An efficient green synthesis of a new class of α-aminophosphonates under microwave irradiation conditions in the presence of PS/PTSA

Article abstract of DOI:10.1002/hc.21147

The present work focuses on the study of catalytic activity of polystyrene-supported p-toluenesulfonic acid (PS/PTSA) and the synthesis of α-aminophosphonates from the Kabachnik-Fields (KF) reaction under microwave irradiation in solvent-free conditions. Recently, the catalytic activity of PS/PTSA was tested with good yields. This procedure is the simplest, most straightforward, environment friendly method for the synthesis of α-aminophosphonates from simple to different substituted aldehyde substrates. Furthermore, this catalyst can be recovered and reused without loss of its catalytic activity.

Full text of DOI:10.1002/hc.21147

Heteroatom Chemistry
Volume 00, Number 00, 2014
An Efficient Green Synthesis of a New Class
of α-Aminophosphonates under Microwave
Irradiation Conditions in the Presence of
PS/PTSA
Chandra Sekhar Reddy Gangireddy,1–3 Radha Rani Chinthaparthi,2,3
Veeranarayana Reddy Mudumala,2 Madhav Mamilla,3
and Uma Ravi Sankar Arigala2
1Department of Chemistry, Sri Venkateswara College of Engineering, Tirupati 517 507, India
2Department of Chemistry, Sri Venkateswara University, Tirupati 517 502, India
3Department of Chemistry, Sri Venkateswara Degree & PG College, Kadapa 16 003, India
Received 13 June 2013; revised 31 January 2014
INTRODUCTION
ABSTRACT: The present work focuses on the
study of catalytic activity of polystyrene-supported
p-toluenesulfonic acid (PS/PTSA) and the synthesis of
α-aminophosphonates from the Kabachnik–Fields
(KF) reaction under microwave irradiation in solvent-
free conditions. Recently, the catalytic activity of
PS/PTSA was tested with good yields. This pro-
cedure is the simplest, most straightforward, en-
vironment friendly method for the synthesis of
α-aminophosphonates from simple to different sub-
stituted aldehyde substrates. Furthermore, this cat-
alyst can be recovered and reused without loss
The formation of the phosphorus–carbon bond has
attracted much attention because phosphonates
have wide applications in organic synthesis and
bioorganic chemistry. α-Functionalized phosphonic
acid esters serve as valuable intermediates for the
preparation of synthetic intermediates [1–4] and
antibacterial/viral/inflammatory and cancer drugs
[5–7]. The synthesis of α-aminophosphonates using
Bro¨nsted and Lewis acids, heteropoly acids, hetero-
geneous catalysts, microwave irradiation (MWI), ul-
trasound irradiation, catalyst free, ionic liquid, and
nanocatalysts has been reported [8–17] by using the
Kabachnik–Fields (KF) reaction [18–20].
Several green chemical synthetic approaches us-
ing the KF reaction are reported in solvent- and
catalyst-free conditions [21–24], solvent-free un-
der MWI using [25–32] heterocyclic amines, oxo-
component, and >P(O)H species [33–35]. All of
these reports are based on few model reactions [22,
36, 37]. Later phospha-Mannich condensation [36–
38] was further improvised in microwave-heated
solvent- and catalyst-free conditions. Recently, all
the microwave-assisted KF reactions in a simple,
straightforward, and most environmentally friendly
way were revised elaborately under solvent- and
ꢀC
of its catalytic activity.
2014 Wiley Periodi-
cals, Inc. Heteroatom Chem. 00:1–10, 2014; View
this article online at wileyonlinelibrary.com. DOI
10.1002/hc.21147
Correspondence to: Chandra Sekhar Reddy Gangireddy; e-mail:
drcsreddyg@gmail.com.
Contract grant sponsor: Department of Science and Technol-
ogy, Government of India, New Delhi, India.
Contract grant number: CS/014/2013.
ꢀC
2014 Wiley Periodicals, Inc.
1

2
Gangireddy et al.
SCHEME 1 Model synthetic reaction of dimethyl (((9H-fluoren-2-yl)amino)(4-fluorophenyl)methyl)phosphonate (4a).
catalyst-free reaction conditions [39, 40]. Our study
group has already reported a simple, convenient,
mild and fast procedure for the KF reaction [23]
in solvent-free MWI conditions using alumina and
montmorillonite K-10 as a solid-supported catalyst.
We achieved good results in all these reactions.
Although significant advances have been made in
the reported syntheses, still there are several limita-
tions such as the use of expensive and toxic solvents
and catalysts, a longer reaction time, high temper-
ature, and low yields. Therefore, a better synthetic
procedure for their synthesis is warranted.
advantages has not been exploited fully in organic
synthesis [45–47].
Eventually, a better one-pot synthetic procedure
for α-aminophosphonates in terms of operational
simplicity, economic viability, and greater selectivity
by the KF reaction of 2-aminofluorene, an aldehyde,
and a dimethyl phosphite in the presence of a cat-
alytic amount (5 mol%) of PS/PTSA under solvent-
free MWI conditions is accomplished.
RESULTS AND DISCUSSION
A
solid-supported
catalyst
polystyrene
The reaction conditions are optimized for the
model reaction between 2-aminofluorene (1), 4-
fluorobenzaldehyde (2a), and dimethyl phosphite (3)
to afford α-aminophosphonate (4a) under solvent-
free conditions (Scheme 1), employing different cat-
alysts under both conventional heating and MWI
conditions (Table 1).
p-toluenesulfonic acid (PS/PTSA) complex with
a number of advantages such as improving the
availability of active sites, stability, hygroscopic
properties, handling, reusability, and good product
yields [21,41–44] was selected and used as a catalyst
in this reaction. This catalyst despite of its great
TABLE 1 Optimization of Required Catalyst and Reaction Conditionsa of 4a
Conventional Heating
MWI
Temperature (°C)
Entry
Catalyst (mol%)
Temperature (°C)
Time (min)
Yieldb (%)
Yieldb (%)
1
2
3
4
5
6
7
8
Catalyst free
Catalyst free
Catalyst free
InF3 (10)
CAN-SiO2 (10)
ZnCl2-SiO2 (10)
MnCl2·4H2O (10)
Yb(OAc)3·H2O (10)
CuBr (10)
NbCl5 (10)
FePO4 (10)
Al2O3 (10)
PTSA (10)
PS/GaCl3 (10)
PS/AlCl3 (10)
PS/PTSA (10)
PS/PTSA (10)
PS/PTSA (5)
PS/PTSA (3)
r.t.
