Regio- and stereoselective decarbonylative carbostannylation of alkynes catalyzed by Pd/C

Article abstract of DOI:10.1002/anie.200504283

(Chemical Equation Presented) Out with the CO: The highly regio- and stereoselective aryl-, alkenyl-, and alkyl-stannylation of alkynes was achieved by the decarbonylative carbostannylation of propargyl 2-furoates in the presence of Pd/C. Various function

Full text of DOI:10.1002/anie.200504283

Angewandte
Chemie
À
C C Coupling
neacetone) in Bu2O[9] at 508C for 12 h gave (E)-2-phenyl-1-
(tributylstannyl)propen-3-yl acetate (3a) in 29% yield, as
estimated by 119Sn NMR spectroscopic analysis (Table 1,
entry 1). The yield increased to 44% with propargyl benzoate
DOI: 10.1002/anie.200504283
Regio- and Stereoselective Decarbonylative
Carbostannylation of Alkynes Catalyzed by
Pd/C**
Table 1: Palladium-catalyzed phenylstannylation ofpropargyl esters. [a]
Yoshiaki Nakao, Jun Satoh, Eiji Shirakawa,* and
Tamejiro Hiyama*
The carbometalation reaction of alkynes allows the simulta-
neous, stereoselective formation of both carbon–carbon and
carbon–metal bonds and provides us with a highly powerful
tool for the synthesis of novel organometallic reagents that
contain multisubstituted ethenes.[1] In particular, the palla-
dium- or nickel-catalyzed carbostannylation of alkynes
affords highly functionalized alkenylstannanes, which
undergo various chemoselective transformations, such as the
Kosugi–Migita–Stille coupling reaction.[2,3] Alkynyl, allyl, and
Entry Alkyne Pd catalyst
t [h] Yield of 3 [%][b]
1
2
3
4
5
6
7
2a
2b
2c
2d
2e
2e
2e
[Pd2(dba)3] (2.5 mol%)
[Pd2(dba)3] (2.5 mol%)
[Pd2(dba)3] (2.5 mol%)
[Pd2(dba)3] (2.5 mol%)
[Pd2(dba)3] (2.5 mol%)
[Pd2(dba)3] (0.1 mol%)
12
10
12
24
12
17
29 (3a)
44 (3b)
47 (3c)
37 (3d)
51 (3e)
66 (3e)
Pd/C (10 wt%; 0.2 mol% Pd) 42
77 (77)[c] (3e)
acylstannanes which reportedly undergo oxidative addition of
[a] The reaction was carried out in Bu2O (0.15 mL) using 1a (40 mg,
0.10 mmol) and an alkyne (0.20 mmol) in the presence ofa palladium
catalyst at 508C. [b] Estimated by 119Sn NMR spectroscopic analysis with
Bu4Sn as the internal standard. [c] Yield ofthe isolated product based on
1a.
[4]
À
a C Sn bond to palladium(0) and nickel(0) complexes, are
successfully applied to the carbostannylation reaction,
whereas aryl-, alkenyl-, and alkylstannanes are found to be
sluggish probably because of their low potential for oxidative
addition to low-valent transition-metal complexes.[5,6] Herein,
we report the first examples of aryl-, alkenyl-, and alkyl-
stannylations of alkynes through the decarbonylative addition
of acylstannanes[7] catalyzed by Pd/C [Eq. (1)].[8]
(2b; Table 1, entry 2). The introduction of an electron-
donating methoxy group at the 4-position of the phenyl ring
of 2b slightly improved the yield (Table 1, entry 3), whereas a
lower yield was observed with an electron-withdrawing
substituent (Table 1, entry 4). We thus surveyed various
propargyl arenecarboxylates with an electron-rich aromatic
group and finally found that heteroaromatic propargyl 2-
furoate (2e) was the most effective (Table 1, entry 5).
Surprisingly, use of a smaller amount (0.1 mol%) of [Pd2-
(dba)3] gave a better result (Table 1, entry 6); inexpensive and
readily separable Pd/C (0.2 mol% of Pd) was equally
effective to give phenylstannylation product 3e in 77%
yield (Table 1, entry 7), though 42 hours was needed for
completion. It is worth noting that no regio- and stereoiso-
mers were observed, no benzoylstannylation product (non-
decarbonylative addition, see below) was detected, and a
small amount (< 5% as determined by 119Sn NMR spectros-
copy) of a bis-stannylation product was observed as a by-
product in the crude reaction mixture. Nickel catalysts, such
as [Ni(cod)2] (cod = cyclooctadiene), which catalyzed non-
decarbonylative additions of acylstannanes across internal
alkynes,[2b,f] were totally ineffective.
