Distannylation of strained carbon-carbon triple bonds catalyzed by a palladium complex

Article abstract of DOI:10.1002/anie.200460189

Oxidative addition of a distannane to a palladium(0) complex occurs during the distannylation of in situ generated arynes with distannanes in the presence of a catalytic amount of a palladium/tert-octyl isocyanide (tOcNC) complex to give 1,2-distannylarenes in moderate to high yields (see scheme). Bisarynes and cyclohexynes can also be used as substrates for the reaction.

Full text of DOI:10.1002/anie.200460189

Communications
Homogeneous Catalysis
Distannylation of Strained Carbon–Carbon Triple
Bonds Catalyzed by a Palladium Complex**
Hiroto Yoshida,* Kenji Tanino, Joji Ohshita, and
Atsutaka Kunai*
Transformations of arynes catalyzed by a transition-metal
complex, although less common than stoichiometric reac-
tions,[1] have recently received considerable attention as a
novel route for the synthesis of substituted arenes that are not
accessible by conventional methods. Irrespective of the
catalyst and reactant used, efforts have thus far been devoted
mainly to developing cyclization reactions of arynes. The
pioneering workon these transformations—palladium-cata-
lyzed trimerization of arynes[2] and cocyclization of arynes
[*] Dr. H. Yoshida, K. Tanino, Prof. J. Ohshita, Prof. A. Kunai
Department of Applied Chemistry
Graduate School of Engineering
Hiroshima University
Higashi-Hiroshima 739-8527 (Japan)
Fax: (+81)82-424-5494
E-mail: yhiroto@hiroshima-u.ac.jp
akunai@hiroshima-u.ac.jp
[**] We thank Central Glass Co Ltd. for a generous gift of trifluorome-
thanesulfonic anhydride.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
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DOI: 10.1002/anie.200460189
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with alkynes[3]—was reported by Peæa et al. Catalytic reac-
tions of arynes with alkynes and/or allyl chlorides in the
presence of a palladium complex have also been reported by
Yamamoto and co-workers,[4] while Murai and co-workers
have developed cobalt-, rhodium-, and palladium-catalyzed
carbonylative cycloadditions of arynes.[5] Catalytic addition
reactions of a s bond[6] to arynes have been limited to
carbostannylation[7a] and disilylation,[7b] as reported previ-
ously. Herein we report that a tin–tin bond of a distannane
readily adds to strained carbon–carbon unsaturated com-
pounds, such as arynes or cyclohexynes, in the presence of a
palladium complex [Eq. (1)]. This transition-metal-catalyzed
element–element s-bond addition reaction to cyclohexynes
has no precedents, to the best of our knowledge.
provide the corresponding distannylation products 3ab–3ad,
respectively, in moderate to high yields (entries 2–4), whereas
the reaction of 4-fluorobenzyne (formed from 2e) gave only a
low yield of the desired product (entry 5). The distannylation
reaction was also applied to 4,5-disubstituted benzynes
(formed from 2 f or 2g) or sterically more congested arynes
(formed from 2h–2j) to afford good to high yields of products
3af–3aj, respectively (entries 6–10). In addition to 1a,
hexamethyldistannane (1b) could also be used as the tin-
containing starting material, and in this case the less-reactive
1,2-naphthalyne (from 2k), 3-phenylbenzyne (from 2l), or
9,10-phenanthryne (from 2m) were found to insert into the
tin–tin bond (entries 11–14, respectively);[12] in most cases a
compound resulting from cyclotrimerization of the aryne
(triphenylene) was formed as a by-product. The reaction with
1b also produced a trace amount of 2,2’-distannylbiaryl as
well; for example, triphenylene and 2,2’-bis(trimethylstan-
nyl)biphenyl were obtained in 9% and 3% yields in the
reaction summarized in entry 11.
We first examined the reaction of hexabutyldistannane
(1a) and benzyne, prepared in situ from 2-(trimethylsilyl)-
phenyl triflate (2a),[8] and a fluoride ion (KF/[18]crown-6) in
the presence of a palladium/1,1,3,3-tetramethylbutyl isocya-
nide (tert-octyl isocyanide, tOcNC) complex,[9] and found that
the tin–tin bond of 1a smoothly adds to benzyne to afford 1,2-
bis(tributylstannyl)benzene (3aa) in 73% yield (entry 1,
Table 1).[10] The choice of catalyst and source of the fluoride
ion are crucial: the reaction did not proceed in the presence of
either [Pd(dba)2] (dba = trans,trans-dibenzylideneacetone) or
[Pd(PPh3)4], and the desired product was also not formed
when CsF in MeCN[11] was used as the source of the fluoride
ion, even in the presence of the same palladium–isocyanide
complex. The distannylation of various arynes was then
investigated under the optimized reaction conditions. As in
the case of benzyne itself, the 4-substituted benzynes formed
in situ from precursors 2b–2d react efficiently with 1a to
The reaction of an aryne containing two triple bonds is
noteworthy: treatment of the bisaryne precursor 2n with 1a
gave bis[3,4-bis(tributylstannyl)phenyl] ether 3an in which
four carbon–tin bonds are formed in one step [Eq. (2); Tf =
trifluoromethanesulfonyl, TMS = trimethylsilyl].