100
120
90
90
90
90
90
90
90
90
90
90
90
90
90
70
90
90
24 h
180
180
120
120
130
110
140
120
100
100
120
100
80
12
22
26
25
30
25
55
40
29
50
55
50
55
75
80
82
76
81
75
70
150
180
90
90
90
90
90
90
90
90
90
90
90
90
90
70
70
90
19
34
40
40
45
35
60
40
35
60
65
60
70
80
82
97
9
10
11
12
13
14
15
16
17
18c
19
75
55
55
55
96
96,95,93, 90
85
55
aReaction conditions: 2-Aminofluorene (1), 4-methylbenzaldehyde (2a), and dimethyl phosphite (3) at equimolar ratio, and 20 min (for entries
1 and 3), 10 min (for entries 4–16) and 5 min (for entries 17–19) reaction time in solvent-free and MWI conditions (at 210 W).
bIsolated yield.
cCatalyst recovery.
Heteroatom Chemistry DOI 10.1002/hc

Synthesis of α-Aminophosphonates under Microwave Irradiation Conditions in the Presence of PS/PTSA
3
TABLE 2 Optimization of MW Powera for the Synthesis of
found that the yield of the products was 81% under
conventional conditions and 96% under MWI with
5 mol% of the PS/PTSA catalyst in 55 and 5 min,
respectively (Table 1, entry 18). Therefore, 5 mol%
of PS/PTSA was found necessary and sufficient for
the total completion of the model reaction in both
conditions. The reaction remains incomplete with
3 mol% of the catalyst (Table 1, entry 19).
To check the reusability of the catalyst, the same
reaction was run with fresh and isolated PS/PTSA
for three consecutive cycles in the preparation of
α-aminophosphonate (4a) and in all the three con-
secutive reactions the yield of α-aminophosphonates
was 95%, 93%, and 90% (Table 1, entry 18). The
PS/PTSA was recovered from the reaction mixture
by dissolving it in hot EtOH and filtration. These
data demonstrate high stability and reusability of
the catalyst under these reaction conditions.
4a
Entry
MW Power
(W)
Temperature
Time
(min)
Yieldb
(%)
(°C)
1
2
3
4
5
6
7
8
140
245
140
210
210
245
280
350
490
700
90
140
90
120
70
140
170
210
245
340
30
20
10
10
5
5
5
5
5
5
20
38
88
97
96
90
84
81
64
10
9
10
aReaction conditions: An equimolar ratios of 2-aminofluorene (1), 4-
methylbenzaldehyde (2a), and dimethyl phosphite (3) in catalyst-free
conditions (entries 1 and 2) and 5 mol% of PS/PTSA catalyst (entries
3–10).
bIsolated yield.
The model reaction was also studied at various
MW conditions to choose the best irradiation condi-
tion with and without 5 mol% of the PS/PTSA cat-
alyst. Even in the absence of the catalyst, a signif-
icant yield of the product was recorded (Table 2,
entries 1 and 2); it is not a sufficient reaction condi-
tion because of the requirement of higher reaction
temperature for a prolonged period. While using the
PS/PTSA catalyst, excellent product yield was possi-
ble in a short reaction time at lower reaction tem-
perature (4a; Table 2, entry 5). It was found that
at 210 W MWI 70°C for 5 min with 5 mol% of
catalyst is ideal to accomplish maximum conversion
of reactants to products. Increasing the MWI power
decreases the product yield due to overheating and
formation of char residue (Table 2, entry 10).
Initially, the model reaction was carried without
any catalyst, resulting in poor yields (Table 1, en-
tries 1–3). This reaction, when conducted using InF3,
CAN-SiO2, and ZnCl2-SiO2, produced very low yields
(Table 1, entries 4–6). Although catalysts such as
MnCl2·4H2O, Yb(OAc)3, CuBr, NbCl5, FePO4, Al2O3,
and PTSA promoted the reaction to a considerable
extent, the yield of compounds was not satisfac-
tory (Table 1, entries 7–13). But polymer-supported
Lewis acid catalysts such as PS/GaCl3, PS/AlCl3, and
PS/PTSA (Table 1, entries 14–16) worked efficiently.
Among them, PS/PTSA showed excellent catalytic
activity under MWI conditions even at lower tem-
perature (Table 1, entries 17). All these catalytic re-
actions were carried out with 10 mol% of the cata-
lyst. To assert the minimum optimum concentration
of the PS/PTSA catalyst, the same reaction was car-
ried out with 5 and 3 mol% concentrations. It was
To ascertain the effect of solvent and tempera-
ture in catalyst-free and 5 mol% of PS/PTSA catalyst
conditions, the model reaction was run under both
TABLE 3 Optimization of Solvent and Temperaturea for the Synthesis 4a
Conventional Heating
Yieldb (%)
MWI
Yieldb (%)
Entry
Solvent
Toluene
Chlorobenzene
Ethanol
Acetonitrile
THF
CCl4
Temperature (°C)
Catalyst-Free
PS/PTSA
Temperature (°C)
Catalyst-Free
PS/PTSA
1
2
3
4
5
6
7
8
110
130
75
80
65
75
90
150
38.4
37.2
42.1
43.6
42.8
41.4
18.1
25.3
64.6
65.7
64.4
66.8
67.4
65.2
66.2
69.5
110
130
75
80
65
75
70
110
61.9
62.8
65.6
66.2
65.7
60.7
60.3
63.8
90.3
91.1
78.5
82.6
85.4
73.4
96.4
97.6
Solvent-free 1
Solvent-free 2
aReaction conditions: 2-Aminofluorene (1), 4-methylbenzaldehyde (2a), and dimethyl phosphite (3) in a 1:1:1 molar ratio using 5 mol% PS/PTSA
catalyst. All the reactions are carried out by 55 and 5 min, respectively, in conventional heating and MWI (at 210 W) conditions.
bIsolated yield.
