Chitosan: highly efficient, green, and reusable biopolymer catalyst for the synthesis of alkylaminophenols via Petasis borono-Mannich reaction

Article abstract of DOI:10.1016/j.tetlet.2015.07.004

Abstract We screened the catalytic efficacy of different functionalized polymeric catalysts such as nafion 117, PEG-OSO₃H, tween 80, poly styrene -SO₃H and chitosan for the preparation of alkylaminophenols through Petasis borono-Mann

Full text of DOI:10.1016/j.tetlet.2015.07.004

Accepted Manuscript
Chitosan: Highly efficient, green and reusable biopolymer catalyst for the syn-
thesis of alkylaminophenols via Petasis borono-Mannich reaction
Sirigi Reddy Sudharsan Reddy, Bhoomireddy Rajendra Prasad Reddy,
Peddiahgari Vasu Govardhana Reddy
PII:
S0040-4039(15)01134-X
DOI:
http://dx.doi.org/10.1016/j.tetlet.2015.07.004
TETL 46493
Reference:
Tetrahedron Letters
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17 May 2015
26 June 2015
1 July 2015
Please cite this article as: Reddy, S.R.S., Reddy, B.R.P., Reddy, P.V.G., Chitosan: Highly efficient, green and
reusable biopolymer catalyst for the synthesis of alkylaminophenols via Petasis borono-Mannich reaction,
Tetrahedron Letters (2015), doi: http://dx.doi.org/10.1016/j.tetlet.2015.07.004
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Chitosan: Highly efficient, green and reusable
biopolymer catalyst for the synthesis of
alkylaminophenols via Petasis borono-Mannich
reaction
Sirigireddy Sudharsan Reddy, Bhoomireddy Rajendra Prasad Reddy and Peddiahgari Vasu
Govardhana Reddy*
Petasis borono-Mannich reaction was applied to synthesis of alkylaminophenols from o-hydroxy aldehydes, secondary amines and
various boronicacids in presence of chitosan as a heterogeneous green catalyst.

Tetrahedron Letters
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Tetrahedron Letters
journal homepage: www.els evier.com
Chitosan: Highly efficient, green and reusable biopolymer catalyst for the synthesis of
alkylaminophenols via Petasis borono-Mannich reaction
Sirigi Reddy Sudharsan Reddy, Bhoomireddy Rajendra Prasad Reddy and Peddiahgari Vasu Govardhana
∗
Reddy
*Department of Chemistry, Yogi Vemana University, Kadapa-516003, Andhra Pradesh, India.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
We screened the catalytic efficacy of different functionalized polymeric catalysts such as
nafion® 117, PEG-OSO3H, tween® 80, poly styrene -SO3H and chitosan for the preparation
of alkylaminophenols through Petasis borono-Mannich reaction by one-pot three
component condensation of o-hydroxy aldehydes, secondary amines and various boronic
acids. It was observed that the reaction was completed in a short period of time and the
yield was optimum by virtue of chitosan heterogeneous catalyst. Furthermore, the catalyst
can be recovered by simple filtration and reused up to ten cycles. Smooth loss of catalytic
activity was observed from 6th cycle of reuse.
Available online
Keywords:
Nafion® 117
PEG-OSO3H
Tween® 80
Poly styrene -SO3H
Chitosan
Petasis borono-Mannich reaction.
2015 Elsevier Ltd. All rights reserved
1. Introduction
the PBM reaction is necessary. Therefore, Yadav et al.7a reported the
use of ionic liquid to accelerate the PBM reaction. Recently,
Candeias et al.7b also reported that water is a suitable medium for the
reaction, but the procedure needed longer reaction time of 24 h.
Therefore development of new methodologies should take into
consideration for reducing the reaction time, minimum metal
contamination of products, simple reaction conditions, and easy
isolation of products and renewability of catalyst which are highly
desirable for the PBM reaction.
Petasis borono-Mannich (PBM) reaction is a one-step multi
component process, involving an organoboronic acid, an amine, and
a carbonyl derivative, which can produce novel multifunctional
molecules, including geometrically pure allylamines,1a α-
aminoacids,1b,1c
anti-β-amino
alcohols,1d,1e
α-arylglycines,1f
aminophenol derivatives,1g indolyl-N-substituted glycines,1h 2-
hydroxymorpholines,1i α-hydrazino carboxylic acids,1j α-(4-N,N-
dialkylamino-2-alkyloxy phenyl) carboxylic acids1k,1l and aromatic
tertiary amines.1m Among these, the PBM reaction has been the focus
of attention in the last decade because of some features of the
organoboron compounds such as (i) compatibility with many
functional groups allowing the facile synthesis of multifunctional
molecules without the excessive use of protective groups, (ii)
availability of reagents in a large variety of structural configurations,
(iii) possibility of using water and alcohols as the reaction medium,
and (iv) low toxicity and environmental friendliness..2 This PBM
reaction proceeds through condensation of amine and aldehyde to
give the corresponding iminium species followed by intramolecular
transfer of the organyl ligand from the activated ate complex of
organoboronic acid yielding alkylaminophenols.3 The presence of a
hydroxyl group or other coordinating group is essential to form a
boronate, which results in the new carbon-carbon bond after reaction
with the in situ prepared imine.4
Recently, the trends in Science and Technology shown greater
emphasis on eco-friendly and sustainable resources and processes. In
this regard, direct utilization of natural materials for catalytic
applications is a very attractive strategy. In particular, bio polymers
are attractive catalysts to explore the various organic
transformations. Among biopolymers, chitosan is attaining
a
privileged position in various bio-innovation programs. Chitosan is
derived from chitin,8a the second most abundant polysaccharide on
earth after cellulose. Chitin is composed of N-acetyl-D-glucosamine
monomers connected through β (1→4) linkages. Owing to the
presence of readily functionalizable amino groups and hydroxyl
groups in chitosan makes it useful as a chelating agent. It can
activate the nucleophilic as well as electrophilic components of the
reactions by hydrogen bonding and presence of lone pairs
respectively. Recently, chitosan was used in aldol and Knoevenagel
condensation reactions,8b Strecker reaction,8b synthesis of quinoline
derivatives,8d 1, 2, 3-triazole derivatives,8e C-N bond cross
coupling,8f organocatalysis reactions,8g one pot synthesis of pyridine
derivatives8h and green synthesis of heterocycles.8i
In the last few decades, many improved procedures with new
catalysts such as CuBr + bpy, 5a BF3.OEt2,5b InBr3,5c Yb(OTf)3 + Pd
5d
(TFA)2 and 4Å MS.5e have been reported for PBM reaction. In
some cases, hexafluoroisopropanol,6a microwave irradiation6b and
solid phase synthesis6c, 6d were employed in this reaction. However,
these procedures required either a long reaction time or microwave
activation. The development of environmental friendly protocol for
Inspired by these achievements, we surmised that
alkylaminophenols can be synthesized from o-hydroxy aldehydes,
secondary amines and various boronic acids via PBM reaction in the
presence of environmentally benign, easily separable, recyclable and
———
*Corresponding Author. Tel:+91-8562-225410, e-mail: pvgr@yogivemanauniversity.ac.in (P. V. G. Reddy)

