ORGANIC
LETTERS
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Vol. XX, No. XX
A Novel Tandem Sequence to Pyrrole
Syntheses by 5-endo-dig Cyclization of
000–000
1
,3-Enynes with Amines
Ganesan Bharathiraja, Sekarpandi Sakthivel, Mani Sengoden, and Tharmalingam
Punniyamurthy*
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati-781039,
Assam, India
Received August 13, 2013
ABSTRACT
The synthesis of pentasubstituted pyrroles has been described using molecular iodine from 1,3-enynes and amines via a sequential tandem
aza-Michael addition, iodocyclization, and oxidative aromatization. The protocol is simple and efficient to afford the target products at ambient
conditions.
9
Substituted pyrroles are important structural motifs
1
of many natural products and pharmaceutically active
and heterocycles. The designing of enynes makes this
process attractive for the construction of the target cyclic
compounds (Scheme 1). In continuation of our studies on
2
substances. They also find widespread applications in
3
material science and supramolecular chemistry. Thus,
several classical and modern methods have been developed
(
5) For examples, see: (a) Katritzky, A. R.; Zhang, S.; Wang, M.;
Kolb, H. C.; Steel, P. C. C. Heterocycl. Chem. 2002, 39, 759. (b)
Washizuka, K.-I.; Minakata, S.; Ryu, I.; Komatsu, M. Tetrahedron
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Chem. 2002, 67, 9439.
(6) For examples of transition-metal-catalyzed syntheses, see: (a)
4À6
for the synthesis of pyrroles and their derivatives.
However, the strategies for the synthesis of pentasubsti-
tuted pyrroles from the readily available substrates are
1
7
8
somewhat limited because of lack of selectivity. More
recently, electrophilic iodocyclization of alkynes has been
found to be a powerful tool for the synthesis of carbocycles
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(
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(
1
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0.1021/ol402305b r XXXX American Chemical Society