Heteroatom Chemistry DOI 10.1002/hc

4
Gangireddy et al.
FIGURE 1 Optimization of solvent and temperature for the synthesis of 4a–r in both conventional heating and MWI.
SCHEME 2 PS/PTSA-MWI synthesis of 4a–r.
conventional and MW (210 W) heating in different
solvents for 55 and 5 min, respectively. Irrespective
of the nature of the solvent, the yield of the products
was low (Table 3, entries 1–6). But under solvent-
free conditions, better yield of product resulted
(Table 3, entries 7 and 8). The poor yields in the
solvent medium may be attributed to solvation of
the substrates in the reaction medium. Therefore, it
is established that MWI at 70°C without the solvent
is the best condition for this reaction (Fig. 1).
Under the optimized experimental reaction con-
ditions, 5 mol% of PS/PTSA, MW heating at 210 W,
70°C, 5–7 min in solvent-free conditions, a num-
ber of aldehydes (2b–r) successfully reacted with
2-aminofluorene (1) and dimethyl phosphite (3)
and produced corresponding α-aminophosphonates
(4b–r; Scheme 2) in excellent yields (Table 4).
Interestingly, aromatic aldehydes with electron-
withdrawing substituents gave products with com-
parable yields when compared to those having
Heteroatom Chemistry DOI 10.1002/hc

Synthesis of α-Aminophosphonates under Microwave Irradiation Conditions in the Presence of PS/PTSA
5
TABLE 4 MWI Synthesis of 4a–r with PS/PTSA as a
also occurred smoothly, but the yield of products,
though good, is lower than those with aromatic alde-
hydes (2a–m; Table 4, entries 1–13). Various other
aldehydes with different functional groups were also
found to react under these conditions. In general, the
reaction with different substituents in the aldehydes
was almost quantitative, and no side products are
formed.
Catalysta
Compound
Time (min)
Yieldb (%)
Reference
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
5
5
5
5
6
6
5
5
5
4
6
5
6
6
7
7
6
7
95
98
98
95
94
92
95
93
93
96
94
95
92
88
88
86
86
84
CONCLUSIONS
We have successfully developed a simple, green,
and efficient MW-assisted one-pot multicomponent
KF synthesis of α-aminophosphonates from eas-
ily available starting materials using PS/PTSA as a
solid-supported catalyst under solvent-free condi-
tions. Even though catalyst-free KF reactions are re-
ported, here we report the use of solid-supported
PS/PTSA as an effective catalyst. The reactivity of
2-aminofluorene, dimethyl phosphite, and various
aldehydes not only accelerated under MWI condi-
tions in the presence of PS/PTSA but also afforded
excellent yields. Therefore, this method serves as an
attractive one for industries for the synthesis of var-
ious functionalized α-aminophosphonates.
[6]
[6]
aReaction conditions: 2-Aminofluorene (1), various aldehydes (2a–r),
and dimethyl phosphite (3) using 5 mol% a PS/PTSA catalyst at 210
W in neat conditions.
bIsolated yields.
EXPERIMENTAL
Materials and Methods
All the chemicals procured from Sigma–Aldrich
(Hyderabad, India), Merck (Mumbai, India), and
Lancaster Chemical (Mumbai, India) were used as
such without further purification. All solvents used
for spectroscopic and other physical studies were of
reagent grade and were further purified by employ-
ing the reported methods. Melting points were de-
termined using a calibrated thermometer by a Guna
Digital melting point apparatus. IR spectra were
recorded on a Sumhazud IR Prestige-21, Fourier
transform infrared spectrometer with a scanning
range of 400–4000 cm−1 for 32 scans at a spectral
resolution of 4 cm−1 using KBr optical disks. 1H,
13C, and 31P NMR spectra were recorded in CDCl3
on a Varian 400 MHz NMR spectrometer operating
at 400 MHz for 1H NMR, 100 MHz for 13C NMR, and
161.89 MHz for 31P NMR at Pusan National Univer-
sity, Pusan, Republic of Korea, and referenced to
TMS (1H and 13C) and 85% H3PO4 (31P). Mass spec-
tra were recorded on a Jeol JMS-700 mass spectrom-
eter at Pukyong National University, Busan, Repub-
lic of Korea. Elemental analyses were performed on
a Thermo Finnigan instrument at the University of
Hyderabad, Hyderabad, India.
SCHEME 3 Mechanistic pathway for one-pot KF synthesis
of 4a–r with PS/PTSA as a catalyst.
electron-donating groups. The negative inductive ef-
fect resulted in a stronger electrophilic center at
the carbonyl carbon, which facilitates the addition
of amines to the carbonyl carbon to form imines
that subsequently unites with the nucleophilic phos-
phonate phosphorus (Scheme 3). The reaction with
aliphatic aldehydes (2n–r; Table 4, entries 14–18)
Heteroatom Chemistry DOI 10.1002/hc

6
Gangireddy et al.
3
3
General Method for the Synthesis of Dimethyl
(((9H-fluoren-2-yl)amino)(4-fluorophenyl)
methyl)phosphonate (4a) by MWI
d, JH-P = 10.4 Hz, P OCH3), 3.77 (3H, d, JH-P
=
10.4 Hz, P OCH3), 3.73 (2H, s, Ar CH2 Ar), 6.57–
6.59 (1H, dd, 2JH-P = 8.4 Hz, P-CH and 3JH-H = 2.0 Hz,
NH CH), 6.74 (1H, m, NH), 7.13–7.58 (11H, m,
Ar H). IR (KBr) (νmax cm−1): 3305 (N H), 2956 and
2867 (C Haromatic), 1259 (P O), 763 (P Caliphatic).
