Nickel-mediated regio- and chemoselective carboxylation of alkynes in the presence of carbon dioxide

Article abstract of DOI:10.1021/jo982443f

Alkynes are carboxylated in a highly regio- and chemoselective manner in the presence of Ni(cod)₂, DBU, and CO₂ to give the carboxylated products in good yields. The reaction was carried out under very mild conditions (CO₂ 1 atm, 0°C) in the presence of a stoichiometric amount of alkynes, conjugated enynes, or diynes. The high selectivity observed in the reaction would be explained in terms of the stability and the reactivity of the intermediates.

Full text of DOI:10.1021/jo982443f

J . Org. Chem. 1999, 64, 3975-3978
3975
Nick el-Med ia ted Regio- a n d Ch em oselective Ca r boxyla tion of
Alk yn es in th e P r esen ce of Ca r bon Dioxid e
Shinichi Saito,*,† Satomi Nakagawa,‡ Toru Koizumi,‡,§ Kyoko Hirayama,| and
Yoshinori Yamamoto*,|
Institute for Chemical Reaction Science, Tohoku University, Sendai 980-8578, J apan,
Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, 2630 Sugitani,
Toyama 930-0194, J apan, and Department of Chemistry, Graduate School of Science, Tohoku University,
Sendai 980-8578, J apan
Received December 14, 1998
Alkynes are carboxylated in a highly regio- and chemoselective manner in the presence of Ni-
(cod)2, DBU, and CO2 to give the carboxylated products in good yields. The reaction was carried
out under very mild conditions (CO2 1 atm, 0 °C) in the presence of a stoichiometric amount of
alkynes, conjugated enynes, or diynes. The high selectivity observed in the reaction would be
explained in terms of the stability and the reactivity of the intermediates.
Ta ble 1. Ni(0)-Med ia ted Ca r boxyla tion of Ter m in a l
Alk yn es
Only a limited number of synthetic reactions in which
carbon dioxide is used as a C1 source is available to
organic chemists, although carbon monoxide is frequently
used. Considering the strong demand for the efficient
utilization of CO2, it is desirable to develop a CO2-
accommodating synthetic reaction.1 Some transition-
metal complexes mediate or catalyze the reactions of
unsaturated hydrocarbons with carbon dioxide, and they
are potentially useful for organic synthesis. For example,
Hoberg et al. reported that Ni(0) complexes mediate the
reaction of alkenes and alkynes with carbon dioxide (eq
1).2 However, in many cases an excess of symmetric
entry
alkyne
R
isolated yield of 2 (%)
1
2
3
4
5
6
1a
1b
1c
1d
1e
1f
Ph
85
86
91
72
58
74a
4-MeOPh
4-CF3Ph
t-Bu
TMS
n-Hex
alkyne was required to carry out the reaction efficiently,
and the reactivity of unsymmmetric alkynes or conju-
gated alkynes was scarcely investigated. Electrochemical
carboxylation of alkynes in the presence of Ni complexes
was developed by Dun˜ach et al.,3 and as a result of the
low regioselectivity, synthetic usefulness of the reaction
is currently limited. In this paper, we report highly
chemo- and regioselective carboxylation of alkynes, enynes,
and diynes in the presence of a Ni(0) complex.
a
The product was isolated as a mixture of isomers (ratio 2:3 )
16:1).
Resu lts
We found that terminal alkynes were regioselectively
carboxylated in the presence of a Ni(0) complex. A
terminal alkyne (1.1 equiv) was added slowly to a mixture
of Ni(cod)2 and DBU (2 equiv) in THF under CO2 (1 atm),
and the resulting red mixture was kept stirring for 2 h.
Aqueous hydrochloric acid was added to the mixture to
give an alkenoic acid in good yield. It is essential to use
DBU (or DBN) as the ligand; the reaction did not take
place in the presence of other ligands such as TMEDA,
DABCO, imidazole, DMAP, 2,2′-bipyridyl, or phosphine
ligands. As shown in Table 1, the reaction proceeded in
a highly regio- and stereoselective manner, and an
E-acrylic acid (2) was isolated as the sole product in most
reactions. These results are in sharp contrast to those
obtained by Dun˜ach et al.,3 in which the regioisomeric
† Institute for Chemical Reaction Science, Tohoku University.