During our investigation of the acylstannylation of
alkynes, we observed that the reaction of benzoyl-
(tributyl)stannane (1a) with propargyl acetate (2a;
2.0 equiv) using 2.5 mol% of [Pd2(dba)3] (dba = dibenzylide-
[*] Prof. Dr. E. Shirakawa
Department ofChemistry
Graduate School ofScience
Kyoto University, Kyoto 606-8502 (Japan)
Fax: (+81)75-753-3988
E-mail: shirakawa@kuchem.kyoto-u.ac.jp
Dr. Y. Nakao, J. Satoh, Prof. Dr. T. Hiyama
Department ofMaterial Chemistry
Graduate School ofEngineering
Kyoto University, Kyoto 615-8510 (Japan)
Fax: (+81)75-383-2445
We next examined the substrate scope and found that a
substituent such as a methoxy, chloro or ortho-methyl group
in aroylstannanes (1b–1e) was tolerated (Table 2, entries 1–
4), whereas 2-furoylstannane 1 f gave the corresponding
E-mail: thiyama@npc05.kuic.kyoto-u.ac.jp
[**] This work was supported financially by Grant-in-Aids for Creative
Scientific Research (No. 16GS0209) and COE Research on “Ele-
ments Science” and on a “United Approach to New Material
Science” from MEXT.
furylstannylation product in
a modest yield (Table 2,
entry 5). The reaction of 3-methyl-2-butenoylstannane (1g)
or propanoylstannane (1h) gave an alkenyl- or alkylstanny-
lation product in 73 or 42% yield, respectively (Table 2,
entries 6 and 7). Propargyl 2-furoates with a substituent such
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
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Communications
[a]
Table 2: Palladium-catalyzed decarbonylative carbostannylation ofpropargyl 2-uf roates.
decarbonylated
product,
tributyl-
(phenyl)stannane, but benzil and hexabu-
tyldistannane [Eq. (2)]. The result shows
that the decarbonylation is likely to take
place after step (2), namely, not before
insertion of an alkyne moiety.[10] Accord-
ingly, the catalytic cycle may be described as
shown in Scheme 1. Thus, after oxidative
addition to an acyl–Sn bond, regioselective
Entry
1
Acylstannane
Alkyne
t [h]
Product
Yield [%][b]
2e
38
65
À
insertion of an alkyne into the Pd Sn bond
triggered by the coordination of the ester
carbonyl group gave alkenyl palladium
complex 5.[11] Considering the high efficien-
cies of the arenecarboxylates with an elec-
tron-rich 2-furyl or 4-methoxyphenyl group
(Table 1, entries 3 and 5), the high nucleo-
philicity of the carbonyl group in the
arenecarboxylates is likely to be important
in the promotion of this insertion step.
Decarbonylation[12] from 5 followed by
reductive elimination, which may be
driven by the p-accepting character of the
carbonyl ligand[13,14] in 6, gives the decar-
bonylative carbostannylation product and
regenerates the palladium(0) complex.
2
3
2e
2e
46
37
61
58
4
5
2e
2e
40
40
82
45
The carbostannylation products are
unique reagents that possess both nucleo-
philic alkenylstannane and electrophilic
allyl carboxylate moieties. The synthetic
versatility of the tin reagents is demon-
strated in Scheme 2. Reaction of 3e with
methyl 2-(bromomethyl)acrylate (9) under
[Pd2(dba)3] catalysis proceeded selectively
at the alkenylstannane moiety to give 10,
whereas treatment of 3e with sodium mal-
onate in the presence of a Pd/PPh3 catalyst
transformed the furoate moiety to give 11
exclusively in 74% yield. These transforma-
tions were performed sequentially with
bifunctional substrate 12 to afford cyclized
product 14 via 13.
6
7
8
2e
2e
48
40
38
73
42
35
1a
1a
9
40
42
65
46
10
1a
[a] Unless otherwise noted, the reaction was carried out in Bu2O (0.15 mL) with an acylstannane
(0.10 mmol) and an alkyne (0.20 mmol) in the presence ofPd/C (10 wt%, 0.2 mg; 0.2 mol% Pd) at
508C. [b] Yield ofthe isolated product based on the acylstannane.
In summary, we have demonstrated the
decarbonylative addition of acylstannanes
as a methyl, phenyl or ethynyl group at the propargyl position
(2d–2 f) also underwent the reaction with 1a (Table 2,
entries 8–10). On the other hand, the reaction of 1a with
homopropargyl 2-furoate was sluggish (< 20% yield), and
other alkynes, such as N-propargylsuccinimide, homopro-
pargyl phenyl ether, ethyl propiolate, 2-butyn-4-yl 2-furoate
and 1-octyne, were completely inert to the present reaction.