EI-MS m/z (%): 397 (12) M+•. Anal. Calcd for
C22H21FNO3P: C, 66.49; H, 5.33; N, 3.52; Found: C,
66.37; H, 5.26; N, 3.45.
2-Aminofluorene (1, 0.90 g, 0.005 mol), 4-fluoro-
benzaldehyde (2a, 0.62 g, 0.005 mol), dimethyl phos-
phite (3, 0.46 mL, 0.005 mol), and various catalysts
in 3, 5, and 10 mol% were mixed thoroughly in a two-
necked 25-mL round-bottomed (RB) flask, which
was fitted with an air condenser in one neck and a
thermo probe at the other neck and was exposed to
140–700 W MWI using a synthetic microwave oven
CATA-4R-Scientific MW oven (Catalyst Systems) at
70–340°C at ambient pressure. The reaction mix-
ture was stirred continually while irradiating with
MW radiation to maintain uniform temperature. By
monitoring with TLC, the reaction was stopped after
5–7 min. Then chloroform (3 × 5 mL) was added to
the RB flask, and PS/PTSA was separated by filtra-
tion to recover the catalyst. The crude reaction prod-
ucts obtained by evaporation of filtrate were purified
by column chromatography on 60–120 mesh silica
gel using ethyl acetate:hexane (1:3) as an eluent, and
the solvent was evaporated in a rotary evaporator.
The residue was recrystallized from ethyl acetate to
afford pure 4a (Table 1).
All the other compounds (4b–r) were prepared
by following the procedure with 5 mol% PS/PTSA at
70°C of 210 W of MWI at ambient pressure (Scheme
2). The reaction was successfully completed in
3–5 min and afforded 4b–r in high yields (Ta-
ble 2). The structures of all the newly synthesized
compounds were characterized by IR, 1H NMR,
13C NMR, 31P NMR, mass spectral, and elemental
analysis.
Dimethyl (((9H-fluoren-2-yl)amino)(p-tolyl)me-
thyl) phosphonate (4b). White solid, mp: 178–
120°C. 31P NMR (161.89, MHz, CDCl3) δ: 21.27; 13C
NMR (100.56 MHz, CDCl3) δ: 114.3 (C-1), 150.7 (C-
2), 108.6 (C-3), 121.5 (C-4), 122.5 (C-5), 127.7 (C-
6), 128.2 (C-7), 126.7 (C-8), 37.3 (C-9), 145.7 (C-10),
129.6 (C-11), 138.4 (C-12), 140.2 (C-13), 56.3 (C-15),
131.4 (C-16), 128.2 (C-17 and C-21), 126.6 (C-18 and
C-20), 138.6 (C-19), 22.4 (Ar CH3), 52.2 (P OCH3),
1
53.3 (P OCH3); H NMR (400 MHz, CDCl3) δ: 2.15
3
(3H, s, Ar CH3), 3.51 (3H, d, JH-P = 10.4 Hz,
3
P
OCH3), 3.73 (3H, d, JH-P = 10.4 Hz, P OCH3),
3.70 (2H, s, Ar CH2 Ar), 6.53–6.56 (1H, dd, 2JH-P
=
3
8.4 Hz, P CH and JH-H = 2.0 Hz, NH CH),
6.74 (1H, m, NH), 7.12–7.56 (11H, m, Ar H). IR
(KBr) (νmax cm−1): 3311 (N H), 2960 and 2859
(C Haromatic), 1229 (P O), 763 (P Caliphatic). EI-MS
m/z (%): 393 (10) M+•. Anal. Calcd. for C23H24NO3P:
C, 70.22; H, 6.15; N, 3.56; Found: C, 70.15; H, 6.08;
N, 3.49.
Dimethyl (((9H-fluoren-2-yl)amino)(4-methoxy-
phenyl) methyl)phosphonate (4c). Brown solid, mp:
187–189°C. 31P NMR (161.89, MHz, CDCl3) δ: 21.37;
13C NMR (100.56 MHz, CDCl3) δ: 115.1 (C-1), 151.3
(C-2), 108.2 (C-3), 122.1 (C-4), 121.9 (C-5), 127.8 (C-
6), 128.3 (C-7), 126.5 (C-8), 37.7 (C-9), 145.2 (C-10),
129.1 (C-11), 138.7 (C-12), 140.8 (C-13), 56.5 (C-15),
130.8 (C-16), 127.1 (C-17 and C-21), 114.1 (C-18 and
C-20), 158.3 (C-19), 55.7 (OCH3), 52.6 (P OCH3),
Conventional Heating Method for the Synthesis
of 4a. On the other hand, in conventional heating
method, all the above reactants were heated in an oil
bath at 65–130°C for 55–140 min, and the workup
and purification of products were carried out in a
similar way by following the MWI procedure.
1
53.7 (P OCH3); H NMR (400 MHz, CDCl3) δ: 3.79
3
(3H, s, Ar OCH3), 3.57 (3H, d, JH-P = 10.4 Hz,
3
P
OCH3), 3.87 (3H, d, JH-P = 10.4 Hz, P OCH3),
3.73 (2H, s, Ar CH2 Ar), 6.57–6.61 (1H, dd, 2JH-P
=
Physical and Spectral Characteristics of 4a–r.
3
8.4 Hz, P CH and JH-H = 2.0 Hz, NH CH),
6.61 (1H, m, NH), 7.25–7.69 (11H, m, Ar H). IR
(KBr) (νmax cm−1): 3314 (N H), 2967 and 2866
(C Haromatic), 1258 (P O), 756 (P Caliphatic). EI-MS
m/z (%): 409 (16) M+•. Anal. Calcd. for C23H24NO4P:
C, 67.47; H, 5.91; N, 3.42; Found: C, 67.35; H, 5.85;
N, 3.46.