‡ Toyama Medical and Pharmaceutical University.
§ Deceased J anuary 12, 1998.
|| Department of Chemistry, Graduate School of Science, Tohoku
University.
(1) Reviews: Aresta, M.; Quaranta, E.; Tommasi, I. New. J . Chem.
1994, 18, 133-142. Organic and Bio-organic Chemistry of Carbon
Dioxide; Inoue, S., Yamazaki, N., Eds.; Kodansha: Tokyo, 1981.
(2) (a) Burkhart, G.; Hoberg, H. Angew. Chem., Int. Ed. Engl. 1982,
21, 76. (b) Hoberg, H.; Schaefer, D.; Burkhart, G. J . Organomet. Chem.
1982, 228, C21-C24. (c) Hoberg, H.; Schaefer, D.; Burkhart, G. J .
Organomet. Chem. 1983, 255, C15-C17. (d) Hoberg, H.; Schaefer, D.;
Kru¨ger, C.; Romao, M. J . J . Organomet. Chem. 1984, 266, 203-224.
(e) Hoberg, H.; Schaefer, D.; Oster, B. W. J . Organomet. Chem. 1984,
266, 313-320. (f) Hoberg, H.; Peres, Y.; Milchereit, A. J . Organomet.
Chem. 1986, 307, C38-C40. (g) Hoberg, H.; Schaefer, D.; Kru¨ger, C.;
Tsay, Y.-H. Angew. Chem., Int. Ed. Engl. 1987, 26, 771-773. (h)
Hoberg, H.; Peres, Y.; Milchereit, A.; Gross, S. J . Organomet. Chem.
1988, 345, C17-C19. (i) Hoberg, H.; Ba¨rhausen, D. J . Organomet.
Chem. 1989, 307, C7-C11. (j) Hoberg, H.; Ballesteros, A.; Sigan, A.;
J egat, C.; Milchereit, A. Synthesis 1991, 395-398.
(3) (a) Dun˜ach, E.; Pe´richon, J . J . Organomet. Chem. 1988, 352,
239-246. (b) Dun˜ach, E.; De´rien, S.; Pe´richon, J . J . Organomet. Chem.
1989, 364, C33-C36. (c) Dun˜ach, E.; Pe´richon, J . J . Organomet. Chem.
1990, 385, C43-C46. (d) De`rien, S.; Dun˜ach, E.; Pe´richon, J . J . Am.
Chem. Soc. 1991, 113, 8447-8454. (e) De`rien, S.; Clinet, J .-C.; Dun˜ach,
E.; Pe´richon, J . Tetrahedron 1992, 48, 5235-5248.
10.1021/jo982443f CCC: $18.00 © 1999 American Chemical Society
Published on Web 05/08/1999

3976 J . Org. Chem., Vol. 64, No. 11, 1999
Saito et al.
Ta ble 2. Ni(0)-Med ia ted Ca r boxyla tion of Con ju ga ted
En yn es
enolic acid 3 was obtained as the major product. The
yields of the carboxylated products obtained by the
reaction of aromatic acetylenes were higher compared to
those of aliphatic acrylic acids (Table 1, entries 1-3 vs
entries 4-6). The yield of the product became lower in
the presence of a trimethylsilyl group (entry 5). The
regioselectivity of the reaction was slightly reduced when
a primary alkyl group was attached to the ethynyl group
(entry 6).
entry
enyne
R1, R2
isolated yield of 5 (%)
We confirmed that the rate of the reaction is affected
by the electron density of the ethynyl group. Phenyl-
acrylic acid (2a ) was the major product when a mixture
of ethynylbenzene 1a (1 equiv) and 4-methoxy-1-ethy-
nylbenzene 1b (1 equiv) was carboxylated in the presence
of Ni(cod)2 (1 equiv) and DBU (2 equiv) (eq 2).
1
2
3
4
4a
4b
4c
4d
R1 ) n-Hex, R2 ) H
R1, R2 ) -(CH2)3-
R1, R2 ) -(CH2)4-
R1, R2 ) -(CH2)5-
68
65
86
71
Ta ble 3. Ni(0)-Med ia ted Ca r boxyla tion of Diyn es
Indirect evidence for the formation of a nickelacycle
in this reaction was obtained by using a deuterated acid
as the acid for quenching the reaction mixture in the
carboxylation of 1a . The product (2a -d ) contained a
deuterium at the vinyl position (96% atom % D), which
indicates the existence of a Ni-C bond before quenching
the reaction mixture (eq 3).
reactive triple bond and another π-system seems to be a
key factor to achieve the observed high selectivity.