acetonitrile, toluene and tetrahydrofuran (THF) as solvents at 80˚C
and reflux conditions for a period of 60 min, 90 min and 3 h
highly effective catalyst system chitosan, further the reaction
conditions like optimization of catalyst and solvent were carried out
and listed in Tables 1 and 2.
produced 85 %, 76 % and 80 % (Table 2, entry e-g) yields
respectively. A moderate yield of 53 % (Table 2, entry h) observed
with 1, 2-dichloroethane (DCE) as solvent at reflux condition for 12
h. A low yield of 22 %, 27 %, 20 % and 21 % (Table 2, entry i-l)
were obtained when we used dimethyl sulfoxide (DMSO), ethanol,
dimethylformamide (DMF) and dimethyl acetamide (DMA) at 80˚C
for 12 h. We also performed the reaction with water at 80˚C for 24 h
produced 55 % of yield (Table 2, entry n). Based on the above results
we concluded that 1, 4-dioxane is the most excellent solvent media
in the case of chitosan catalyzed PBM reaction.
2. Results and Discussion
Initially, we optimized the catalytic efficacy of different
functionalized polymeric catalysts such as nafion® 117, PEG-
OSO3H, tween® 80, poly styrene -SO3H and chitosan (Table 1, entry
a-e) applied for one-pot three component PBM reaction of
salicylaldehyde (1a) (1 mmol), 4-chloro phenyl boronic acid (2a)
(1.2 mmol) and morpholine (3a) (1.1 mmol) in 1, 4-dioxane at 80˚C
as a model reaction (Table 1). Among them chitosan showed best
catalytic activity towards PBM reaction when compared to other
polymeric catalysts. We have tested the PBM reaction with 15 mg
weight of the chitosan to obtain 70% yield of the product in 150 min
(Table 1, entry e). By increasing the loading of the chitosan from 20
mg to 25 mg, improved in yield and reaction rate up to 80 % in 90
min and 95 % in 40 min (Table 1, entry f and g) respectively. It is
remarkable to note that no improvement was observed in the case of
reaction rate and yield by increasing the amount of chitosan beyond
25 mg (Table 1, entry h). Based on these results, 25 mg of the
chitosan is sufficient for PBM reaction.
Table 2: Effect of the solvent on the PBM reactiona
Entry Catalyst
load (mg)
Solvent
Time Temperature Yieldb
(min) (˚C)
(%)
a
b
c
d
e
f
g
h
i
j
k
l
n
25
25
25
25
25
25
25
25
25
25
25
25
25
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
Acetonitrile
Toluene
THF
DCE
DMSO
Ethanol
DMF
24 h
4 h
40
40
60
RT
50
80
100
80
80
reflux
reflux
80
80
80
85
80
95
65
85
76
80
53
22
27
20
21
55
Table 1: Comparison of the catalytic efficacy of chitosan with other
functionalized polymeric catalysts (4a)a
Entry
Catalyst
Catalyst
Load (mg)
Time
Yieldb (%)
90
3 h
a
b
c
d
Nafion® 117
PEG-OSO3H
Tween® 80
Poly styrene
SO3H
25
25
25
25
10 h
12 h
10 h
10 h
65
70
68
73
12 h
12 h
12 h
12 h
12 h
24 h
-
DMA
Water
80
80
e
f
g
h
Chitosan
Chitosan
Chitosan
Chitosan
15
20
25
30
150 min
90 min
40 min
40 min
70
80
95
95
aReaction of salicylaldehyde (1a) (1 mmol), 4-chloro phenylboronic acid (2a)
(1.2 mmol) and morpholine (3a) (1.1 mmol) in presence of chitosan (25 mg)
in different solvents at various temparatures.
bIsolated yield
aReaction of salicylaldehyde (1a) (1 mmol), 4-chloro phenylboronic acid (2a)
(1.2 mmol) and morpholine (3a) (1.1 mmol) in presence of different
polymeric catalysts in 1, 4-dioxane at 80 ˚C.
bIsolated yield
OH
OH
Chitosan
HO
B
Ar
Ar
HO
R
1, 4-Dioxane
80oC
R
CHO
N
H
N
2
R1
R2
1
R1
R2
4 (a-s)
3
H
H
N
H
N
HO
N
H
N
NH2
O
NH2
O
=
HO
O
HO
O
O
O
R1
R2
HO
O
O
NH2
HO
HO
n
Chitosan
R=H and CH3
Scheme 1: Chitosan catalyzed PBM reaction
Further, we also screened the PBM reaction by employing
salicylaldehyde (1a), 4-chloro phenylboronic acid (2a) and
morpholine (3a) in various solvents and chitosan as a catalyst at
different temperatures as shown in the Table 2. First we performed
the reaction in 1, 4-dioxane (5 mL) by loading chitosan (25 mg) at
ambient temperature for 24 h to obtain the 85% of alkylaminophenol
(Table 2, entry a). To reduce the reaction time, we performed the
reaction at various temperatures such as 50˚C and 80˚C with same
amount of catalyst yielding the alkylaminophenol in 80 % and 95 %
(Table 2, entry b and c) for 4 h and 40 min respectively. Further
increasing the temperature to 100˚C led to decrease in yield of 65 %
(Table 2, entry d). When the same reaction was carried out in
Fig.1 The recyclability of chitosan in ten cycles for the PBM
reaction of salicylaldehyde (1a), 4- chloro phenylboronic acid (2a)
and morpholine (3a).
Having identified the optimal reaction conditions, we sought to
evaluate the scope and efficiency of the reaction. For this purpose, a
broad range of structurally varied o-hydroxy aldehydes, secondary
amines and aryl boronic acids were chosen to perform the PBM
reaction to yield the corresponding alkylaminophenols (4a-s) and the
results were displayed in Table 3. With regard to the various boronic
acids bearing both electron donating and withdrawing substituents
can be efficiently converted into alkylaminophenols in high yields as