Dimethyl (((9H-fluoren-2-yl)amino)(4-fluorophe-
nyl) methyl)phosphonate (4a). Brown solid, mp:
155–157°C. 31P NMR (161.89, MHz, CDCl3) δ: 21.07;
13C NMR (100.56 MHz, CDCl3) δ: 114.7 (C-1), 150.4
(C-2), 108.3 (C-3), 121.4 (C-4), 122.3 (C-5), 127.5
(C-6), 128.4 (C-7), 126.8 (C-8), 37.5 (C-9), 145.6 (C-
10), 129.2 (C-11), 138.1 (C-12), 140.4 (C-13), 56.4
(C-15), 131.9 (C-16), 130.4 (C-17 and C-21), 116.4
(C-18 and C-20), 163.2 (C-19), 52.5 (P OCH3), 53.4
(P OCH3); 1H NMR (400 MHz, CDCl3) δ: 3.55 (3H,
Dimethyl (((9H-fluoren-2-yl)amino)(3-methoxy-
phenyl) methyl)phosphonate (4d). Brown solid, mp:
192–194°C. 31P NMR (161.89, MHz, CDCl3) δ:
Heteroatom Chemistry DOI 10.1002/hc

Synthesis of α-Aminophosphonates under Microwave Irradiation Conditions in the Presence of PS/PTSA
7
1
21.32; 1H NMR (400 MHz, CDCl3) δ: 3.82 (3H, s,
Ar OCH3), 3.59 (3H, d, 3JH-P = 10.4 Hz, P OCH3),
53.6 (P OCH3); H NMR (400 MHz, CDCl3) δ: 3.52
3
(3H, d, JH-P = 10.4 Hz, P OCH3), 3.64 (3H, d,
3
3.84 (3H, d, JH-P = 10.4 Hz, P OCH3), 3.75 (2H,
3JH-P = 10.4 Hz, P OCH3), 4.32 (4H, s, O(CH2)2O),
2
2
s, Ar CH2 Ar), 6.55–6.60 (1H, dd, JH-P = 8.4 Hz,
6.48–6.13 (1H, dd, JH-P = 8.4 Hz, P CH and
3
P-CH and JH-H = 2.0 Hz, NH CH), 6.62 (1H, m,
3JH-H = 2.0 Hz, NH CH), 6.63 (1H, m, NH), 7.16–
7.52 (10H, m, Ar H). IR (KBr) (νmax cm−1): 3318
(N H), 2964 and 2863 (C Haromatic), 1230 (P O),
757 (P Caliphatic). EI-MS m/z (%): 437 (8) M+•. Anal.
Calcd. for C24H24NO5P: C, 65.90; H, 5.53; N, 3.20;
Found: C, 65.85; H, 5.48; N, 3.15.
NH), 7.21–7.65 (11H, m, Ar H). IR (KBr) (νmax
cm−1): 3314 (N H), 2967 and 2867 (C Haromatic),
1258 (P O), 757 (P Caliphatic). Anal. Calcd. for
C23H24NO4P: C, 67.47; H, 5.91; N, 3.42; Found: C,
67.34; H, 5.82; N, 3.47.
Dimethyl (((9H-fluoren-2-yl)amino) (benzo[d]-
[1,3]dioxol-5-yl)methyl)phosphonate (4h). Brown
solid, mp: 196–198°C. 31P NMR (161.7, MHz, CDCl3)
δ: 20.65; 13C NMR (100.56 MHz, CDCl3) δ: 113.7
(C-1), 150.7 (C-2), 109.8 (C-3), 121.1 (C-4), 122.6
(C-5), 127.7 (C-6), 129.1 (C-7), 126.7 (C-8), 36.5
(C-9), 145.3 (C-10), 129.4 (C-11), 138.2 (C-12), 141.1
(C-13), 57.4 (C-15), 128.7 (C-16), 119.6 (C-17), 111.7
(C-18), 96.9 (C-20), 111.7 (C-22), 149.2 (C-23), 145.7
(C-24), 52.5 (P OCH3), 53.7 (P OCH3); 1H NMR
Dimethyl (((9H-fluoren-2-yl)amino)(4-chlorophe-
nyl) methyl)phosphonate (4e). Pale yellow solid,
mp: 170–172°C. 31P NMR (161.89, MHz, CDCl3)
δ: 20.51; 13C NMR (100.56 MHz, CDCl3) δ: 114.2
(C-1), 150.5 (C-2), 108.4 (C-3), 121.1 (C-4), 122.7
(C-5), 127.5 (C-6), 128.6 (C-7), 126.9 (C-8), 37.3 (C-
9), 145.5 (C-10), 129.3 (C-11), 138.5 (C-12), 140.7
(C-13), 56.5 (C-15), 131.7 (C-16), 129.7 (C-17 and
C-21), 115.6 (C-18 and C-20), 161.3 (C-19), 52.4
(P OCH3), 53.1 (P OCH3); 1H NMR (400 MHz,
3
3
(400 MHz, CDCl3) δ: 3.50 (3H, d, JH-P = 10.4 Hz,
CDCl3) δ: 3.53 (3H, d, JH-P = 10.4 Hz, P OCH3),
3
3
P
OCH3), 3.62 (3H, d, JH-P = 10.4 Hz, P OCH3),
3.77 (3H, d, JH-P = 10.4 Hz, P OCH3), 3.65 (2H,
2
2
5.83 (4H, s, OCH2O), 6.52–6.18 (1H, dd, JH-P
=
s, Ar CH2 Ar), 6.55–6.56 (1H, dd, JH-P = 8.4 Hz,
3
3
8.4 Hz, P CH and JH-H = 2.0 Hz, NH CH),
6.41 (1H, m, NH), 7.18–7.54 (10H, m, Ar H). IR
(KBr) (νmax cm−1): 3320 (N H), 2969 and 2865
(C Haromatic), 1240 (P O), 1536 and 1347 (N O),
757 (P Caliphatic). Anal. Calcd. for C23H22NO5P: C,
65.24; H, 5.24; N, 3.31; Found: C, 65.19; H, 5.18; N,
3.17.
