Polyvinyl pyridine as a novel solid heterogeneous, recyclable catalyst for aza-Michael reaction

Article abstract of DOI:10.1055/s-2006-949381

Polyvinyl pyridine (PVP) is prepared by radical polymerization of 4-vinyl pyridine. PVP was used as a heterogeneous basic catalyst for the aza-Michael reaction of secondary amines and carbamates with α,β-unsaturated esters, cyanides and ketones to obtain the corresponding adducts in excellent yields (70-90%). Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-949381

2676
LETTER
Polyvinyl Pyridine as a Novel Solid Heterogeneous, Recyclable Catalyst for
aza-Michael Reaction
Recyclable
C
atalys
i
t
for az
v
a-Michael
R
e
eaction k P. Raje, Ramakrishna P. Bhat, Shriniwas D. Samant*
Organic Chemistry Research Laboratory, Department of Chemistry, Institute of Chemical Technology, University of Mumbai,
N. M. Parekh Marg, Matunga, Mumbai-400 019, India
Fax +91(22)24145614; E-mail: samantsd@yahoo.com
Received 15 January 2006
of various secondary amines as well as carbamates with
Abstract: Polyvinyl pyridine (PVP) is prepared by radical poly-
compounds containing electron-deficient double bonds.
merization of 4-vinyl pyridine. PVP was used as a heterogeneous
basic catalyst for the aza-Michael reaction of secondary amines and
carbamates with a,b-unsaturated esters, cyanides and ketones to
obtain the corresponding adducts in excellent yields (70–90%).
The PVP used in this study was soluble in methanol and
chloroform but insoluble in most other solvents. The poly-
mer was prepared in powder form by radical polymeriza-
tion of 4-vinyl pyridine.9 It was not cross-linked and its
molecular weight was found to be in the range of 2.6–
3.0·105 with a PDI of 1.5. The reaction of diethylamine
with methyl acrylate in the presence of 5% by weight of
PVP proceeded at room temperature within 2 hours and
give 90% of the adduct (Scheme 1).10 The PVP was recy-
cled three times further and 88%, 85%, 80% yields were
obtained in the subsequent reactions (Table 1).
Key words: polyvinyl pyridine, aza-Michael reaction, hetero-
geneous solid base
Heterogeneous catalysts have many advantages over their
homogeneous counterparts and hence are the focus of in-
tense research activity. Though extensive work has been
carried out on acidic heterogeneous catalysis the work on
basic heterogeneous catalysis has yet to build momentum.
This is due in part to various of such catalysts being easily
deactivated when exposed to air through CO2 poisoning
(oxides of alkali and alkaline earth metals).
PVP
N
H
COOMe
+
N
r.t.
MeOOC
Among the methods for preparing b-amino carbonyl
compounds, the aza-Michael reaction of nitrogen nucleo-
philes with a,b-unsaturated compounds is very commonly
used.1 Catalysts reported for this reaction include
lanthanide triflates, FeCl3, InCl3, CeCl3/NaI, platinum-
group metal complexes and other Lewis acids.2 However,
these catalysts are not active for the aza-Michael reaction
of carbamates, due to the low nucleophilicity of the of
the carbamate nitrogen. Only a few catalysts such as,
FeCl3·6H2O/Me3SiCl, arylphosphines/Me3SiCl,3 Nafion®,
SAC-13 perfluorinated resin sulfonic acid4 and some
transition-metal salts in their higher valency state5 have
been reported to catalyze such additions. Very recently we
reported that Sn exchanged zeolite Hb as an efficient
catalyst for the one-pot synthesis of carbamates from
amines,6 but no heterogeneous basic polymer catalyst has
yet been reported for this reaction.
Scheme 1 Michael reaction of diethylamine with methyl acrylate in
the presence of PVP
Even bulky amines (entries 2nd and 9th) underwent smooth
addition. Under the same conditions, carbamates also
underwent reaction to give excellent yields of adducts.
In conclusion, we have demonstrated that the conjugate
addition of compounds containing activated double bonds
with secondary amines as well as with less nucleophilic
carbamates can take place at room temperature, in the
presence of PVP, to give high yields of the adducts. No
solvent was needed and the catalyst is recyclable.
Acknowledgment
The Authors thank DST(SP/S1/H06/2000) New Delhi for financial
assistance.
Polymers have been used as catalyst supports for many
years.7 Polyvinyl pyridine (PVP) is a solid basic material,
which can be prepared easily by radical polymerization of
4-vinylpyridine and has been used for preparation of sup-
ported catalysts/reagents in organic transformations.8
However, to date, it has not been used as a heterogeneous
basic catalyst. This prompted us to consider PVP as a
solid heterogeneous catalyst for the aza-Michael reaction
References and Notes
(1) Jung, M. E. In Comprehensive Organic Synthesis, Vol. 4;
Trost, B. M.; Fleming, I., Eds.; Pergamon: Oxford, 1991, 30.
(2) (a) Kawatsuraand, M.; Hartwig, J. W. Organometallics
2001, 20, 1960. (b) Shriwastava, N.; Banik, B. K. J. Org.
Chem. 2003, 68, 2109. (c) Bartoli, G.; Basco, M.;
Marcantoni, E.; Petrini, M.; Sambri, L.; Torregiani, E. J.
Org. Chem. 2001, 66, 9052. (d) Nakama, K.; Seki, S.;
Kanemasa, S. Tetrahedron Lett. 2001, 42, 6719.
(3) Xu, L. W.; Xia, C. G. Tetrahedron Lett. 2004, 45, 4507.
(4) Wabnitz, T. C.; Yu, J. Q.; Spencer, J. B. Synlett 2003, 1070.
(5) Kobayashi, S.; Kakumoto, K.; Sugiua, M. Org. Lett. 2002, 4,
1319.
SYNLETT 2006, No. 16, pp 2676–2678
0
4
.1
0
.2
0
0
6
Advanced online publication: 22.09.2006
DOI: 10.1055/s-2006-949381; Art ID: D00606ST
© Georg Thieme Verlag Stuttgart · New York