Table 1: Distannylation of arynes.
The distannylation reaction was
also found to be suitable for cyclo-
hexynes (Scheme 1). When in situ
generated cyclohexyne (formed
from 2o) was treated with 1a
under the above-mentioned reac-
Entry
Distannane
R’ in 2
Precursor
t [h]
Yield [%][a]
Product
tion conditions the insertion prod-
uct 1,2-bis(tributylstannyl)cyclo-
1
2
3
4
5
6
7
8
1a (R = Bu)
H
4-Me
4-MeO
4-Ph
4-F
4,5-Me2
4,5- -(CH2)3-
6-Me
3-MeO
3,6-(MeO)2
H
2a
2b
2c
2d
2e
2 f
2g
2h
2i
3
3
7
4
6.5
3
9
3.5
6
5
73
71
55
40
26
73
64
55
59
63
56
61
39
27
3aa
3ab
3ac
3ad
3ae
3af
3ag
3ah
3ai
hexene (3ao) was obtained in 70%
yield. Similarly, the reaction of sub-
stituted cyclohexynes (formed from
2p or 2q) with 1b also tookplace
successfully to provide the distan-
nylation products (3bp or 3bq) in
60 or 90% yield, respectively.
Since an aryl (or alkenyl) tri-
flate readily undergoes a cross-cou-
pling reaction with a distannane in
the presence of a palladium cata-
lyst,[13] the distannylation might pro-
ceed by a pathway that does not
9
10
11
12
13
14
2j
3aj
1b (R = Me)
2a
2k
2l
4
3ba
3bk
3bl
3,4- -(CH)4-
6-Ph
4.5
5.5
5
dibenzo[c,e][b]
2m
3bm
[a] Yield of isolated product based on distannane. [b] 9,10-Phenanthryne.
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Scheme 1. Distannylation of cyclohexynes: a) KF (3 equiv), [18]crown-6
(3 equiv), Pd(OAc)2 (2 mol%), tOcNC (30 mol%), THF, 208C.
involve an aryne (cyclohexyne) intermediate: cross-coupling
À
of 2 at a C OTf moiety with 1 followed by fluoride-ion-
induced silicon–tin exchange between the resulting 2-(trial-
kylstannyl)arylsilane (2-(trialkylstannyl)cyclohexenylsilane)
and R3SnOTf.[14] However, this pathway can be ruled out
since the reaction of 4-(trimethylsilyl)phenyl triflate (2r) with
1a did not give the respective distannylation product, thus
confirming the intermediacy of an aryne (cyclohexyne) in the
distannylation process [Eq. (3)].
Scheme 3. Catalytic cycles for the distannylation.
insertion of the triple bond of the aryne or cyclohexyne into
À
an Sn Pd bond of 4 to form palladium complex 5, followed by
reductive elimination, affords the product and regenerates
the catalyst. However, formation of a triphenylene and
distannylbiaryl as by-products may suggest that another
catalytic cycle is also operative. Thus, the Pd0 complex
initially undergoes oxidative cyclization with the aryne to
generate palladacycle 6,[19] which yields the product after
reaction with 1 (cycle B).[20,21] The by-products could also
arise from 6: the interaction of 6 with a second aryne instead
of 1 gives a five-membered palladacycle 7, which reacts
further with a third aryne[22] or 1[23] to afford a triphenylene or
distannylbiaryl, respectively.
We assumed that this reaction is initiated by oxidative
0
[15]
À
addition of an Sn Sn bond of a distannane to a Pd complex
and thus we examined the stoichiometric reaction shown in
Scheme 2. Thus, treatment of the Pd0–isocyanide complex[16]
In conclusion, distannylation of arynes or cyclohexynes
has been accomplished in the presence of a catalytic amount
of a palladium–tert-octyl isocyanide complex, and diverse 1,2-
distannylarenes or 1,2-distannylcyclohexenes, which could
have high synthetic utility as bis(anion) equivalents, have
been readily synthesized. Moreover, the catalytic pathway,
which includes oxidative addition of a distannane to a
palladium(0) complex, has been confirmed by the stoichio-
metric reaction. Further studies on synthetic applications to
other strained cycloalkynes and s bonds are in progress.
