4514
Q. Zheng, R. Hua / Tetrahedron Letters 51 (2010) 4512–4514
standard for GC analysis. After GC and GC–MS analyses of the reac-
Table 2 (continued)
tion mixture, volatiles were removed under reduced pressure, and
the residue was subjected to silica gel column chromatography
[eluted with CH2Cl2/petroleum ether (0:1–1:5)]. 3a was obtained
in 284.4 mg (0.96 mmol, 96%) as a colorless solid. The GC analysis
of the reaction mixture disclosed the formation of 3a in 99.6% GC
yield and no 1a was detectable in the reaction mixture. Data for
3a: 1H NMR (300 MHz, CDCl3) d 7.25–7.22 (m, 4H), 7.19–7.13 (m,
5H), 7.08–7.02 (m, 6H), 6.48 (s, 2H). 13C NMR (75 MHz, CDCl3) d
139.1, 135.9, 133.4, 129.1, 128.9, 128.0, 127.4, 126.3, 110.1. GC–
MS m/z (% rel. int.) 295 (M+, 100), 217 (8), 191 (41), 165 (15),
139 (19), 115 (13), 77 (28).
Pyrrole
Isolated yield (%)
N
F
Et
Et
3n
93
N
MeO
OMe
94
91
3o
Acknowledgments
Me
This work was supported by the National Natural Science Foun-
dation of China (20873073, 20972084). The authors greatly thank
Miss Maria Victoria Abrenica, from Wellesley College, for her kind
English proofreading.
N
3p
Ph
S
3q
93
N
Supplementary data
S
Ph
Supplementary data (general method, characterization data and
charts of 1H, 13C NMR for all products are concluded) associated
with this article can be found, in the online version, at doi:10.
3r
n-C6H13
N
n-C6H13
90 (72 h)
Ph
a
Reactions were carried out using 1.0 mmol of 1, 10.0 mmol of 2, and 0.1 mmol
of CuCl in a sealed tube.
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butadiyne also underwent the transformation with 1a to afford a
five-membered heterocyclic trimer 3q, indicating that the coordi-
native sulfur atom did not affect the catalytic activity of CuCl. 3q
and its analogs are members of an interesting class of organic mol-
ecules due to their interesting electrical and/or optical properties.6
Furthermore, although the reaction of 1,4-dialkyl-1,3-diynes
was sluggish under similar reaction conditions, using a prolonged
reaction time could render the desired pyrrole derivatives in satis-
factory yields. As an example, the reaction of 7,9-hexadecadiyne
with 1a at 100 °C for 24 h produced the corresponding pyrrole
derivative 3r in only 36% isolated yield, but the use of a longer
reaction time (up to 72 h) significantly increased the yield of 3r
to 90% isolated yield.
In conclusion, we have developed an efficient catalytic system
for the formation of 1,2,5-trisubstituted pyrrole derivatives by
the cycloaddition of 1,4-disubstituted 1,3-butadiynes with various
primary amines using CuCl as a catalyst. The noticeable advantages
of the present procedure include having easily available starting
materials, mild reaction conditions, an inexpensive catalyst, and
the high product yields. These qualities make the present catalytic
system practical and attractive in the synthesis of pyrrole
derivatives.
A typical experimental procedure for the reaction of 1,4-diphenyl-
1,3-butadiyne (1a) with aniline (2a) affording 1,2,5-triphenylpyrrole
(3a) (Table 1, entry 11): A mixture of 1,4-diphenyl-1, 3-butadiyne
(1a) (202.0 mg, 1.0 mmol), aniline (2a) (930.0 mg, 10.0 mmol), and
CuCl (9.9 mg, 0.1 mmol) was heated at 100 °C with stirring for 24 h
under a nitrogen atmosphere. After the reaction mixture was
cooled to room temperature, the crude reaction mixture was di-
luted with CH2Cl2 (2.0 mL) and cyclohexane (2.0 mL), and n-octa-
decane (127.0 mg, 0.5 mmol) was then added as an internal