Palladium-iminophosphine-catalysed carbostannylation of arynes: Synthesis of ortho-substituted arylstannanes

Article abstract of DOI:10.1039/b103745p

Arynes were found to insert into a carbon-tin bond of alkynyl- and vinylstannanes in the presence of a catalytic amount of a palladium-iminophosphine complex to afford ortho-substituted arylstannanes, which were convertible into a wide variety of 1,2-disu

Full text of DOI:10.1039/b103745p

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Palladium–iminophosphine-catalysed carbostannylation of arynes:
synthesis of ortho-substituted arylstannanes†
Hiroto Yoshida,a‡ Yuki Honda,a Eiji Shirakawa*b and Tamejiro Hiyama*a
a Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Sakyo-ku,
Kyoto 606-8501, Japan. E-mail: thiyama@npc05.kuic.kyoto-u.ac.jp
b Graduate School of Materials Science, Japan Advanced Institute of Science and Technology, Asahidai,
Tatsunokuchi, Ishikawa 923-1292, Japan
Received (in Cambridge, UK) 25th April 2001, Accepted 13th August 2001
First published as an Advance Article on the web 5th September 2001
Arynes were found to insert into a carbon–tin bond of
alkynyl- and vinylstannanes in the presence of a catalytic
amount of a palladium–iminophosphine complex to afford
ortho-substituted arylstannanes, which were convertible into
a wide variety of 1,2-disubstituted arenes via carbon–carbon
bond forming reactions.
the C–Sn bond of tributyl(vinyl)tin (2h), which was unreactive
towards alkynes under similar catalytic conditions (entry
8).1a,e
The carbostannylation was also applicable to substituted
benzynes (Scheme 2). The reaction of 2a with 4-Me-substituted
benzyne precursor 3b provided regioisomeric products 4i and 5i
in a ratio of 51+49. 5-Me-Substituted benzyne precursor 3c also
gave a similar ratio of 4i and 5i in a similar yield. These results
indicate that common intermediate 4-methylbenzyne should be
involved in both reactions. Similarly, 3-methoxybenzyne (from
3d) and 1,2-naphthalyne§ (from 3e) underwent carbostannyla-
tion with 2a and afforded the corresponding products consisting
of two regioisomers in 58 and 42% yield, respectively.
Herein we report palladium–iminophosphine-catalysed carbo-
stannylation1–3 of arynes, demonstrating that the novel catalytic
process offers a convenient method to generate variously ortho-
substituted arylstannanes, which are applicable to biaryl
syntheses through the Migita–Kosugi–Stille coupling reaction.4
To the best of our knowledge, the present reaction is the first
demonstration of transition metal-catalysed carbometalation of
arynes.5,6
Table 1 Palladium-1-catalysed carbostannylation of benzynea
First we investigated the carbostannylation of in situ prepared
benzyne in the presence of a palladium(0) complex coordinated
by N-(2-diphenylphosphinobenzylidene)-2-phenylethylamine
(1) (Scheme 1 and Table 1). When 2-(trimethylsilyl)phenyl
triflate (3a) and CsF were allowed to react with tri-
Entry
Organostannane
Time/h
Yield (%)b Product
1
3
54
3
butyl(phenylethynyl)tin (2a) at 50 °C for 3 h using [Pd2Cl2(h -
C3H5)2] and 1 (5 mol% of Pd, Pd/1 = 1) in acetonitrile,
tributyl[2-(phenylethynyl)phenyl]tin (4a) was produced in 54%
yield7,8 along with diphenylacetylene as a by-product (entry 1).
Formation of diphenylacetylene can be ascribed to cross-
coupling of 3a at the C–OTf bond with 2a followed by fluoride
ion-induced protodesilylation.9 Tributyl(3,3-dimethylbut-
1-ynyl)tin (2b) also reacted smoothly with benzyne to afford 4b
in 53% yield (entry 2). Aliphatic alkynylstannanes 2c and 2d
also participate in the reaction, providing the corresponding
carbostannylation products (entries 3 and 4). Addition of
tributyl(3-methoxyprop-1-ynyl)tin (2e) to benzyne took place
effectively, indicating that a propargylic ether is compatible
with the reaction (entry 5). The reaction of conjugated
enynylstannanes 2f and 2g proceeded as well to give
2-(enynyl)phenylstannanes in 51 and 35% yield, respectively
(entries 6 and 7). Worthy of note is that benzyne inserted into
2
3
8
4
53
41
4
5
0.5
2.5
30
51
6
2
51
7
1.5
25
35
47
8c
a The reaction was carried out in MeCN (3 mL) at 50 °C using an
organostannane (0.34 mmol), 3a (0.69 mmol) and CsF (0.69 mmol) in the
Scheme 1
3
presence of [Pd2Cl2(h -C3H5)2] (8.2 mmol) and 1 (0.016 mmol). b Isolated
† Electronic supplementary information (ESI) available: experimental
details. See http://www.rsc.org/suppdata/cc/b1/b103745p/
yield based on the organostannane. c 2b–3a–CsF = 1+3+6.
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Chem. Commun., 2001, 1880–1881
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b103745p