In view of the proposed mechanism of the previously
reported palladium- or nickel-catalyzed carbostannylations of
alkynes,[2] it is reasonable to consider that the catalytic cycle
of the present reaction should consist of 1) oxidative addition
across propargyl 2-furoates to achieve the first aryl-, alkenyl-,
and alkylstannylation reactions of alkynes. Both of the thus-
obtained alkenylstannane and allyl furoate functionalities in
the products have been shown to undergo the Kosugi–Migita–
Stille cross-coupling and the Tsuji–Trost allylation, respec-
tively. Our current efforts are directed to the expansion of the
scope and elucidation of the detailed mechanism of the
present chemistry.
À
of a C Sn bond, 2) insertion of an alkyne, and 3) reductive
elimination to give the decarbonylative carbostannylation
product with decarbonylation after step (1) or (2). Treatment
of 1a with [Pd2(dba)3] in the absence of an alkyne gave no
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10221 – 10222; c) E. Shirakawa, H. Yoshida, Y. Nakao, T.
Hiyama, Org. Lett. 2000, 2, 2209 – 2211; d) H. Yoshida, E.
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2000, 19, 5671 – 5678; e) R. Hua, S. Onozawa, M. Tanaka,
Organometallics 2000, 19, 3269 – 3271; f) E. Shirakawa, Y.
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Commun. 2001, 1926 – 1927; g) B. Martín-Matute, E. Buæuel,
M. MØndez, C. Nieto-Oberhuber, D. J. Cµrdenas, A. M. Echa-
varren, J. Organomet. Chem. 2003, 687, 410 – 419; h) E. Shir-
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Hiyama, Angew. Chem. 2004, 116, 3530 – 3533; Angew. Chem.
Int. Ed. 2004, 43, 3448 – 3451; for accounts, see: i) E. Shirakawa,
T. Hiyama, Bull. Chem. Soc. Jpn. 2002, 75, 1435 – 1450; j) E.
Shirakawa, T. Hiyama, J. Organomet. Chem. 2002, 653, 114 – 121.
[3] The allylstannylation of alkynes through the nucleophilic
addition of allylstannanes across alkynes activated by a Lewis
acid is known, see: a) N. Asao, Y. Matsukawa, Y. Yamamoto,
Chem. Commun. 1996, 1513 – 1514; b) Y. Matsukawa, N. Asao,
H. Kitahara, Y. Yamamoto, Tetrahedron 1999, 55, 3779 –
3790; for the radical-mediated allylstannylation of
alkynes, see: c) K. Miura, D. Itoh, T. Honda, H. Saito,
H. Ito, A. Hosomi, Tetrahedron Lett. 1996, 37, 8539 –
8542.
Scheme 1. A plausible catalytic cycle; see text for details.
[4] For alkynylstannanes, see: a) B. Cetinkaya, M. F. Lap-
pert, J. McMeeking, D. E. Palmer, J. Chem. Soc., Dalton
Trans. 1973, 1202 – 1208; b) E. Shirakawa, H. Yoshida, T.
Hiyama, Tetrahedron Lett. 1997, 38, 5177 – 5180; c) M.
Herberhold, U. Steffl, W. Milius, B. Wrackmeyer, Chem.
Eur. J. 1998, 4, 1027 – 1032; d) T. Matsubara, K. Hirao,
Organometallics 2002, 21, 4482 – 4489; for allyl and
acylstannanes, see references [2g] and [2e], respectively.
[5] Many reports on the oxidative addition of organostan-
nanes to platinum(0) complexes are available, see: a) C.
Eaborn, A. Pidcock, B. R. Steele, J. Chem. Soc., Dalton
Trans. 1976, 767 – 776; b) G. Butler, C. Eaborn, A.
Pidcock, J. Organomet. Chem. 1978, 144, C23 – C25;
c) G. Butler, C. Eaborn, A. Pidcock, J. Organomet.
Chem. 1979, 181, 47 – 59; d) C. Eaborn, K. Kundu, A.
Pidcock, J. Chem. Soc., Dalton Trans. 1981, 1223 – 1332.
[6] The palladium-catalyzed arylstannylation of norbornene
using aryl(trichloro)stannanes has been proposed to
proceed through the oxidative addition of an Ar–Sn
bond to palladium(0) complexes, see: a) K. Fugami, Y. Mishiba,
S. Hagiwara, D. Koyama, M. Kameyama, M. Kosugi, Synlett
2000, 553 – 555; aryl- and alkenylstannanes undergo the palla-
dium-catalyzed dimerization/carbostannylation of alkynes not
through oxidative addition but through the reaction with
palladacyclopentadienes; see: b) H. Yoshida, E. Shirakawa, Y.
