TMSCI-promoted addition of diethyl phosphite to an imine for the synthesis of bis[1-diethoxyphosphorylalkyl]amines

Article abstract of DOI:10.1055/s-2006-942432

A convenient preparative approach for the synthesis of bis[1- diethoxyphosphorylalkyl]amines has been developed. Treatment of aromatic aldehydes with ammonia and reaction with diethyl phosphite gives diethyl aryl[(arylmethylidene)amino]methylphosphonates,

Full text of DOI:10.1055/s-2006-942432

PAPER
2339
TMSCl-Promoted Addition of Diethyl Phosphite to an Imine for the Synthesis
of Bis[1-diethoxyphosphorylalkyl]amines
S
ynthesis of Bis[
a
b
hosphoryla
l
a
kyl]aminesk Kaboudin,* Khavar Moradi
Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Gava Zang, Zanjan 45195-1159, Iran
Fax +98(241)4249023; E-mail: kaboudin@iasbs.ac.ir
Received 10 February 2006; revised 14 March 2006
alkyl] amines in the reaction of 1-iminocarboxylate salts
Abstract: A convenient preparative approach for the synthesis of
with dialkyl chlorophosphites has been reported.17 How-
ever, these methods have drawbacks, including harsh re-
action conditions, long reaction times, and side reactions.
bis[1-diethoxyphosphorylalkyl]amines has been developed. Treat-
ment of aromatic aldehydes with ammonia and reaction with diethyl
phosphite gives diethyl aryl[(arylmethylidene)amino]methylphos-
phonates, which can be easily reacted with diethyl phosphite in the On the other hand, prolonged heating of chlorometh-
presence of chlorotrimethylsilane to give bis[1-diethoxyphosphor-
ylphosphonic acids in alkaline solution also leads to the
ylalkyl]amines. This method is easy, rapid, and good-yielding for
competitive hydrolysis product of the chlorine–carbon
the synthesis of bis[1-diethoxyphosphorylalkyl]amines from simple
bond to give hydroxymethylphosphonic acid.15 As a part
starting materials.
of our efforts to introduce novel methods for the synthesis
of organophosphorus compounds,18 we present here a new
Key words: TMSCl, diethyl phosphite, imines, bis[1-diethoxy-
phosphorylalkyl]amines, addition reaction
method for the synthesis of bis[1-diethoxyphosphoryl-
alkyl]amines is described. Recently, we reported that re-
action of aromatic aldehydes with ammonia solution
followed by reaction with diethyl phosphite, gave diethyl
Organophosphorus compounds have found a wide range
of applications in the areas of industrial, agricultural, and
aryl[(arylmethylidene)amino]methylphosphonates
in
medicinal chemistry owing to their biological and physi-
cal properties as well as their use as synthetic intermedi-
ates.1 a-Functionalized phosphonic acids are valuable
intermediates for the preparation of medicinal compounds
and synthetic intermediates.2–4 Among the a-functional
phosphonic acids, 1-aminophosphonic acids are an impor-
tant class of compounds that exhibit a variety of interest-
ing and useful properties. 1-Aminophosphonic acids are
important substitutes for the corresponding a-amino acids
in biological systems.5 Indeed a number of potent antibi-
otics,6 enzyme inhibitors,7 and pharmacological agents8
are 1-aminophosphonic acids or peptide analogues. Ami-
nophosphonic acids are also found as constituents of nat-
ural products.9 In contrast to the widely studied 1-
aminophosphonic acids derivatives,10–13 relatively few pa-
pers have reported on the chemistry of bis[1-diethoxy-
phosphorylalkyl]amines as an important class of 1-
aminophosphonic acid derivatives. Bis[1-dialkoxyphos-
phorylalkyl]amines have been used as chelating agents for
polyvalent, particularly for alkaline earth metal ions.14
good yields that can be easily hydrolyzed to diethyl
1-aminoarylmethylphosphonates.19 We have now found
that the reaction of diethyl phenyl[(phenylmethyl-
idene)amino]methylphosphonate (1a), as a model com-
pound, with diethyl phosphite in the presence of
chlorotrimethylsilane (0.5 equiv) gives bis[1-diethoxy-
phosphorylphenylmethyl]amine (2a) as sole product
(Scheme 1). The reaction can be carried out in 0.2 equiv-
alent of chlorotrimethylsilane involving a long reaction
period (12 h). The reaction failed even after 48 hours
when carried out without any catalyst. Use of other Lewis
acid catalysts such as AlCl3, FeCl3, TiCl4, LiClO4 and
ZnCl2 did not give any product.