We further investigated the carboxylation of diynes.
Symmetric diynes 6a ,b reacted with CO2 (1 atm) in the
presence of the Ni(0) complex to give substituted 1-ene-
3-ynoic acids 7a ,b in good yields (Table 3). The reaction
of unsymmetric diynes 6c,d proceeded smoothly, and the
carboxylated products 7c,d were obtained as sole prod-
ucts. It is interesting to note that the position of the
carboxylation is strictly controlled, and the C-C bond
was formed at the “terminal” carbon atom (i.e., 1- or
4-position) of the diyne. It is also possible to control the
chemoselectivity by the introduction of a bulky substitu-
ent. Thus, 1,3-octadiyne 6c reacted to give a linear acid
7c, whereas 1-triphenylsilyl-1,3-octadiyne 6d reacted to
give a branched acid 7d (Table 3, entries 3-4).
To investigate the effect of the conjugation of the
ethynyl group on the regioselectivity, we next chose
conjugated enynes as substrates of the reaction.
3-Methyene-1-nonyne 4a was carboxylated in a highly
chemo- and regioselective manner to give the correspond-
ing dienoic acid 5a in good yield (Table 2, entry 1). The
other enynes 4b-d also reacted smoothly to yield the
carboxylated products. It is noteworthy that, in all cases,
Discu ssion
The most interesting features of the carboxylation
reaction we report are the high regioselectivity and the
importance of the ligand (DBU). These features will be
closely related to the mechanistic rationale of this reac-
tion, which we will discuss in the following section.
1
no isomeric products were detected by H NMR spectra
of the reaction mixtures. The conjugation between the

Ni-Mediated Carboxylation of Alkynes in CO2
J . Org. Chem., Vol. 64, No. 11, 1999 3977
It is well-known that nickel forms a complex with
alkenes and alkynes, and complex 8 will be the initial
intermediate of this reaction.4 Considering the result of
the experiment using deuterated acid for workup and the
results obtained by Hoberg et al.,2 it is reasonable to
postulate a nickelacycle 9 as the important intermediate
in the next step. The mechanistic rationale of this
reaction will then become quite similar to that proposed
by Dun˜ach et al.,3 though the regioselectivity is com-
pletely different.
be reduced under Dun˜ach’s condition to give an acid 3.
The carboxylic acid was not isolated under our condition
as a result of the unfavorable equilibrium.
It may be possible to explain the result of the competi-
tive experiment in terms of the existence of the equilib-
rium between 1 and 8. There would be a stronger
interaction between the electron-deficient alkyne and the
Ni(0) since it has been shown that the electron-deficient
alkynes react with the Ni(0) to give a more stable
alkyne-Ni(0) complex.5 Therefore, a larger amount of
phenylacetylene-Ni(0) complex would be formed in the
reaction mixture. The complex will irreversibly react with
CO2, and the carboxylated product (phenylacrylic acid)
would be isolated as the major product.
A significant difference between our reaction condition
and that of Dun˜ach is the choice of the ligand, and it
would be possible to interpret the results in terms of the
difference of the ligands bound to the Ni atom (eq 4).
Con clu sion
We found that alkynes are carboxylated in a highly
regio- and chemoselective manner in the presence of Ni-
(cod)2, DBU, and CO2 to give the carboxylated products
in good yields. We extended the scope of this reaction and
found that conjugated enynes and diynes could be used
as the substrates. The reaction was carried out under
very mild conditions (CO2 1 atm, 0 °C) in the presence of
a stoichiometric amount of alkynes, conjugated enynes,
or diynes. The high selectivity observed in the reaction
would be explained in terms of the stability and the
reactivity of the intermediates.
Thus, the Ni-alkyne complex will be more reactive when
DBU, a highly basic ligand, is attached, and the complex
will react rapidly and irreversibly with the electrophile
(CO2) to give a nickelacycle 9. The formation of the
intermediate 9 would be kinetically favored compared to
the formation of 10 because of the steric or electronic
effect; CO2 will attack the less sterically congested carbon
atom or the carbon atom with a larger HOMO (i.e., the
“terminal” position of enyne or diyne).