Nakao, Y. Honda, T. Hiyama, Bull. Chem. Soc. Jpn. 2001, 74,
637 – 647.
Scheme 2. Transformations of phenylstannylation product 3e. a) [Pd2(dba)3]
(5 mol%), N-methylpyrrolidone, 508C, 2–3 h; b) [{PdCl(h3C3H5)}2] (2.5 mol%),
PPh3 (10 mol%), THF, room temperature, 3.5 h.
Experimental Section
General procedure for the decarbonylative carbostannylation of
propargyl esters: Pd/C (10 wt%, 0.2 mg) was added to a solution of an
acylstannane (0.10 mmol) and a propargyl ester (0.20 mmol) in
dibutyl ether (0.15 mL), and the resulting reaction mixture was
stirred at 508C for the time specified in Tables 1 and 2. The reaction
mixture was filtered through a Florisil pad, concentrated in vacuo,
and purified by flash chromatography (hexane/ethyl acetate) on silica
gel to give carbostannylation products.
Received: December 2, 2005
Published online: March 3, 2006
[7] Acyl(tributyl)stannanes are readily prepared by the reaction of
aldehydes with tributylstannylmagnesium or -lithium reagents,
see: a) M. Kosugi, H. Naka, T. Sano, T. Migita, Bull. Chem. Soc.
Jpn. 1987, 60, 3462 – 3464; b) J. A. Marshall, A. W. Garofalo,
K. W. Hinke, Org. Synth. 1999, 77, 98 – 106.
[8] For decarbonylative 1,4-carbosilylation of 1,3-dienes through
three-component coupling, see: a) Y. Obora, Y. Tsuji, T.
Kawamura, J. Am. Chem. Soc. 1995, 117, 9814 – 9821; b) Y.
Obora, Y. Tsuji, T. Kawamura, J. Am. Chem. Soc. 1993, 115,
10414 – 10415.
À
Keywords: C C coupling · metalation · palladium · tin
.
[1] a) J. F. Normant, A. Alexakis, Synthesis 1981, 841 – 870; b) P.
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[9] The use of other ethereal solvents, such as THF, 1,4-dioxane, 1,2-
dimethoxyethane (DME), toluene, and dimethyl formamide
(DMF), gave inferior results.
[10] In contrast, benzoyl(trimethyl)stannane is readily decarbony-
lated to give trimethyl(phenyl)stannane upon treatment with a
catalytic amount of [Ni(cod)2] in the absence of an unsaturated
[2] a) E. Shirakawa, H. Yoshida, T. Kurahashi, Y. Nakao, T. Hiyama,
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Communications
compound, see: E. Shirakawa, Y. Nakao, H. Yoshida, T. Hiyama,
J. Am. Chem. Soc. 2000, 122, 9030 – 9031.
À
[11] A similar regioselective insertion of propargyl pivalate into a H
Pt bond has been proposed, see: G. Stork, M. E. Jung, E. Colvin,
Y. Noel, J. Am. Chem. Soc. 1974, 96, 3684 – 3686.
[12] Acyl–palladium intermediates are reluctant to undergo decar-
bonylation ( ꢀ 2008C), as observed in the palladium-catalyzed
decarbonylation of acyl halides or aldehydes, whereas the
presence of an alkene and/or a base accelerates decarbonylation
in the decarbonylative coupling reaction of acid chlorides with
alkenes; see reference [8] and a) J. O. Hawthorne, M. H. Wilt, J.
Org. Chem. 1960, 25, 2215 – 2216; b) J. Tsuji, K. Ohno, J. Am.
Chem. Soc. 1968, 90, 94 – 98; c) J. W. Verbicky, Jr., B. A.
Dellacoletta, L. Williams, Tetrahedron Lett. 1982, 23, 371 – 372;
d) H.-U. Blaser, A. Spencer, J. Organomet. Chem. 1982, 233,
267 – 274.
[13] No side products, such as a hydrostannylation product derived
from b-hydride elimination, were observed during the reaction
of tributyl(propanoyl)stannane (Table 2, entry 7), thus implying
rapid reductive elimination from 6; for CO-induced reductive
elimination, see: T. Yamamoto, J. Ishizu, T. Kohara, S. Komiya,
A. Yamamoto, J. Am. Chem. Soc. 1980, 102, 3758 – 3764.
[14] The reaction under identical conditions to entry 4 in Table 2 but
under a CO atmosphere (1 atm) gave adduct 3i in less than 20%
yield, and no trace amounts of a non-decarbonylative adduct,
such as 8, was observed.
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