2043; (e) H. Noguchi, T. Shioda, C.-M. Chou and
M. Suginome, Org. Lett., 2008, 10, 377.
Scheme 4 Synthesis of borylbiaryls via Suzuki–Miyaura coupling.
diversity, which attract considerable attention due to their
pharmacological activity.22 Further studies on the catalytic
cycle of the diborylation as well as on a catalytic insertion
reaction of arynes into other s-bonds are in progress.
This work was financially supported by Kinki Invention Center
and Electric Technology Research Foundation of Chugoku.
We thank Central Glass Co. Ltd. for a generous gift of trifluoro-
methanesulfonic anhydride.
13 Y. Himeshima, T. Sonoda and H. Kobayashi, Chem. Lett., 1983,
1211.
14 (a) T. Ishiyama, N. Matsuda, N. Miyaura and A. Suzuki, J. Am.
Chem. Soc., 1993, 115, 11018; (b) T. Ishiyama, N. Matsuda,
M. Murata, F. Ozawa, A. Suzuki and N. Miyaura, Organometallics,
1996, 15, 713; (c) G. Lesley, P. Nguyen, N. J. Taylor, T. B. Marder,
A. J. Scott, W. Clegg and N. C. Norman, Organometallics, 1996, 15,
5137; (d) C. N. Iverson and M. R. Smith, III, Organometallics, 1996,
15, 5155; (e) R. Ll. Thomas, F. E. S. Souza and T. B. Marder,
J. Chem. Soc., Dalton Trans., 2001, 1650.
15 T. Ishiyama, M. Yamamoto and N. Miyaura, Chem. Commun.,
1997, 689.
16 Control experiments with substrates in the presence of 1-AdNC or
with substrates only did not give 2a at all.
Notes and references
1 (a) A. Pelter, K. Smith and H. C. Brown, Borane Reagents,
Academic Press, London, 1988; (b) Boronic Acids, ed.
D. G. Hall, Wiley-VCH, Weinheim, 2005.
2 (a) N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457;
(b) N. Miyaura, Top. Curr. Chem., 2002, 219, 11.
3 (a) N. A. Petasis, A. Goodman and I. A. Zavialov, Tetrahedron,
1997, 53, 16463; (b) T. Koolmeister, M. Sodergren and M. Scobie,
Tetrahedron Lett., 2002, 43, 5965.
4 (a) T. Ishiyama, M. Murata and N. Miyaura, J. Org. Chem., 1995,
60, 7508; (b) M. Murata, T. Oyama, S. Watanabe and Y. Masuda,
J. Org. Chem., 2000, 65, 164; (c) T. Ishiyama, K. Ishida and
17 Suzuki–Miyaura coupling of diborylalkenes, see: (a) S. D. Brown
and R. W. Armstrong, J. Am. Chem. Soc., 1996, 118, 6331;
(b) M. Shimizu, C. Nakamaki, K. Shimono, M. Schelper,
T. Kurahashi and T. Hiyama, J. Am. Chem. Soc., 2005, 127,
¨
12506; (c) H. Prokopcova, J. Ramırez, E. Fernandez and
´ ´ ´
C. O. Kappe, Tetrahedron Lett., 2008, 49, 4831.
N. Miyaura, Tetrahedron Lett., 2001, 57, 9813; (d) A. Furstner
¨
and G. Seidel, Org. Lett., 2002, 4, 541; (e) C. Kleeberg, L. Dang,
Z. Lin and T. B. Marder, Angew. Chem., Int. Ed., 2009, 48, 5350.
5 (a) H. Chen and J. F. Hartwig, Angew. Chem., Int. Ed., 1999, 38,
3391; (b) C. N. Iverson and M. R. Smith, III, J. Am. Chem. Soc.,
1999, 121, 7696; (c) J.-Y. Cho, M. K. Tse, D. Holmes,
R. E. Maleczka, Jr. and M. R. Smith, III, Science, 2002, 295,
305; (d) T. Ishiyama, J. Takagi, K. Ishida, N. Miyaura,
N. R. Anastasi and J. F. Hartwig, J. Am. Chem. Soc., 2002, 124,
390; (e) T. Ishiyama, Y. Nobuta, J. F. Hartwig and N. Miyaura,
Chem. Commun., 2003, 2924.
18 For recent reports on catalysed C–H borylation/Suzuki–Miyaura
coupling sequences, see: (a) P. Harrisson, J. Morris, P. G. Steel and
T. B. Marder, Synlett., 2009, 147; (b) P. Harrisson, J. Morris,
T. B. Marder and P. G. Steel, Org. Lett., 2009, 11, 3586.
19 The Suzuki–Miyaura coupling of vic-diborylphenanthrenes or
vic-diborylalkenes with 2,20-dibromobiaryls has recently been
disclosed, see ref. 12b.
20 For a palladium-catalysed reaction of arynes that gives benzo-
annulated structures, see: Z. Liu, X. Zhang and R. C. Larock,
J. Am. Chem. Soc., 2005, 127, 15716.
6 (a) M. W. Davies, C. N. Johnson and J. P. A. Harrity, Chem.
Commun., 1999, 2107; (b) Y. Yamamoto, K. Hattori, J. Ishii and
H. Nishiyama, Tetrahedron, 2006, 62, 4294; (c) P. M.
Delaney, D. L. Browne, H. Adams, A. Plant and J. P. A.
Harrity, Tetrahedron, 2008, 64, 866.
21 For Suzuki–Miyaura coupling of 2-borylbiaryls, see:
(a) B. Schilling and D. E. Kaufmann, Eur. J. Org. Chem., 1998,
701; (b) P. M. Delaney, J. E. Moore and J. P. A. Harrity, Chem.
Commun., 2006, 3323.
22 (a) P. Chavatte, S. Yous, C. Marot, N. Baurin and D. Lesieur,
J. Med. Chem., 2001, 44, 3223; (b) S. Chakraborty, C. Sengupta
and K. Roy, Bioorg. Med. Chem. Lett., 2004, 14, 4665.
7 H. Yoshida, Y. Honda, E. Shirakawa and T. Hiyama, Chem.
Commun., 2001, 1880.
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Chem. Commun., 2010, 46, 1763–1765 | 1765