LETTER
Recyclable Catalyst for aza-Michael Reaction
2677
Table 1 Aza-Michael Reaction of Secondary Amines and Carbamates with Various Michael Acceptorsa
Substrate
1
Donor
Acceptor
Time (h)
2
Yield (%)b
90
N
COOMe
H
2
3
8
6
75
70
N
H
COOMe
COOMe
N
H
O
4
5
6
1
1
4
90
88
75
COOMe
N
H
O
CN
N
H
O
Me
O
N
H
COOMe
7
8
4
1
75
90
N
H
COOMe
N
H
H
N
9
4
8
80
80
Me
CN
Me
O
10
NHCOOMe
NHCOOMe
Me
O
11
12
13
8
8
8
80
81
77
Me
NHCOOMe
Me
O
NHCOOMe
Me
O
Br
a Reaction conditions: donor = 5 mmol, acceptor = 5.5 mmol, catalyst = 5 wt% of substrate, temp = 30 °C.
b Isolated yield: all compounds were well characterized by 1H NMR and IR spectroscopy.
Synlett 2006, No. 16, 2676–2678 © Thieme Stuttgart · New York

2678
V. P. Raje et al.
LETTER
(6) Raje, V. P.; Bhat, R. P.; Samant, S. D. Tetrahedron Lett.
2005, 45, 835.
(9) Matsuzaki, K.; Matsubara, T.; Kanai, T. J. Polym. Sci. 1977,
15, 1573.
(7) (a) Hodge, P. Ind. Eng. Chem. Res. 2005, 44, 8542.
(b) Akelah, A.; Sherrington, D. C. Polymer 24, 1369.
(8) (a) Shan-Xin, Y.; Zha-Yang; Hecheng, X. Huaxue Bianjbu,
HEHUEZ 1988, 1005 (Chinese) (b) Brunelet, T.; Gelbord,
G.; Geyot, A. Polym. Bull. 1985, 5, 145. (c) Tabacovic, R.;
Tabacovic, I. React. Funct. Polym. 1999, 39, 263.
(d) Alcantara, R.; Canoira, L.; Guilherme-Joao, P.;
Rodriguez, J. G.; Alcantara, E. React. Kinet. Catal. Lett.
2004, 83, 105.
(10) General Reaction Procedure.
To the amine or carbamate (5 mmol) and Michael acceptor
(5.5 mmol) was added PVP (5% by weight on the basis of
amine/carbamate). The reaction mixture was stirred at r.t.
until complete conversion of the starting material. The
reaction mixture was filtered and the catalyst washed with
Et2O. The crude product was purified by column
chromatography. All products were characterized by 1H
NMR and IR spectroscopy.
Synlett 2006, No. 16, 2676–2678 © Thieme Stuttgart · New York