Tetrahedron Letters
4
Table 3: Chitosan catalysed synthesis of alkylaminophenolsa
Entry
Aldehyde
(1 a-b)
Boronic acid
(2 a-m)
Amine
(3 a-c)
Product
(4 a-s)
OH
Time
(min)
Yieldb
(%)
Cl
40
95
OH
H
N
B(OH)2
a
CHO
N
O
1 a
1 a
1 a
1 a
3 a
2 a
4 a
Cl
O
OH
OCH3
40
92
OH
H
N
B(OH)2
b
c
d
CHO
N
O
O
3 a
2 b
4 b
OCH3
OH
45
44
40
50
87
90
90
89
OH
B(OH)2
H
N
S
CHO
N
S
O
3 a
2 c
4 c
O
OH
B(OH)2
OCH3
OH
H
N
OCH3
CHO
OCH3
N
O
O
OCH3
4 d
3 a
2 d
H
N
OH
OH
OCH3
(HO)2B
e
CHO
O
OCH3
N
O
1 a
3 a
2 e
4 e
H
N
OH
OH
f
B(OH)2
O
CHO
O
N
O
1 a
1 a
1 a
3 a
2 f
4 f
O
H
N
OH
B(OH)2
OH
g
h
i
45
45
50
43
93
90
86
91
CHO
OCH3
O
OCH3
N
3 a
4 g
2 g
O
OH
OH
H
N
B(OH)2
CHO
O
N
O
3 a
2 h
4 h
H
N
OH
B(OH)2
OH
S
H3CO
CHO
H3CO
S
O
N
1 b
2 c
4 i
3 a
O
OH
OCH3
H
N
OH
B(OH)2
j
H3CO
N
O
H3CO
CHO
O
4 j
1 b
2 b
3 a
OCH3