The 31P NMR spectrum of 2a exhibited two peaks at d =
22.78 and 23.08 due to diastereoisomers. An excellent
diastereoselection can be obtained in this reaction (93:7).
O
1) NH4OH(aq)
H
PhCHO
Ph
P(OEt)2
C
2) diethyl phosphite
N
Many effective methods for the preparation of 1-amino-
phosphonic acids have been developed, but, to the best of
our knowledge, few synthetic routes to bis[1-diethoxy-
phosphorylalkyl]amines have been reported. These meth-
ods involve prolonged heating of primary amines with
chloromethylphosphonic acids in alkaline solution15and a
Mannich-type reaction of an amine, formaldehyde, and
phosphorous acid is also reported.16 Recently, a new
method for the preparation of bis[1-diethoxyphosphoryl-
CH
Ph
1a
1) diethyl phosphite
2) TMSCl (0.5 equiv)
CH2Cl2, 3 h, r.t.
Ph
H
H
H
H
Ph
Ph
Ph
(EtO)2(O)P
N
H
P(O)(OEt)2
(EtO)2(O)P
N
H
P(O)(OEt)2
SYNTHESIS 2006, No. 14, pp 2339–2342
Advanced online publication: 26.06.2006
x
x.
x
x
.
2
0
0
6
syn-2a
anti-2a
Scheme 1
DOI: 10.1055/s-2006-942432; Art ID: Z03306SS
© Georg Thieme Verlag Stuttgart · New York

2340
B. Kaboudin, K. Moradi
PAPER
Table 1 Reaction of 1 with Diethyl Phosphite Using Chlorotrimethylsilane as Catalyst
Entry
R
Time (h)
Yield of 2 (%)a
Diastereoselection (%)b 31P NMR, d
Major
Minor
a
b
c
d
e
f
Ph
3
5
2
2
2
5
3
2
5
3
5
78
80
65
73
76
65
73
70
70
73
63
93: 7
22.78
23.21
22.03
21.83
22.36
23.21
22.78
21.52
22.93
21.71
22.75
23.08
23.44
22.40
22.20
22.68
23.48
22.99
21.98
23.22
22.17
23.09
4-MeOCHC6H4
4-ClC6H4
4-BrC6H4
4-FC6H4
81:19
94: 6
84:16
88:12
73:27
84:16
87:13
79:21
89:11
89:11
4-MeC6H4
3-MeOCHC6H4
3-BrC6H4
3-MeC6H4
3-FC6H4
g
h
i
j
k
b-Naphthyl
a Isolated yield.
b Diastereoselection was calculated from 31P NMR spectra.
Due to the presence of two stereogenic carbons bonded to tions with no tar formation make this method an attractive
the nitrogen atom, this compound exists as two diastereo- and useful contribution to present methodologies. Indeed,
meric forms: one meso (syn) and one racemic pair (anti).
a wide range of imines 1 was converted into the corre-
sponding bis[1-diethoxyphosphorylalkyl]amines using
this method. Further investigations on this reaction are
now in progress.
This process was successfully applied to other diethyl ar-
yl[(arylmethylidene)amino]methylphosphonates 1b–k as
summarized in Table 1. Methylphosphonates 1b–k19 react
with diethyl phosphite in the presence of chlorotrimethyl-
silane to afford the desired products 2b–k in good yields.
The mechanism of formation of 2 is illustrated in
Scheme 2. Reaction between ammonium hydroxide and
aliphatic aldehydes failed with diethyl phosphite and did
not give any imines 1.
All chemicals were commercial products and distilled or recrystal-
lized before use. All melting points were obtained on a Büchi 510
melting point apparatus and are uncorrected. The IR spectra were
determined using a FT-IR Bruker-Vector 22 spectrophotometer.
NMR spectra were taken with a 250 Bruker Avance instrument with
the chemical shifts being reported as d in ppm and coupling con-
stants expressed in Hz. Silica gel column chromatography was car-
ried out with silica gel 100 (Merck No. 10184). Merck silica gel 60
F254 plates (No. 5744) were used for the preparative TLC.
In summary, fast reaction rates, mild reaction conditions,
good yields, simple work-up, and relatively clean reac-
O
H
Imines 1; General Procedure
R
P(OEt)2
C
The aldehyde (15 mmol) was added to NH4OH (30%, 15 mL) and
the solution was stirred for 5 h at reflux. During this time, a white
precipitate formed. The precipitate was removed by filtration and
dried. Diethyl phosphite (828 mg, 6 mmol) was added to this solid
and the resulting solution was stirred for 2–5 h at 70 °C. Chroma-
tography on silica gel with EtOAc–n-hexane (5:5) gave the pure
products 1 as oils.19
N
Me
Me Si Cl
Me
O
R
R O
CH
R
(EtO)2P CH
CH P(OEt)2
N
H
1
2
Bis[1-diethoxyphosphorylalkyl]amines 2; General Procedure
Chlorotrimethylsilane (217 mg, 2 mmol) was added to compound 1
(4 mmol) in CH2Cl2 (20 mL) and the mixture was stirred for 2–5 h
at r.t. The solvent was evaporated and the residue was chromato-
graphed on a plug of silica gel using EtOAc–MeOH (9:1) as eluent.