P-CH and JH-H = 2.0 Hz, NH CH), 6.70 (1H, m,
NH), 7.12–7.55 (11H, m, Ar H). IR (KBr) (νmax
cm−1): 3313 (N H), 2963 and 2864 (C Haromatic),
1236 (P O), 752 (P Caliphatic). EI-MS m/z (%): 413
(10) M+•. Anal. Calcd. for C22H21ClNO3P: C, 63.85;
H, 5.11; N, 3.38; Found: C, 63.78; H, 5.05; N, 3.26.
Dimethyl (((9H-fluoren-2-yl)amino)(2-chlorophe-
Dimethyl
(((9H-fluoren-2-yl)amino)(4-bromo-
nyl) methyl)phosphonate (4f). Pale yellow solid, mp:
phenyl) methyl)phosphonate (4i). Brown solid, mp:
159–161°C. 31P NMR (161.7, MHz, CDCl3) δ: 20.84;
13C NMR (100.56 MHz, CDCl3) δ: 114.4 (C-1), 150.5
(C-2), 108.2 (C-3), 121.7 (C-4), 122.6 (C-5), 127.4
(C-6), 128.5 (C-7), 126.5 (C-8), 37.2 (C-9), 145.4
(C-10), 129.5 (C-11), 138.1 (C-12), 140.4 (C-13), 56.7
(C-15), 135.8 (C-16), 130.8 (C-17 and C-21), 135.1
(C-18 and C-20), 127.2 (C-19), 53.3 (P OCH3), 53.5
(P OCH3); 1H NMR (400 MHz, CDCl3) δ: 3.51 (3H,
168–170°C. 31P NMR (161.89, MHz, CDCl3) δ: 20.72;
3
1H NMR (400 MHz, CDCl3) δ: 3.57 (3H, d, JH-P
=
3
10.4 Hz, P OCH3), 3.78 (3H, d, JH-P = 10.4 Hz,
P
OCH3), 3.67 (2H, s, Ar CH2 Ar), 6.55–6.56 (1H,
2
3
dd, JH-P = 8.4 Hz, P CH and JH-H = 2.0 Hz,
NH CH), 6.70 (1H, m, NH), 7.12–7.55 (11H, m,
Ar H). IR (KBr) (νmax cm−1): 3314 (N H), 2961 and
2865 (C Haromatic), 1231 (P O), 752 (P Caliphatic).
Anal. Calcd. for C22H21ClNO3P: C, 63.85; H, 5.11; N,
3.38; Found: C, 63.79; H, 5.08; N, 3.25.
3
3
d, JH-P = 10.4 Hz, P OCH3), 3.74 (3H, d, JH-P
= 10.4 Hz, P OCH3), 3.66 (2H, s, Ar CH2-Ar),
6.54–6.59 (1H, dd, 2JH-P = 8.4 Hz, P CH and 3JH-H
=
Dimethyl (((9H-fluoren-2-yl)amino)(2,3-dihydro-
benzo[b][1,4]dioxin-6-yl)methyl) phosphonate (4g).
Brown solid, mp: 196–198°C. 31P NMR (161.7, MHz,
CDCl3) δ: 20.36; 13C NMR (100.56 MHz, CDCl3)
δ: 114.1 (C-1), 150.6 (C-2), 109.2 (C-3), 121.5
(C-4), 122.2 (C-5), 128.2 (C-6), 129.4 (C-7), 126.3 (C-
8), 36.8 (C-9), 145.1 (C-10), 129.7 (C-11), 138.8 (C-
12), 141.5 (C-13), 56.2 (C-15), 129.5 (C-16), 116.4
(C-17), 112.8 (C-18), 65.8 (C-20 and C-21), 110.3
(C-23), 151.2 (C-24), 150.8 (C-25), 52.9 (P OCH3),
2.0 Hz, NH CH), 6.67 (1H, m, NH), 7.01–7.45 (11H,
m, Ar H). IR (KBr) (νmax cm−1): 3315 (N H),
2958 and 2860 (C Haromatic), 1238 (P O), 756
(P Caliphatic). Anal. Calcd. for C22H21BrNO3P: C,
57.66; H, 4.62; N, 3.06; Found: C, 57.59; H, 4.58; N,
3.01.
Dimethyl (((9H-fluoren-2-yl)amino)(4-nitrophe-
nyl) methyl)phosphonate (4j) [6]. Yellow solid, mp:
186–188°C. 31P NMR (161.7, MHz, CDCl3) δ: 21.26;
Heteroatom Chemistry DOI 10.1002/hc

8
Gangireddy et al.
3
13C NMR (100.56 MHz, CDCl3) δ: 114.5 (C-1), 150.6
(C-2), 108.1 (C-3), 121.8 (C-4), 122.4 (C-5), 127.6 (C-
6), 128.7 (C-7), 126.3 (C-8), 37.6 (C-9), 145.2 (C-10),
129.6 (C-11), 138.4 (C-12), 140.6 (C-13), 56.9 (C-15),
138.8 (C-16), 128.8 (C-17 and C-21), 126.2 (C-18 and
= 10.4 Hz, P OCH3), 3.76 (3H, d, JH-P = 10.4 Hz,
P
OCH3), 3.68 (2H, s, Ar CH2 Ar), 6.53–6.58 (1H,
2
3
dd, JH-P = 8.4 Hz, P CH and JH-H = 2.0 Hz,
NH CH), 6.79 (1H, m, NH), 7.10–7.54 (11H, m,
Ar H). IR (KBr) (νmax cm−1): 3340 (N H), 2965 and
2862 (C Haromatic), 1248 (P O), 759 (P Caliphatic).
Anal. Calcd. for C22H22NO4P: C, 66.83; H, 5.61; N,
3.54; Found: C, 66.77; H, 5.56; N, 3.47.