B(OH)2
H
N
OH
OCH3
OCH3
OH
45
90
k
H3CO
H3CO
CHO
O
N
O
OCH3
1 b
3 a
4 k
OCH3
2 d
B(OH)2
H
N
OH
OH
45
40
88
l
H3CO
CHO
H3CO
O
N
1 b
2 h
3 a
4 l
O
OH
B(OH)2
CH3
H
N
OH
95
m
CHO
O
N
O
CH3
2 i
1 a
3 a
4 m
B(OH)2
CH3
H
N
OH
OH
n
o
45
40
91
CHO
N
CH3
2 i
1 a
3 b
4 n
B(OH)2
H
N
OH
OH
CH3
95
CHO
O
3 a
N
1 a
4 o
2 j
CH3
O
B(OH)2
H
N
OH
OH
p
q
45
50
90
CHO
NO2
O
NO2
N
1 a
3 a
4 p
2 k
O
OH
OH
B(OH)2
H
N
93
CHO
N
2 l
3 c
1 a
4 q
B(OH)2
OCH3
H
N
OH
OH
OCH3
r
50
89
87
CHO
H3CO
OCH3
OCH3
OCH3
O
N
O
1 a
3 a
2 m
4 r
OCH3
OCH3
B(OH)2
s
50
OH
CHO
H
N
OH
N
H3CO
OCH3
OCH3
OCH3
1 a
3 b
2 m
4 s
aReaction of o-hydroxy aldehydes (1 a-b) (1 mmol), secondary amines (2 a-c) (1.1 mmol) and various boronic acids (3 a-h) (1.2 mmol)
in presence of chitosan (25 mg) in 1, 4-dioxane (5 mL) at 80˚C.
bIsolated yield
shown in the Table 3. All the products were characterized by IR, (1H
&13C) NMR spectra and elemental analyses. The resulting
alkylaminophenols were obtained as racemates and these are
evidenced by 1: 1 ratio peaks in chiral HPLC.
In addition, we tested the efficiency of the catalyst in terms of the
reusability in the PBM reaction. After completion of the reaction, the
catalyst was simply filtered, washed with ethyl acetate and dried at
80oC. Catalyst recycling experiments were carried out with repeated
use for further ten more consecutive reactions between
salicylaldehyde, morpholine and 4-chloro phenylboronic acid to
yield the alkylaminophenol. Smooth loss of catalytic activity was
observed from 6th cycle of reuse as showed in the Fig 1.
These results led us to tentatively assign a mechanism for the
process. The free hydroxyl and amino groups distributed on the
surface of chitosan in high concentration activates the carbonyl
group of the salicylaldehyde through hydrogen bonding for
nucleophilic attack of amines to produce the corresponding
iminiumion intermediate (IM-1). Coordination between the oxygen
anion of phenolate and the boron atom of boronic acid leads to the
formation of a tetra coordinate borate intermediate. Subsequently,

Tetrahedron Letters
6
the aryl carbanion moiety of boronic acid favourably attacks the
Supporting information
iminium ion forming the stable intermediate (IM-2) which upon
hydrolysis furnished the desired product by the loss of H3BO3
molecule. Here chitosan plays a key role in the formation of iminium
ion intermediate (IM-1) (Scheme 2).
Supplementary data of all 1H and 13C NMR spectra associated with
article can be found in the online version at
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Acknowledgements
The authors are thankful to the Board of Research in Nuclear
Sciences (BRNS), Mumbai, India for providing the financial support
(NO. 2012/37C/33/BRNS). We also acknowledge the support of
University Grants Commission (UGC), New Delhi for providing
Junior Research Fellowship (JRF) to S.S.Reddy.

2015, 56, 1919-1924; (i) Sahu, P. K.; Sahu, P. K.; Gupta,
S. K.; Agarwal, D. D. Ind. Eng. Chem. Res. 2014, 53,
2085-2091.

Tetrahedron Letters
8
Highlights
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•
•
•
First time we reported the chitosan
catalyzed Petasis Borono-Mannich reaction.
Short reaction time, high conversions and
recyclability of the catalyst.
The plausible mechanism of chitosan
catalyzed PBM reaction is proposed.
Synthesis of chiral alkylaminophenols for
the same racemates is under progress.