Evaporation of the solvent under reduced pressure gave the pure
product as colorless oil in 63–80% yields. All products gave satis-
factory spectral data in accord with the assigned structures.
O
H
C
O
R
R O
R
P(OEt)2
(EtO)2P CH CH P(OEt)2
N
Cl
N
Me3Si
CH
R
Me3Si
H
Cl
O
Bis(1-diethoxyphosphorylphenylmethyl)amine (2a)
H
P(OEt)2
Colorless oil; yield: 78%.
Scheme 2
Synthesis 2006, No. 14, 2339–2342 © Thieme Stuttgart · New York

PAPER
Synthesis of Bis[1-diethoxyphosphorylalkyl]amines
2341
1H NMR (CDCl3/TMS, 250 MHz): d = 1.10 (6 H, t, J = 7.1 Hz),
1.26 (6 H, t, J = 7.1 Hz), 2.93 (1 H, br, NH), 3.65–4.35 (10 H, m),
7.29 (10 H, s).
13C NMR (CDCl3/TMS, 62.9 MHz): d = 134.3, 128.8, 128.2, 128.1,
62.6–62.9 (OCH2CH3), 57.4 (dd, JP,C = 155.1, 17.9 Hz), 16.1–16.3
(OCH2CH3).
Bis[1-diethoxyphosphoryl(4-methylphenyl)methyl]amine (2f)
Colorless oil; yield: 65%.
1H NMR (CDCl3/TMS, 250 MHz): d = 1.04 (6 H, t, J = 7.1 Hz),
1.19 (6 H, t, J = 7.1 Hz), 2.24 (3 H, s), 2.85 (1 H, br, NH), 3.60–4.25
(10 H, m), 6.95–7.15 (8 H, m).
13C NMR (CDCl3/TMS, 62.9 MHz): d = 137.7, 131.1, 129.2, 128.7,
62.4–62.9 (OCH2CH3), 57.0 (dd, JP,C = 156.0, 18.2 Hz), 21.1, 16.1–
16.3 (OCH2CH3).
31P NMR (CDCl3/H3PO4): d = 22.78, 23.08 (93:7).
Anal. Calcd for C22H33NO6P2: C, 56.29; H, 7.08; N, 2.98. Found: C,
56.20; H, 7.10; N, 2.78.
31P NMR (CDCl3/H3PO4): d = 23.21, 23.48 (73:27).
Anal. Calcd for C24H37NO6P2: C, 61.93; H, 7.95; N, 3.01. Found: C,
61.75; H, 7.79; N, 2.92.
Bis[1-diethoxyphosphoryl(4-methoxyphenyl)methyl]amine
(2b)
Colorless oil; yield: 80%.
Bis[1-Diethoxyphosphoryl(3-methoxyphenyl)methyl]amine
(2g)
Colorless oil; yield: 73%.
1H NMR (CDCl3/TMS, 250 MHz): d = 1.08 (6 H, t, J = 7.1 Hz),
1.22 (6 H, t, J = 7.1 Hz), 2.78 (1 H, br, NH), 3.72 (3 H, s), 3.64–4.23
(10 H, m), 6.70–6.87 (4 H, m), 7.08–7.21 (4 H, m).
13C NMR (CDCl3/TMS, 62.9 MHz): d = 159.7, 135.9, 129.9, 125.4,
114.0, 62.7–63.0 (OCH2CH3), 57.3 (dd, JP,C = 155.0, 17.9 Hz),
55.1, 16.1–16.4 (OCH2CH3).
1H NMR (CDCl3/TMS, 250 MHz): d = 1.14 (6 H, t, J = 7.1 Hz),
1.29 (6 H, t, J = 7.1 Hz), 1.69 (1 H, br, NH), 3.79 (3 H, s), 3.68–4.35
(10 H, m), 6.87 (4 H, d, J = 8.5 Hz), 7.22 (4 H, d, J = 8.5 Hz).
13C NMR (CDCl3/TMS, 62.9 MHz): d = 159.4, 129.9, 125.9, 113.8,
62.4–62.8 (OCH2CH3), 56.4 (dd, JP,C = 156.7, 17.9 Hz), 55.1, 16.1–
16.3 (OCH2CH3).