C-20), 151.2 (C-19), 52.3 (P OCH3), 53.2 (P OCH3);
3
1H NMR (400 MHz, CDCl3) δ: 3.56 (3H, d, JH-P
=
3
10.4 Hz, P OCH3), 3.76 (3H, d, JH-P = 10.4 Hz,
P
OCH3), 3.76 (2H, s, Ar CH2 Ar), 6.66–6.71 (1H,
2
3
dd, JH-P = 8.4 Hz, P CH and JH-H = 2.0 Hz,
NH CH), 6.69 (1H, m, NH), 7.23–7.75 (11H, m,
Ar H). IR (KBr) (νmax cm−1): 3331 (N H), 2965 and
2862 (C Haromatic), 1261 (P O), 753 (P Caliphatic).
Anal. Calcd. for C22H21N2O5P: C, 62.26; H, 4.99; N,
6.60; Found: C, 62.20; H, 4.93; N, 6.56.
Dimethyl (((9H-fluoren-2-yl)amino) (cyclohexyl)
methyl)phosphonate (4n). Pale yellow solid, mp:
167–169°C. 31P NMR (161.7, MHz, CDCl3) δ: 20.
61; 13C NMR (100.56 MHz, CDCl3) δ: 113.8 (C-
1), 149.8 (C-2), 109.6 (C-3), 121.6 (C-4), 122.8 (C-
5), 127.8 (C-6), 128.3 (C-7), 126.5 (C-8), 36.9 (C-9),
145.9 (C-10), 129.8 (C-11), 138.2 (C-12), 140.5 (C-
13), 53.8 (C-15), 23.4 (C-16), 29.7 (C-17 and 21),
25.9 (C-18 and 20), 26.8 (C-19), 52.7 (P OCH3), 53.5
(P OCH3); 1H NMR (400 MHz, CDCl3) δ: 3.50 (3H,
Dimethyl (((9H-fluoren-2-yl)amino)(2-nitrophe-
nyl) methyl)phosphonate (4k). Yellow solid, mp:
182–184°C. 31P NMR (161.7, MHz, CDCl3) δ: 21.67;
3
3
3
1H NMR (400 MHz, CDCl3) δ: 3.55 (3H, d, JH-P
=
d, JH-P = 10.4 Hz, P OCH3), 3.69 (3H, d, JH-P
= 10.4 Hz, P OCH3), 3.51 (2H, s, Ar CH2 Ar),
3
10.4 Hz, P OCH3), 3.78 (3H, d, JH-P = 10.4 Hz,
2
3
P
OCH3), 3.71 (2H, s, Ar CH2 Ar), 6.65–6.70 (1H,
6.65–6.67 (1H, dd, JH-P = 8.4 Hz, P CH and JH-H
= 2.0 Hz, NH CH), 6.74 (1H, m, NH), 7.08–7.75
(7H, m, Ar H), 1.35–1.53 (12H, m, C Hcyclohexane).
IR (KBr) (νmax cm−1): 3339 (N-H), 2966 and 2865
(C Haromatic), 1230 (P O), 759 (P Caliphatic). EI-MS
m/z (%): 385 (11) M+•. Anal. Calcd. for C22H28NO3P:
C, 68.55; H, 7.32; N, 3.63; Found: C, 68.47; H, 7.28;
N, 3.58.
2
3
dd, JH-P = 8.4 Hz, P CH and JH-H = 2.0 Hz,
NH CH), 6.53 (1H, m, NH), 7.30–7.78 (11H, m,
Ar H). IR (KBr) (νmax cm−1): 3329 (N H), 2965 and
2861 (C Haromatic), 1262 (P O), 755 (P Caliphatic).
EI-MS m/z (%): 424 (5) M+•. Anal. Calcd. for
C22H21N2O5P: C, 62.26; H, 4.99; N, 6.60; Found: C,
62.21; H, 4.93; N, 6.52.
Dimethyl (((9H-fluoren-2-yl)amino)(4-hydroxy-
phenyl) methyl)phosphonate (4l). Brown solid, mp:
192–194°C. 31P NMR (161.7, MHz, CDCl3) δ: 22.01;
13C NMR (100.56 MHz, CDCl3) δ: 114.8 (C-1), 150.9
(C-2), 108.6 (C-3), 121.5 (C-4), 122.4 (C-5), 127.9
(C-6), 128.8 (C-7), 126.8 (C-8), 37.6 (C-9), 145.2 (C-
10), 129.8 (C-11), 138.8 (C-12), 140.3 (C-13), 56.9
(C-15), 130.9 (C-16), 129.9 (C-17 and C-21), 115.2
(C-18 and C-20), 161.7 (C-19), 52.8 (P OCH3), 53.5
(P OCH3); 1H NMR (400 MHz, CDCl3) δ: 3.58 (3H,
Dimethyl (1-((9H-fluoren-2-yl)amino) propyl)-
phosphonate (4o) [6]. Brown solid, mp: 128–130°C.
31P NMR (161.7, MHz, CDCl3) δ: 20.59; 1H NMR
3
(400 MHz, CDCl3) δ: 3.55 (3H, d, JH-P = 10.4 Hz,
3
P
OCH3), 3.71 (3H, d, JH-P = 10.4 Hz, P OCH3),
3.58 (2H, s, Ar CH2 Ar), 6.63–6.65 (1H, dd, 2JH-P
=
8.4 Hz, P-CH and 3JH-H = 2.0 Hz, NH CH), 5.87 (1H,
m, NH), 7.07–7.63 (7H, m, Ar H), 1.35–1.43 (2H, m,
CH2), 1.08 (3H, t, CH3). IR (KBr) (νmax cm−1): 3309
(N H), 2960 and 2857 (C Haromatic), 1242 (P O),
759 (P Caliphatic). EI-MS m/z (%): 331 (10) M+•. Anal.
Calcd. for C18H22NO3P: C, 65.25; H, 6.69; N, 4.23;
Found: C, 65.19; H, 6.62; N, 4.18.