When 2,2′-bipyridyl was used as the ligand, the reac-
tion did not take place under our condition. We assume
that the stability of the nickelacycle is very low, and an
equilibrium between the Ni-alkyne complex and the
nickelacycle would exist (eq 5). This equilibrium would
Exp er im en ta l Section
All melting points are uncorrected. All solvents and reagents
were purified by standard methods. Dry THF (Kanto Chemi-
cals, J apan), CO2 (Nihon Sanso, J apan), and Ni(cod)2 (Strem)
were used as purchased.
P r ep a r a tion of Alk yn es, En yn es, a n d Diyn es. Com-
pounds 1a , 1d -f, 4c, and 6a are commercially available.
4-Methoxyphenylacetylene (1b) was prepared from anisalde-
hyde by the procedure reported by Corey et al.6 4-(Trifluoro-
methyl)phenylacetylene (1c)7 was prepared by the Pd-cata-
lyzed coupling of 4-(trifluoromethyl)bromobenzene with tri-
methylsilylacetylene, followed by the removal of the trimeth-
ylsilyl group.8,9 The preparations of 4a ,10 4b,11 4d ,11 6b,12 6c,13
and 6d 14 were based on the reported procedures.
1-Tr ip h en ylsilyl-1,3-octa d iyn e (6d ): 65% yield, colorless
plates, mp 95-97 °C (recrystallized from CH2Cl2-hexane); IR
(KBr) 3067, 3024, 2955, 2936, 2219, 2109, 1428, 1182, 1113,
779, 740, 710, 698, 558, 512 cm-1; 1H NMR (500 MHz, CDCl3)
δ 0.93 (t, J ) 7.4 Hz, 3H), 1.46 (sextet, J ) 7.5 Hz, 2H), 1.54
(quint, J ) 7.5 Hz, 2H), 2.33 (t, J ) 7.1 Hz, 2H), 7.39 (t, J )
7.1 Hz, 6H), 7.44 (tt, J ) 7.3, 1.5 Hz, 3H), 7.65 (tt, J ) 6.7, 1.3
Hz, 6H); 13C NMR (125 MHz, CDCl3) δ 13.5, 19.0, 21.9, 30.0,
65.7, 77.6, 81.6, 92.7, 128.0, 130.0, 132.9, 135.6. Anal. Calcd
for C26H24Si: C, 85.66; H, 6.64. Found: C, 85.64; H, 6.92.
(5) Rosenthal, U.; Schulz, W. J . Organomet. Chem. 1987, 311, 103-
117.
(6) Corey, E. J .; Fuchs, P. L. Tetrahedron Lett. 1972, 36, 3769-3772.
(7) Kodaira, K.; Okuhara, K. Bull. Chem. Soc. J pn. 1988, 61, 1625-
1631.
(8) Brandsma, L. Preparative Acetylenic Chemistry, 2nd ed.; Elsevi-
er: Amsterdam, 1988; p 219.
(9) Matsumoto, Y.; Naito, M.; Hayashi, T. Organometallics 1992,
11, 2732-2734.
tend toward the formation of the Ni-alkyne complex. In
this case, the thermodynamically favored nickelacycle 12
would be formed as the major intermediate, which would
(10) Klusener, P. A. A.; Kulik, W.; Brandsma, L. J . Org. Chem. 1987,
52, 5261-5266.
(11) Reference 6, pp 203-204. Carlson, R. G.; Cox, W. W. J . Org.
Chem. 1977, 42, 2382-2386.
(12) Reference 6, pp 220-221. Vlassa, M.; Ciocan-Tarta, I.; Ma´r-
gineanu, F.; Oprean, I. Tetrahedron 1996, 52, 1337-1342.
(13) Reference 6, pp 51-52. Miller, J . A.; Zweifel, G. Synthesis 1983,
128-130.
(4) Chetcuti, M. J . Nickel-Carbon π-Bonded Complexes. In Com-
prehensive Organometallic Chemistry II; Abel, E. W., Stone, F. G. A.,
Wilkinson, G., Eds., Puddephatt, R. J ., Volume Ed.; Pergamon: Oxford,
1995; Vol. 9, pp 107-191.