31P NMR (CDCl3/H3PO4): d = 23.21, 23.44 (81:19).
Anal. Calcd for C24H37NO8P2: C, 54.44; H, 6.99; N, 2.65. Found: C,
54.32; H, 7.08; N, 2.73.
31P NMR (CDCl3/H3PO4): d = 22.78, 22.99 (84:16).
Anal. Calcd for C24H37NO8P2: C, 54.44; H, 6.99; N, 2.65. Found: C,
54.60; H, 7.10; N, 2.81.
Bis[1-diethoxyphosphoryl(4-chlorophenyl)methyl]amine (2c)
Colorless oil; yield: 65%.
1H NMR (CDCl3/TMS, 250 MHz): d = 1.15 (6 H, t, J = 7.1 Hz),
1.29 (6 H, t, J = 7.1 Hz), 2.19 (1 H, br, NH), 3.65–4.35 (10 H, m),
7.23 (4 H, d, J = 8.25 Hz), 7.33 (4 H, d, J = 8.25 Hz).
13C NMR (CDCl3/TMS, 62.9 MHz): d = 134.1, 132.9, 130.1, 128.9,
62.9–63.2 (OCH2CH3), 56.9 (dd, JP,C = 155.4, 17.6 Hz), 16.3–16.4
(OCH2CH3).
Bis[1-diethoxyphosphoryl(3-bromophenyl)methyl]amine (2h)
Colorless oil; yield: 70%.
1H NMR (CDCl3/TMS, 250 MHz): d = 1.01–1.29 (12 H, m), 1.52
(1 H, br, NH), 3.55–4.20 (10 H, m), 7.06–7.48 (10 H, s).
13C NMR (CDCl3/TMS, 62.9 MHz): d = 136.8, 131.5, 131.4, 130.1,
127.5, 122.7, 62.9–63.3 (OCH2CH3), 57.1 (dd, JP,C = 155.1, 17.9
Hz), 16.2–16.3 (OCH2CH3).
31P NMR (CDCl3/H3PO4): d = 22.03, 22.40 (94:6).
Anal. Calcd for C22H31Cl2NO6P2: C, 52.17; H, 6.12; N, 2.76. Found:
C, 52.30; H, 5.98; N, 2.65.
31P NMR (CDCl3/H3PO4): d = 21.52, 21.98 (87:13).
Anal. Calcd for C22H31Br2NO6P2: C, 44.38; H, 5.21; N, 2.35. Found:
C, 44.51; H, 5.35; N, 2.48.
Bis[1-diethoxyphosphoryl(4-bromophenyl)methyl]amine (2d)
Colorless oil; yield: 73%.
Bis[1-diethoxyphosphoryl(3-methylphenyl)methyl]amine (2i)
Colorless oil; yield: 70%.
1H NMR (CDCl3/TMS, 250 MHz): d = 1.15 (6 H, t, J = 7.1 Hz),
1.29 (6 H, t, J = 7.1 Hz), 2.45 (1 H, br, NH), 3.72 (2 H, d, JP,C = 22
Hz), 3.75–4.25 (8 H, m), 7.17 (4 H, dd, J = 8.25, 1.5 Hz), 7.47 (4 H,
d, J = 8.25 Hz).
13C NMR (CDCl3/TMS, 62.9 MHz): d = 133.5, 131.8, 130.5, 122.3,
62.9–63.2 (OCH2CH3), 56.9 (dd, JP,C = 155.4, 17.6 Hz), 16.2–16.4
(OCH2CH3).
1H NMR (CDCl3/TMS, 250 MHz): d = 1.00 (6 H, t, J = 7.0 Hz),
1.17 (6 H, t, J = 7.0 Hz), 2.21 (3 H, s), 2.82 (1 H, br, NH), 3.63–4.20
(10 H, m), 6.97–7.13 (8 H, m).
13C NMR (CDCl3/TMS, 62.9 MHz): d = 137.9, 134.2, 129.2, 128.8,
128.2, 126.0, 62.2–62.8 (OCH2CH3), 57.3 (dd, JP,C = 154.9, 17.9
Hz), 21.3, 16.0–16.3 (OCH2CH3).
31P NMR (CDCl3/H3PO4): d = 21.83, 22.20 (84:16).
31P NMR (CDCl3/H3PO4): d = 22.93, 23.22 (79:21).
Anal. Calcd for C22H31Br2NO6P2: C, 44.38; H, 5.21; N, 2.35. Found:
C, 44.40; H, 5.32; N, 2.25.