3
3
d, JH-P = 10.4 Hz, P OCH3), 3.78 (3H, d, JH-P
= 10.4 Hz, P OCH3), 3.69 (2H, s, Ar CH2 Ar),
2
6.54–6.59 (1H, dd, JH-P = 8.4 Hz, P CH and
3JH-H = 2.0 Hz, NH CH), 6.77 (1H, m, NH), 7.11–
7.53 (11H, m, Ar H). IR (KBr) (νmax cm−1): 3329
(N H), 2960 and 2858 (C Haromatic), 1260 (P O),
751 (P Caliphatic). EI-MS m/z (%): 395 (9) M+•. Anal.
Calcd. for C22H22NO4P: C, 66.83; H, 5.61; N, 3.54;
Found: C, 66.79; H, 5.58; N, 3.48.
Dimethyl (1-((9H-fluoren-2-yl)amino) butyl)-
phosphonate (4p). Brown solid, mp: 134–136°C.
31P NMR (161.7, MHz, CDCl3) δ: 21.11; 1H NMR
3
(400 MHz, CDCl3) δ: 3.52 (3H, d, JH-P = 10.4 Hz,
3
P
OCH3), 3.73 (3H, d, JH-P = 10.4 Hz, P OCH3),
3.56 (2H, s, Ar CH2 Ar), 6.61–6.65 (1H, dd, 2JH-P
=
3
Dimethyl (((9H-fluoren-2-yl)amino)(3-hydroxy-
phenyl) methyl)phosphonate (4m). Brown solid,
mp: 191–193°C. 31P NMR (161.7, MHz, CDCl3) δ:
21.79; 1H NMR (400 MHz, CDCl3) δ: 3.58 (3H, d, 3JH-P
8.4 Hz, P CH and JH-H = 2.0 Hz, NH CH), 5.85
(1H, m, NH), 7.11–7.62 (7H, m, Ar H), 1.31–1.45
(4H, m, 2 × CH2), 1.08 (3H, t, CH3). IR (KBr) (νmax
cm−1): 3311 (N H), 2968 and 2866 (C Haromatic),
Heteroatom Chemistry DOI 10.1002/hc

Synthesis of α-Aminophosphonates under Microwave Irradiation Conditions in the Presence of PS/PTSA
9
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1254 (P O), 762 (P Caliphatic). EI-MS m/z (%): 345
(5) M+•. Anal. Calcd. for C19H24NO3P: C, 66.07; H,
7.00; N, 4.06; Found: C, 66.01; H, 6.96; N, 4.02.
[4] Janardhan Rao, A.; Visweswara Rao, P.; Koteswara
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Dimethyl (1-((9H-fluoren-2-yl)amino)-3-methyl-
butyl) phosphonate (4q). Pale yellow solid, mp:
137–139°C. 31P NMR (161.7, MHz, CDCl3) δ: 21.59;
3
1H NMR (400 MHz, CDCl3) δ: 3.52 (3H, d, JH-P
=
3
10.4 Hz, P OCH3), 3.70 (3H, d, JH-P = 10.4 Hz,
P
OCH3), 3.54 (2H, s, Ar CH2 Ar), 6.66–6.69 (1H,
2
3
dd, JH-P = 8.4 Hz, P-CH and JH-H = 2.0 Hz, NH-
CH), 5.85 (1H, m, NH), 7.13–7.63 (7H, m, Ar H),
1.36–1.48 (2H, m, CH2), 1.59 (1H, m, CH), 1.04
(6H, d, (CH3)2). IR (KBr) (νmax cm−1): 3314 (N H),
2964 and 2862 (C Haromatic), 1248 (P O), 760 (P-
Caliphatic). EI-MS m/z (%): 359 (8) M+•. Anal. Calcd.
for C20H26NO3P: C, 66.84; H, 7.29; N, 3.90; Found:
C, 66.78; H, 7.23; N, 3.84.
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Wadgaonkar, P. P. Catal Commun 2008, 9, 1822–
1826.
Dimethyl (1-((9H-fluoren-2-yl)amino) pentyl)-
phosphonate (4r). Pale yellow solid, mp: 141–
143°C. 31P NMR (161.7, MHz, CDCl3) δ: 21.10; 13C
NMR (100.56 MHz, CDCl3) δ: 113.6 (C-1), 149.5 (C-
2), 109.4 (C-3), 121.5 (C-4), 122.7 (C-5), 127.6 (C-
6), 128.4 (C-7), 126.5 (C-8), 36.7 (C-9), 145.6 (C-10),
129.4 (C-11), 138.1 (C-12), 140.4 (C-13), 53.7 (C-15),
22.3 (C-16), 29.1 (C-17), 23.2 (C-18), 15.8 (C-19), 52.2
(P OCH3), 53.1 (P OCH3); 1H NMR (400 MHz,
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SSSR 1952, 83, 689.
3
CDCl3) δ: 3.54 (3H, d, JH-P = 10.4 Hz, P OCH3),
3
3.76 (3H, d, JH-P = 10.4 Hz, P OCH3), 3.58 (2H,
2
s, Ar CH2 Ar), 6.63–6.66 (1H, dd, JH-P = 8.4 Hz,
3
P-CH and JH-H = 2.0 Hz, NH CH), 5.89 (1H, m,
[19] Kabachnik, M. I.; Medved, T. Ya. Izv Akad Nauk
SSSR, Ser Chim 1953, 1126.
NH), 7.13–7.61 (7H, m, Ar H), 1.23–1.52 (6H, m, 3
× CH2), 1.01 (3H, t, CH3). IR (KBr) (νmax cm−1): 3319
(N H), 2963 and 2862 (C Haromatic), 1252 (P O),
764 (P Caliphatic). Anal. Calcd. for C20H26NO3P: C,
66.84; H, 7.29; N, 3.90; Found: C, 66.76; H, 7.21; N,
3.83.
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ACKNOWLEDGMENTS
The authors express their grateful thanks to Prof.
C. Suresh Reddy, Department of Chemistry, Sri
Venkateswara University, Tirupati, India, for his
helpful discussions.
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Heteroatom Chemistry DOI 10.1002/hc