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Y.-k. Sugiyama et al.
LETTER
mL) was added a solution of CoCl2·6H2O (6.0 mg 0.025 mmol) and
dipimp (8.0 mg, 0.03 mmol) in NMP (1.0 mL). The mixture was
stirred at 50 °C. After addition of saturated aq NH4Cl, the mixture
was extracted with Et2O. The combined organic layers were washed
with brine, dried over MgSO4, filtered through a pad of Celite and
concentrated in vacuo to give a crude mixture, which was analyzed
by 1H NMR. The residue was purified by column chromatography
on silica gel to afford the substituted benzene 3ac (220 mg, 96%
yield).
may act as a bidentate-ligating agent. Based on these con-
siderations, we propose that the phthalate-ligated complex
(alkyne)–(phthalate)CoICl (ii-b) may be present in the
equilibrium with (alkyne)–(dipimp)CoICl (ii-a) by the li-
gand-exchange reaction. The complex ii-b may have a
more electron-deficient nature by coordination of weaker
Lewis base and may be much more reactive than ii-a.
Confirmation of the more detailed mechanism must await
further study.
Acknowledgement
N
We thank the Scientific Frontier Research Project of the Ministry of
Education, Culture, Sports, Science and Technology (MEXT),
Japan for financial support. We also thank the Japan Society for the
Promotion of Science (JSPS) for a grant to Y.S.
Co-Cl
N
i
(14e)
1, 2
3
N
Supporting Information for this article is available online at
R2
R2
Cl
R1
Co
o
nSupprigI
o
tnnofrmat
N
R1
N
N
R2
Co
Cl
Z
References and Notes
Z
R2
R1
R1
ii-a
(1) (a) Reppe, W.; Schweckendiek, W. J. Justus Liebigs Ann.
1948, 560, 104. (b) Chang, C. A.; Francisco, C. G.; Gadek,
T. R.; King, J. J. A.; Sternberg, E. D.; Vollhardt, K. P. C. In
Organic Synthesis Today and Tomorrow; Trost, B. M.;
Hutchinson, C. R., Eds.; Pergamon Press: Oxford, 1981, 71–
83. (c) Schore, N. E. Chem. Rev. 1988, 88, 1081. (d) Schore,
N. E. In Comprehensive Organic Synthesis; Vol. 5; Trost, B.
M.; Fleming, I.; Paquette, L. A., Eds.; Pergamon Press:
Oxford, 1991, 1129–1162. (e) Grotjahn, D. B. In
iii-a (16e)
(18e)
O
O
O
N
N
N
N
O
N
N
O
R2
R2
Cl
R1
Co
Co
O
O
O
R1
R2
Comprehensive Organometallic Chemistry II; Vol. 12; Abel,
E. W.; Stone, F. G. A.; Wilkinson, G.; Hegedus, L., Eds.;
Pergamon Press: Oxford, 1995, 741–770. (f) Lautens, M.;
Klute, W.; Tam, W. Chem. Rev. 1996, 96, 49. (g) Saito, S.;
Yamamoto, Y. Chem. Rev. 2000, 100, 2901. (h) Malacria,
M.; Aubert, C.; Renaud, J. L. In Science of Synthesis:
Houben-Weyl, Methods of Molecular Transformations; Vol.
1; Lautens, M.; Trost, B. M., Eds.; Georg Thieme Verlag:
Stuttgart, 2001, 439–530. (i) Gevorgyan, V.;
Radhakrishnan, U.; Takeda, A.; Rubina, M.; Rubin, M.;
Yamamoto, Y. J. Org. Chem. 2001, 66, 835. (j) Varela, J. A.;
Saá, C. Chem. Rev. 2003, 103, 3787. (k) Yamamoto, Y.
Curr. Org. Chem. 2005, 9, 503. (l) Kotha, S.; Brahmachary,
E.; Lahiri, K. Eur. J. Org. Chem. 2005, 4741. (m) Gandon,
V.; Aubert, C.; Malacria, M. Curr. Org. Chem. 2005, 9,
1699. (n) Gandon, V.; Aubert, C.; Malacria, M. Chem.
Commun. 2006, 2209. (o) Chopade, P. R.; Louie, J. Adv.
Synth. Catal. 2006, 348, 2307. (p) Tanaka, K. Chem. Asian
J. 2009, 4, 508. (q) Dominguez, G.; Perez-Castells, J. Chem.
Soc. Rev. 2011, 40, 3430. (r) Weding, N.; Hapke, M. Chem.
Soc. Rev. 2011, 40, 4525.
Z
Z
R2
Cl
R1
iii-b
R1
ii-b
(18e)
R3O
R3O
N
N
N
N
O
O
O
O
=
=
,
i-Pr
i-Pr
phthalate
dipimp
Scheme 6 Proposed mechanism
In summary, we found that the addition of a catalytic
amount of dicarbonyl or diol compounds can greatly acti-
vate the alkyne [2+2+2]-cycloaddition catalyst,
dipimp/CoCl2·6H2O/Zn (in NMP), to enable a high yields
of sterically demanding hexa-substituted benzenes from
unactivated simple aliphatic internal alkynes. Among ad-
ditives investigated, dimethyl phthalate was found to be
the most effective. This simple method of catalyst activa-
tion with use of inexpensive, commercially available
compounds is highly practical and may find application in
the laboratory as well as in industry.
(2) Recent examples: (a) Shibata, T.; Uchiyama, T.; Yoshinami,
Y.; Takayasu, S.; Tsuchikama, K.; Endo, K. Chem.
Commun. 2012, 48, 1311. (b) Shibata, T.; Miyoshi, M.;
Uchiyama, T.; Endo, K.; Miura, N.; Monde, K. Tetrahedron
2012, 68, 2679. (c) Brun, S.; Torrent, A.; Pla-Quintana, A.;
Roglans, A.; Fontrodona, X.; Benet-Buchholz, J.; Parella, T.
Organometallics 2012, 31, 318. (d) Ogaki, S.; Shibata, Y.;
Noguchi, K.; Tanaka, K. J. Org. Chem. 2011, 76, 1926.
(e) Weding, N.; Jackstell, R.; Jiao, H.; Spannenberg, A.;
Hapke, M. Adv. Synth. Catal. 2011, 353, 3423.
(f) Kawatsura, M.; Yamamoto, M.; Namioka, J.; Kajita, K.;
Hirakawa, T.; Itoh, T. Org. Lett. 2011, 13, 1001.
(g) Iannazzo, L.; Vollhardt, K. P. C.; Malacria, M.; Aubert,
C.; Gandon, V. Eur. J. Org. Chem. 2011, 3283. (h) Mori, F.;
Typical Procedure for the Cycloaddition of Diynes 1 and Al-
kyne 2 Catalyzed by a dipimp/CoCl2·6H2O/Zn Reagent with a
Phthalate Activator: To a mixture of dimethyl phthalate (14.6 mg,
0.075 mmol), zinc powder (3.3 mg, 0.05 mmol), 1,6-diyne 1a (174
mg, 0.5 mmol), and 4-octyne 2c (0.23 mL, 1.5 mmol) in NMP (1.0
Synlett 2012, 23, 2549–2553
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