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Scheme 4 Reagents and conditions: i, 4-NO2-C6H4-I (1.5 equiv.), CuI
(0.75 equiv.), 10 mol% of Pd(PPh3)4, DMF, 50 °C, 33 h; ii, PhCOCl
(1.5 equiv.), 2.5 mol% of Pd2 (dba)3, NMP, 30 °C, 48 h; iii, n-BuLi
(1.5 equiv.), THF, 278 °C, 1 h then PhCHO (1.5 equiv.), 278 °C-rt, 1 h.
ies on the mechanism as well as carbostannylations using other
organostannanes and unsaturated compounds are in progress in
our laboratories.
We thank the Ministry of Education, Science, Sports and
Culture, Japan, for the Grant-in-Aids for COE Research on
Elements Science, No. 12CE2005. E. S. thanks the Asahi Glass
Foundation for financial support.
Notes and references
‡ Present address: Department of Chemistry and Chemical Engineering,
Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima
739-8527, Japan.
§ The IUPAC name for 1,2-naphthalyne is 1,2-didehydronaphthalene.
¶ The IUPAC name for benzhydrol is diphenylmethanol.
1 For alkynes: (a) E. Shirakawa, H. Yoshida, T. Kurahashi, Y. Nakao and
T. Hiyama, J. Am. Chem. Soc., 1998, 120, 2975; (b) E. Shirakawa, H.
Yoshida, Y. Nakao and T. Hiyama, J. Am. Chem. Soc., 1999, 121, 4290;
(c) E. Shirakawa, K. Yamasaki, H. Yoshida and T. Hiyama, J. Am.
Chem. Soc., 1999, 121, 10221; (d) E. Shirakawa, H. Yoshida, Y. Nakao
and T. Hiyama, Org. Lett., 2000, 2, 2209; (e) H. Yoshida, E. Shirakawa,
T. Kurahashi, Y. Nakao and T. Hiyama, Organometallics, 2000, 19,
5671; (f) H. Yoshida, E. Shirakawa, Y. Nakao, Y. Honda and T.
Hiyama, Bull. Chem. Soc. Jpn., 2001, 74, 637.
2 For 1,3-dienes: E. Shirakawa, Y. Nakao, H. Yoshida and T. Hiyama, J.
Am. Chem. Soc., 2000, 122, 9030.
3 For 1,2-dienes: E. Shirakawa, Y. Nakao and T. Hiyama, Chem.
Commun., 2001, 263.
4 V. Farina, V. Krishnamurthy and W. J. Scott, Org. React., 1997, 50, 1.
5 Well polarised nucleophilic organometallics are apt to add to arynes
without catalysts, however, the resulting arylmetals often compete with
the initial reagents in the addition process, leading to oligomerisation
and/or polymerisation of arynes. For a review on the reactions of arynes
with nucleophiles, see: S. V. Kessar, in Comprehensive Organic
Synthesis, ed. B. M. Trost and I. Flemming, Pergamon Press, Oxford,
1991, vol. 4, pp. 483–515.
6 Very recently, Pd-catalysed cyclisation of arynes has been reported: (a)
E. Yoshikawa, K. V. Radhakrishnan and Y. Yamamoto, J. Am. Chem.
Soc., 2000, 122, 7280; (b) D. Peña, D. Pérez, E. Guitián and L. Castedo,
J. Org. Chem., 2000, 65, 6944.
7 The reaction of 2a with 1 equiv. of 3a gave 4a in lower yields.
8 When 3a and CsF were treated with 2a in the absence of the palladium
complex, only a trace amount of 4a ( < 10% yield) was obtained. Thus,
the catalysis of the palladium complex is apparently crucial in the
present reaction.
Scheme 2
Two plausible catalytic cycles of carbostannylation are
depicted in Scheme 3. Cycle A includes the formation of
complex 6 resulting from oxidative addition of an organo-
stannane to the Pd(0)–1 complex.1a,e Subsequent insertion of an
aryne into the C–Pd or Sn–Pd bond of 6 followed by reductive
elimination affords the product. Alternatively, the Pd(0)–1
complex first interacts with an aryne to produce palladacycle 7,
which furnishes the product through the reaction with an
organostannane (Cycle B).10,11 At present, no evidence is
available that determines the reaction pathway decisively.12
The synthetic utility of the carbostannylation products is
demonstrated by the palladium-catalysed cross-coupling of 4a
with 4-iodonitrobenzene or benzoyl chloride. As shown in
Scheme 4, biaryl 8 or 2-(phenylethynyl)benzophenone (9),
respectively, are produced. Furthermore, 2-(phenylethynyl)-
benzhydrol¶ (10) was obtained in 65% yield via transmetalation
of 4a with n-BuLi followed by treatment with benzaldehyde.
In conclusion, carbostannylation of arynes has been achieved
using the Pd–1 complex, and ortho-alkynyl- and vinyl-
substituted arylstannanes are readily prepared, which are
subsequently coupled with organic electrophiles. Further stud-
9 Trace amounts of a by-product resulting from the cross-coupling
reaction were detected in all cases.
10 For a review on transition metal–aryne complexes, see: M. A. Bennett
and E. Wenger, Chem. Ber., 1997, 130, 1029.
11 A palladacycle has been shown to be an intermediate species in the
palladium–diimine-catalysed dimerisation–carbostannylation of al-
kynes, see ref. 1b and 1f.
12 A referee suggested another catalytic cycle which did not involve an
aryne intermediate: cross-coupling of aryne precursor 3 at a C–OTf
moiety with an organostannane followed by tin–silicon exchange
between the resulting 2-R-phenyltrimethylsilane and TfOSnBu3. How-
ever, this catalytic cycle can be ruled out, because, according to this
catalytic cycle, the reaction of a substituted benzyne should afford a
single isomer in contrast to the results demonstred herein.
Scheme 3
Chem. Commun., 2001, 1880–1881
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