(14) Reference 6, p 124.

3978 J . Org. Chem., Vol. 64, No. 11, 1999
Saito et al.
Gen er a l P r oced u r e for th e Ni(0)-Med ia ted Ca r boxy-
la tion of Alk yn es. To a mixture of Ni(cod)2 (550 mg, 2 mmol)
and DBU (0.6 mL, 4 mmol) in dry THF (16 mL) was added
slowly a solution of alkyne (2.2 mmol) in THF (16 mL) under
CO2 (1 atm) for 1 h at 0 °C. The dark red mixture was kept
stirring at 0 °C for 2 h. Dilute hydrochloric acid was added,
and the mixture was extracted with CH2Cl2 or AcOEt (50 mL
× 3). The combined organic layer was washed with brine, dried
over MgSO4, and evaporated. The crude product was further
purified by silica gel column chromatography (eluent, hexane/
AcOEt ) 1:1, 2:1, or 3: 1). The spectral data of 2a -c were
identical with those of authentic samples. The spectral data
of 2d 15 and 2e16 were identical with the reported data. In case
of the reaction which was quenched with a deuterated acid,
the reaction was carried out in 1 mmol scale. A 5 g portion of
deuterium chloride in D2O (20%, 99.5 atom % D, Aldrich) was
added, and the reaction mixture was kept stirring for 30 min
and extracted (yield 62%). The content of deuterium was
examined by observing the 1H NMR spectrum.
(E)-3-(1-Cycloh ep ten -1-yl)-2-p r op en oic a cid (5d ): color-
less powder, mp 118-123 °C (molecular distillation, 55 °C/0.1
mmHg); IR (KBr) 2500-3300 (br), 2923, 1678, 1608, 1442,
1410, 1311, 1276, 1210, 1179, 985, 942, 844, 696, 624, 538
cm-1; 1H NMR (270 MHz, CDCl3) δ 1.48-1.56 (m, 4H), 1.73-
1.81 (m, 2H), 2.26-2.34 (m, 4H), 5.78 (d, J ) 15.6 Hz, 1H),
6.34 (d, J ) 6.8 Hz, 1H), 7.34 (d, J ) 15.6 Hz, 1H); 13C NMR
(75 MHz, CDCl3) δ 25.8, 26.1, 27.1, 29.2, 31.8, 113.7, 142.0,
145.3, 151.5, 173.2. Anal. Calcd for C10H14O2: C, 72.26; H, 8.49.
Found: C, 72.24; H, 8.60.
2-Meth yl-2-h exen -4-yn oic a cid (7a ):18 1H NMR (270 MHz,
CDCl3) δ 2.01 (s, 3H), 2.07 (d, J ) 2.4 Hz, 3H), 6.68-6.70 (m,
1H).
2-Hexyl-2-u n d ecen -4-yn oic a cid (7b): colorless powder,
mp 38 °C (molecular distillation, 115 °C/0.15 mmHg); IR (KBr)
2500-3500 (br), 2926, 2208, 1680, 1603, 1466, 1422, 1272,
1250, 920, 890, 760 cm-1; 1H NMR (270 MHz, CDCl3) δ 0.84-
0.90 (m, 6H), 1.25-1.60 (m, 16H), 2.38-2.48 (m, 4H), 6.34 (t,
J ) 2.4 Hz, 1H); 13C NMR (68 MHz, CDCl3) δ 14.0, 12.1, 20.0,
22.5, 22.6, 28.4, 28.5, 28.7, 29.0, 29.1, 31.3, 31.6, 105.0, 122.9,
141.6, 172.8. Anal. Calcd for C17H28O2: C, 77.22; H, 10.67.
Found: C, 77.05; H, 10.81.