Scheme 2. Elucidation of the mechanism by stoichiometric reactions:
a) 2a (1.5 equiv), KF (3 equiv), [18]crown-6 (3 equiv), THF, 208C, 1 h.
with an equimolar amount of 1a led to the quantitative
formation of the oxidative-addition product 4a,[17,18] which
exhibits high reactivity for the insertion of benzyne to afford
3aa in 74% yield. These results prompted us to propose
cycle A depicted in Scheme 3. First, complex 4 is produced by
oxidative addition of 1 to the Pd0 complex. Subsequent
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[11] The combination of CsF and MeCN has been employed
Experimental Section
frequently in the catalytic transformations of arynes, see
Ref. [3–5] and [7a].
[12] No trace of the distannylation products of these arynes was
found in the reaction with 1a.
[13] a) S. A. Hitchcock, D. R. Mayhugh, G. S. Gregory, Tetrahedron
Lett. 1995, 36, 9085; b) G. Stork, R. C. A. Isaacs, J. Am. Chem.
Soc. 1990, 112, 7399.
[14] B. P. Warner, S. L. Buchwald, J. Org. Chem. 1994, 59, 5822.
[15] Oxidative addition of a distannane to a palladium(0) complex
has been proposed to be an initiation step in the distannylation
of alkynes, see Ref. [6a].
[16] a) S. Otsuka, A. Nakamura, Y. Tatsuno, J. Am. Chem. Soc. 1969,
91, 6994; b) M. Suginome, H. Oike, S.-S. Park, Y. Ito, Bull. Chem.
Soc. Jpn. 1996, 69, 289.
[17] The configuration of 4a (cis or trans) could not be elucidated.
[18] Oxidative addition of a distannane to a palladium(0)–phosphane
complex: Y. Tsuji, K. Nishiyama, S. Hori, M. Ebihara, T.
Kawamura, Organometallics 1998, 17, 507.
3aa: Compounds 1a (0.13 g, 0.22 mmol) and 2a (0.098 g, 0.33 mmol)
were added to
a solution (1.0 mL) of 1,1,3,3-tetramethylbutyl
isocyanide (9.2 mg, 0.066 mmol), Pd(OAc)2 (1.0 mg, 4.4 mmol), KF
(0.038 g, 0.66 mmol) and [18]crown-6 (0.17 g, 0.66 mmol) in THF, and
the resulting mixture was stirred at 208C for 3 h. The mixture was
then diluted with ethyl acetate, filtered through celite, and concen-
trated. Column chromatography on alumina (hexane as eluent,
activity IV) followed by gel-permeation chromatography (benzene as
eluent) gave 3aa as a colorless oil (0.11 g, 73% yield); 1H NMR
(400 MHz, CDCl3): d = 0.88 (t, J = 7.1 Hz, 18H), 1.01–1.07 (m, 12H),
1.27–1.53 (m, 24H), 7.19–7.22 (m, 2H), 7.42–7.55 ppm (m, 2H);
13C NMR (99.5 MHz, CDCl3): d = 10.9, 13.6, 27.5, 29.2, 127.1, 137.5,
151.9 ppm; 119Sn NMR (147.5 MHz, CDCl3): d = À43.2 ppm. Ele-
mental analysis calcd for C30H58Sn2: C 54.91, H 8.91; found: C 55.18, H
8.97.
Received: April 1, 2004
[19] M. Retbøll, A. J. Edwards, A. D. Rae, A. C. Willis, M. A.
Bennett, E. Wenger, J. Am. Chem. Soc. 2002, 124, 8348; see
also Ref. [1c] and [1d].
[20] The palladium-catalyzed carbostannylation of arynes has also
been reported to proceed via palladacycle 6: T. Matsubara,
Organometallics 2003, 22, 4297; see also Ref. [7a].
[21] We could not substantiate cycle B by a stoichiometric reaction
because an attempt to prepare palladacycle 6 by the reaction of
[Pd(tOcNC)2] with 2a and KF/[18]crown-6 was unsuccessful.
[22] The five-membered palladacycle 7 has been proposed to be a
key intermediate in the palladium-catalyzed trimerization of
arynes, see Ref. [2a].
[23] The reaction of a five-membered palladacycle, derived from a
Pd0 complex and 2 mol of an alkyne, with an organostannane has
been demonstrated to be a key step in the palladium-catalyzed
dimerization-carbostannylation of alkynes: a) E. Shirakawa, H.
Yoshida, Y. Nakao, T. Hiyama, J. Am. Chem. Soc. 1999, 121,
4290; b) H. Yoshida, E. Shirakawa, Y. Nakao, Y. Honda, T.
Hiyama, Bull. Chem. Soc. Jpn. 2001, 74, 637.
Keywords: arynes · cycloalkynes · homogeneous catalysis ·
palladium · tin
.
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