ORGANIC
LETTERS
2012
Vol. 14, No. 1
38–41
Synthesis of δ-Carbolines via a
Pd-Catalyzed Sequential Reaction from
2-Iodoanilines and N-Tosyl-enynamines
Jian Cao,* Yongping Xu, Yulong Kong, Yuming Cui, Ziqiang Hu, Guanhai Wang,
Yuan Deng, and Guoqiao Lai*
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of
Education, Hangzhou Normal University, Wenyi Road 222, Hangzhou 310012,
People’s Republic of China
caojianhznu@yahoo.cn; gqlai@hznu.edu.cn
Received October 15, 2011
ABSTRACT
A facile Pd-catalyzed sequential reaction has been developed for the synthesis of δ-carbolines from 2-iodoanilines and N-tosyl-enynamines. This
protocol involves Larock heteroannulation/elimination/electrocyclization/oxidative aromatization cascade sequences and allows access to
multisubstituted δ-carbolines in moderate to good yields.
Pyrido[x,y-b]indoles, commonly known as carbo-
lines, are not only the fundamental motif found in
various natural alkaloids but also the key structural
units for pharmaceutical compounds.1 Thus the syn-
thesis of carbolines has attracted considerable at-
tention and many methods have been established for
their synthesis, such as Pd-catalyzed intramolecular
arylation of arylaminopyridines,2 [2 þ 2 þ 2] cycload-
dition of o,N-dialkynyl-N-tosylanilides and nitriles,3
and photostimulated cyclization of anilinohalopyri-
dines.4
Compared with R-, β-, and γ-carbolines, few methods
are described for the synthesis of δ-carbolines.5 Therefore
it is important to develop direct and efficient strategies
that afford δ-carboline derivatives.
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r
10.1021/ol2027762
Published on Web 11/30/2011
2011 American Chemical Society