(2E)-4-Hexyl-2,4-p en ta d ien oic a cid (5a ): colorless plates,
mp 63-65 °C (recrystallized from CH2Cl2-hexane); IR (KBr)
2800-3300 (br), 2932, 1686, 1619, 1464, 1420, 1310, 1279,
1258, 1209, 983, 945, 868, 706 cm-1 1H NMR (270 MHz,
;
2-Non en -4-yn oic a cid (7c): yellow powder, mp 35-44 °C
(molecular distillation, 60 °C/0.15 mmHg); IR (KBr) 2500-
3400 (br), 2213, 1681, 1620, 1466, 1412, 1290, 1205, 1166, 962,
927, 862, 674, 541 cm-1; 1H NMR (270 MHz, CDCl3) δ 0.90 (d,
J ) 7.3 Hz, 3H), 1.34-1.58 (m, 4H), 2.35-2.41 (dt, J ) 7.1,
2.4 Hz, 2H), 6.12 (d, J ) 15.9 Hz, 1H), 6.82 (dt, J ) 15.6, 2.4
Hz, 1H); 13C NMR (68 MHz, CDCl3) δ 13.5, 19.5, 21.9, 30.3,
102.9, 128.3, 128.8, 171.4. Anal. Calcd for C9H12O2: C, 71.03;
H, 7.95. Found: C, 71.00; H, 8.13.
CDCl3) δ 0.87 (t, J ) 6.7 Hz, 3H), 1.27-1.50 (m, 8H), 2.22 (d,
J ) 7.6 Hz, 2H), 5.38 (d, J ) 10.4 Hz, 2H), 5.90 (d, J ) 15.9
Hz, 1H), 7.38 (d, J ) 15.9 Hz, 1H); 13C NMR (68 MHz, CDCl3)
δ 14.1, 22.6, 27.9, 29.1, 31.5, 31.6, 117.1, 124.4, 144.8, 149.2,
172.5. Anal. Calcd for C11H18O2: C, 72.49; H, 9.95. Found: C,
72.44; H, 10.29.
(E)-3-(1-Cyclop en ten -1-yl)-2-p r op en oic a cid (5b): color-
less powder, mp 146-150 °C; IR (KBr) 2500-3300 (br), 2964,
2906, 2595, 1673, 1621, 1601, 1412, 1310, 1278, 1203, 1034,
981, 959, 868, 545 cm-1 1H NMR (300 MHz, CDCl3) δ 1.99
;
2-[1-(Tr ip h en ylsilyl)-2-p r op yn e-3-yl]octa n oic a cid (7d ):
colorless powder, mp 114-122 °C (recrystallized form hexane);
IR (KBr) 2200-3300 (br), 2955, 1689, 1603, 1485, 1274, 1115,
(quint, J ) 7.5 Hz, 2H), 2.47 (m, 4H), 5.74 (d, J ) 15.6 Hz,
1H), 6.24 (s, 1H), 7.60 (d, J ) 15.6 Hz, 1H); 13C NMR (75 MHz,
CDCl3) δ 23.0, 30.7, 33.6, 117.3, 141.4, 142.1, 143.2, 173.0.
Anal. Calcd for C8H10O2: C, 69.55; H, 7.30. Found: C, 69.37;
H, 7.14.
738, 712, 699, 513, 477 cm-1 1H NMR (500 MHz, CDCl3) δ
;
0.87 (t, J ) 7.3 Hz, 3H), 1.34 (sextet, J ) 7.4 Hz, 2H), 1.51
(quint, J ) 7.7 Hz, 2H), 2.60 (t, J ) 7.8 Hz, 2H), 6.84 (s, 1H),
7.40 (t, J ) 7.5 Hz, 6H), 7.46 (t, J ) 7.4 Hz, 3H), 7.66 (d, J )
7.3 Hz, 6H); 13C NMR (126 MHz, CDCl3) δ 13.9, 22.7, 29.6,
31.0, 103.4, 104.9, 130.0, 128.1, 130.1, 132.8, 135.5, 145.2,
170.7. Anal. Calcd for C27H26O2Si: C, 78.98; H, 6.38. Found:
C, 79.14; H, 6.62.
(E)-3-(1-Cycloh exen -1-yl)-2-p r op en oic a cid (5c):17 1H
NMR (270 MHz, CDCl3) δ 1.56-1.73 (m, 4H), 2.12-2.21 (m,
4H), 5.74 (d, J ) 15.6 Hz, 1H), 6.21 (t, J ) 4.0 Hz, 1H), 7.35
(d, J ) 15.6 Hz, 1H); 13C NMR (68 MHz, CDCl3) 21.9, 22.0,
24.0, 26.5, 113.6, 134.9, 140.3, 150.4, 172.8.
J O982443F
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