552
LETTER
The First Example of Polymer-supported Alkenyl Iodonium Salts: Efficient
Synthesis of b-Functional Enamines
E
a
fficient
S
i
ynthes
a
is of
b
-Fun
n
ctional
E
nam
g
ines -Min Chen,a,c Xian Huang*a,b
Department of Chemistry, Zhejiang University, Xixi Campus, Hangzhou 310028, P. R. China
b
State key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai,
200032, P. R. China
Fax +86(571)88807077; E-mail: huangx@mail.hz.zj.cn
a
Department of Chemistry, Gannan Teachers’ College, Ganzhou 341000, P. R. China
Received 24 December 2003
We began our efforts to prepare the polymer-supported
alkenyl(phenyl) iodonium salts by the treatment of
poly{[4-hydroxy(tosyoxy)iodo]styrene}(resin 1)6b with
terminal alkenes, such as styrene and a-methylsyrene, or
a,b-unsaturated ketones and esters, but no satisfactory re-
sults were got. Luckily, polymer-supported alkenyl(phe-
nyl) iodonium salts were obtained when methyl-3-amino-
crotonate (2a) and ethyl-3-benzylamino-crotonate (2b)
were used following the conditions that Papoutsis4c et al.
devised in the solution conditions (Scheme 1). The resin 1
and methyl-3-amino-crotonate (2a) or ethyl-3-benzylami-
no-crotonate (2b) were stirred at 0 °C for 6 hours. The
resulting solution was evaporated in vacuo carefully and
Et2O was added to precipitate the white polymeric alke-
nyl(phenyl) iodonium salts7 3a and 3b. The elemental
analysis of the nitrogen component is 3.09% (3a, N:
2.21mmol/g) and 2.44% (3b, N: 1.74 mmol/g) respective-
ly, which implies the polymer-supported Koser’s reagent
(resin 1) have been converted almost quantitatively to
polymer-supported alkenyl(phenyl) iodonium salts 3.
Abstract: Polymer-supported alkenyl(phenyl) iodonium salts were
synthesized, which served as effective alkenyl transfer reagents for
the preparation of b-functional enamines; the polymer support
poly(4-iodostyrene) can be regenerated and recycled.
Key words: polymer-supported alkenylphenyl iodonium salts,
poly(4-iodostyrene), b-functional enamines
Polymer-supported organic reagents have been extensive-
ly applied to the preparation of the organic molecules.1
The most important point is that the regeneration and re-
use of the recovered polymer-supported reagents are pos-
sible, thus providing an environmentally benign system.
Hypervalent iodine reagents have attracted wide attention
due to their unique chemical properties.2 Among them,
alkenyl(phenyl) iodonium salts are very important re-
agents as synthons of alkenyl cations in organic synthe-
sis.3 Most of the syntheses of alkenyl(phenyl) iodonium
salts were realized by the reaction of an activated alkene
with iodine(III) species4 or addition of nucleophiles to
alkynyl(phenyl) iodonium salts.5 However, to the best of
our knowledge, no examples of polymer-supported alke-
nyl(phenyl) iodonium salts have been reported. During
continuing our efforts to develop new polymer-supported
hypervalent iodine reagents,6 we were interested in the
synthesis of polymer-supported alkenyl iodonium salts. In
this paper, we report the first preparation of polymer-sup-
ported alkenylphenyl iodonium salts, and their application
as alkenyl transfer reagents to synthesize b-functional
enamines.
The conversion was also established by IR spectroscopy
with the shifting of the characteristic peaks of -SO2- from
1187 to 1170 cm–1 (3a) or 1171 cm–1 (3b), and the appear-
ance of peaks at 3176 and 3076 cm–1 (NH2, 3a) or
3043cm–1 (BnNH, 3b) and 1629 cm–1 (C=O, 3a), or 1625
cm–1 (C=O, 3b). The polymer-supported alkenyl(phenyl)
iodonium salts are stable in air, and no decomposition was
observed over a period of one week at room temperature,
but it is better to store the resin products away from direct
sunlight and in a refrigerator.
CH2Cl2, 0 oC
H3C
H
H3C
I
+
I (OH)OTs
OTs
R1HN
CO2R2
R1HN
CO2R2
1
3
2
2a, R1=H; R2=CH3
2b, R1=Bn; R2=C2H5
Scheme 1
SYNLETT 2004, No. 3, pp 0552–0554
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Advanced online publication: 26.01.2004
DOI: 10.1055/s-2004-815431; Art ID: U29103ST
© Georg Thieme Verlag Stuttgart · New York