Table 1. 2:1 Coupling of DMAD with 1-Hexyne (2a)a
Scheme 1. 2:1 Coupling of DMAD with Monoynes
1
2a
(mmol)
time
(h)
yield of 3a
yield of 4
(%)
b
b
entry
(mmol)
(%)
1
2
3
4
2
2
2
2
1
1.2
2
0.5
1
1
89
98
98
97
11
2
2
5
24
3
a
A mixture of 1, 2a, [Ir(cod)Cl]2 (0.02 mmol), dppe (0.04 mmol), and
toluene (5 mL) was stirred under refluxing toluene. b Isolated yield based
on 1.
cyclotrimerization of 1. The molar ratio of 1 to 2a affected
the yield of 3a. The results are summarized in Table 1. The
reaction using 0.6 equiv of 2a gave 3a in 98% yield (entry
2
). Cyclotrimerization of 1 was not suppressed completely.
The rich chemistry of metallacycles gives various useful
transformations in selective organic synthesis. Both late and
early transition metals can be used for this chemistry.
Product 4 was obtained in 2% yield.
On the basis of these results, we examined the scope of
the 2:1 coupling. The results are summarized in Table 2.
4
5
6
Catalytic reactions via nickelacycles, palladacycles, cobal-
7
8
9
tacycles, rhodacycles and ruthenacycles have been exten-
sively studied and used for the synthesis of cyclic compounds
from an acyclic substrate. Since Collman et al. first reported
the synthesis of an iridacyclopentadiene from the reaction
with DMAD (1) in 1968,10 the reactivity
and structure of iridacyclopentadiene have been studied.
Table 2. 2:1 Coupling of DMAD with 2a
yield 3 yield 4
of IrCl(N
2
)(PPh
)
3 2
b
b
entry
2
conditions
product
(%)
(%)
1
1
1
2
3
4
5c
6
7
8
9
2b
2c
2d
2e
2f
2g
2h
2i
toluene reflux 1 h
xylene reflux 20 h
toluene reflux 5 h
toluene reflux 5 h
THF reflux 12 h
THF reflux 0.5 h
THF reflux 20 h
dioxane reflux 20 h
THF reflux 1 h
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
96
38
86
83
91
89
52
41
90
98
93
89
73
78
2
50
3
2
0
0
16
0
0
0
However, there have been few reports on catalytic organic
synthesis via iridacyclopentadiene.12
The reaction of 1 with 1-hexyne (2a) in the presence of a
1
3,14
catalytic amount of [Ir(cod)Cl]
2
/dppe gave 3a and 4.
c
Product 3a resulted from the 2:1 coupling of two molecules
of 1 with one molecule of 2a. Product 4 resulted from
c
c
c
2j
2k
2l
(
4) (a) Saito, S.; Yamamoto, Y. Chem. ReV. 2000, 100, 2901. (b) Lautens,
M.; Klute, W.; Tam. W. Chem. ReV. 1996, 96, 49. (c) Ojima, I.;
10
THF 50 °C 2 h
THF 50 °C 1 h
Tzamarioudaki, M.; Li, Z.; Donovan, R. J. Chem. ReV. 1996, 96, 635.
1
1
1
1
2
3
0
(5) (a) Sato, Y.; Nishimata, T.; Mori, M. J. Org. Chem. 1994, 59, 6133.
d
2m THF 50 °C 1 h
2n
2o
10
11
15
(
b) Montogomery, J. Acc. Chem. Res. 2000, 33, 467. (c) Ikeda, S. Acc.
Chem. Res. 2000, 33, 511.
6) (a) Gevorgyan, V.; Radhakrishnan, U.; Takeda, A.; Rubina, M.;
d,e
d,f
THF 50 °C 2 h
THF 50 °C 3.5 h
(
14
Rubin, M.; Yamamoto, Y. J. Org. Chem. 2001, 66, 2835. (b) Trost, B. M.
Acc. Chem. Res. 1990, 23, 34.
a
A mixture of 1 (2 mmol), 2 (1.2 mmol), [Ir(cod)Cl]2 (0.02 mmol), dppe
b
(
7) (a) Vollhardt, K. P. C. Angew. Chem., Int. Ed. Engl. 1984, 23, 539.
b) Vollhardt, K. P. C. Acc. Chem. Res. 1977, 10, 1.
8) (a) Grigg, R.; Scott, R.; Stevenson, P. J. Chem. Soc., Perkin Trans.
1988, 1357. (b) McDonald, F. E.; Zhu, H. Y. H.; Holmquist, C. R. J.
(0.04 mmol), and solvent (5 mL) was stirred. Isolated yield based on 1.
c
[Ir(cod)Cl]2 (0.03 mmol), dppe (0.06 mmol). 2 (2 mmol). e Slow addition
d
(
f
(
of 1 for 0.5 h. Slow addition of 1 for 2 h.
1
Am. Chem. Soc. 1995, 117, 6605. (c) Witulski, B.; Stengel, T. Angew. Chem.,
Int. Ed. 1999, 38, 2426. (d) Wender, P. A.; Gamber, G. G.; Hubbard, R.
D.; Zhang, L. J. Am. Chem. Soc. 2002, 124, 2876. (e) Cao, P.; Wang, B.;
Zhang, X. J. Am. Chem. Soc. 2000, 122, 6490. (f) Witulski, B.; Alayrac,
C. Angew. Chem., Int. Ed. 2002, 41, 3281.
DMAD smoothly reacted with 0.6 equiv of various monoynes
(2) under mild conditions. The reaction with 1-decyne (2b)
(9) (a) Mitsudo, T.; Kondo, T. Synlett 2001, 309. (b) Yamamoto, Y.;
proceeded at room temperature to give a product in high
yield (entry 1). The reaction with phenylacetylene (2c)
Takagishi, H.; Itoh, K. J. Am. Chem. Soc. 2002, 124, 28. (c) Yamamoto,
Y.; Nakagai, Y.; Ohkoshi, N.; Itoh, K. J. Am. Chem. Soc. 2001, 123, 6372.
(
d) Trost, B. M. Chem. ReV. 2001, 101, 2067.
10) Collman, J. P.; Kang, J. W.; Little, W. F.; Sullivan, M. F. Inorg.
Chem. 1968, 7, 1298.
11) (a) O’Connor, J. M.; Closson, A.; Gantzel, P. J. Am. Chem. Soc.
002, 124, 2434. (b) O’Connor, J. M.; Closson, A.; Hiibner, K.; Merwin,
(
(13) General Procedure. A typical procedure is described (Table 1, entry
2). To a toluene solution (5 mL) of [Ir(cod)Cl]2 (13.4 mg, 0.02 mmol) and
dppe (15.9 mg, 0.04 mmol) was added 1-hexyne (0.099 g, 1.2 mmol) via
a syringe. Dimethyl acetylenedicarboxylate (0.284 g, 2 mmol) was then
added to the solution by a syringe. The reaction mixture was stirred under
reflux for 1 h. The progress of the reaction was monitored by GLC. After
dimethyl acetylenedicarboxylate was consumed, toluene was evaporated
in vacuo. Column chromatography of the residue gave 3a as a colorless oil
(n-hexane/AcOEt ) 80/20, 0.359 g, yield 98%) and 4a as a colorless oil
(n-hexane/AcOEt ) 60/40, 0.003 g, yield 2%).
(
2
R.; Gantzel, P. Organometallics 2001, 20, 3710. (c) O’Connor, J. M.;
Hiibner, K.; Closson, A.; Gantzel, P. Organometallics 2001, 20, 1482. (d)
O’Connor, J. M.; Hiibner, K.; Merwin, R.; Gantzel, P. K.; Fong, B. S.;
Adams, M.; Rheingold, A. L. J. Am. Chem. Soc. 1997, 119, 3631. (e)
O’Connor, J. M.; Hiibner, K.; Merwin, R.; Pu, L.; Rheingold, A. L. J. Am.
Chem. Soc. 1995, 117, 8861. (f) Rappoli, B. J.; Churchill, M. R.; Janik, T.
S.; Rees, W. M.; Atwood, J. D. J. Am. Chem. Soc. 1987, 109, 5145.
(14) Preparation of [Ir(cod)Cl]2, see: Crabtree, R. H.; Quirk, J. M.;
Felkin. H.; Fillebeen-Khan, T. Synth. React. Inorg. Met.-Org. Chem. 1982,
12, 407.
(12) Catalytic carbonylation via iridacyclopentadiene was reported, see:
Shibata, T.; Yamashita, K.; Ishida, H.; Takagi, K. Org. Lett. 2001, 3, 1217.
3660
Org. Lett., Vol. 5, No. 20, 2003