Anal. Calcd for C24H37NO6P2: C, 61.93; H, 7.95; N, 3.01. Found: C,
61.82; H, 7.83; N, 2.89.
Bis[1-diethoxyphosphoryl(4-fluorophenyl)methyl]amine (2e)
Colorless oil; yield: 76%.
Bis[1-diethoxyphosphoryl(3-fluorophenyl)methyl]amine (2j)
Colorless oil; yield: 73%.
1H NMR (CDCl3/TMS, 250 MHz): d = 1.04 (6 H, t, J = 7.0 Hz),
1.18 (6 H, t, J = 7.0 Hz), 2.82 (1 H, br, NH), 3.57–4.22 (10 H, m),
6.80–6.97 (4 H, m), 7.10–7.22 (4 H, m).
13C NMR (CDCl3/TMS, 62.9 MHz): d = 162.0 (d, JC,F = 246.5 Hz),
130.4, 115.7, 115.3, 62.6–63.0 (OCH2CH3), 56.6 (dd, JP,C = 156.6,
17.6 Hz), 16.1–16.3 (OCH2CH3).
1H NMR (CDCl3/TMS, 250 MHz): d = 1.11 (6 H, t, J = 7.0 Hz),
1.24 (6 H, t, J = 7.0 Hz), 2.92 (1 H, br, NH), 3.65–4.25 (10 H, m),
6.85–7.09 (6 H, m), 7.15–7.32 (2 H, m).
13C NMR (CDCl3/TMS, 62.9 MHz): d = 162.9 (d, JC,F = 246.8 Hz),
137.1, 130.1, 124.5, 115.7, 115.3, 62.9–63.2 (OCH2CH3), 57.2 (dd,
JP,C = 155.1, 17.4 Hz), 16.1–16.3 (OCH2CH3).
31P NMR (CDCl3/H3PO4): d = 22.36, 22.68 (88:12).
31P NMR (CDCl3/H3PO4): d = 21.71, 22.17 (89:11).
Anal. Calcd for C22H31F2NO6P2: C, 55.81; H, 6.55; N, 2.96. Found:
C, 55.72; H, 6.50; N, 3.15.
Anal. Calcd for C22H31F2NO6P2: C, 55.81; H, 6.55; N, 2.96. Found:
C, 55.68; H, 6.42; N, 3.10.
Synthesis 2006, No. 14, 2339–2342 © Thieme Stuttgart · New York

2342
B. Kaboudin, K. Moradi
PAPER
(6) Atherton, F. R.; Hassal, C. H.; Lambert, R. W. J. Med.
Bis[1-diethoxyphosphoryl(b-naphthyl)methyl]amine (2k)
Colorless oil; yield: 63%.
Chem. 1987, 30, 1603.
(7) Allen, M. C.; Fuhrer, W.; Tuck, B.; Wade, R.; Wood, J. M.
J. Med. Chem. 1989, 32, 1652.
(8) Hassal, C. H. In Antibiotics, Vol VI; Hahn, F. E., Ed.;
Springer Verlag: Berlin, 1983, 1–11.
(9) Kukhar, V. P.; Hudson, H. R. Aminophosphonic and
Aminophosphinic Acids; Wiley: Chichester, 2000.
(10) Hyun-Joon, H.; Gong-Sil, N. Synth. Commun. 1992, 22,
1143.
(11) Gancarz, R.; Wieczorek, J. S. Synthesis 1978, 625.
(12) Seyferth, D.; Marmor, R. S.; Hilbert, P. J. Org. Chem. 1971,
36, 1379.
1H NMR (CDCl3/TMS, 250 MHz): d = 1.10 (6 H, t, J = 7.0 Hz),
1.31 (6 H, t, J = 7.0 Hz), 3.03 (1 H, br, NH), 3.70–4.57 (10 H, m),
7.35–7.92 (14 H, m).
13C NMR (CDCl3/TMS, 62.9 MHz): d = 133.3, 132.0, 131.9, 128.4,
127.9, 127.7, 126.2, 62.8–63.1 (OCH2CH3), 57.7 (dd, JP,C = 155.1,
17.8 Hz), 16.1–16.3 (OCH2CH3).
31P NMR (CDCl3/H3PO4): d = 22.75, 23.09 (89:11).
Anal. Calcd for C30H37NO6P2: C, 67.04; H, 6.89; N, 2.61. Found: C,
66.88; H, 6.78; N, 2.49.
(13) Worms, K. H.; Schmidt-Dunker, M. In Organic Phosphorus
Compounds, Vol. 7; Kosolapoff, G. M.; Maier, L., Eds.;
Wiley: New York, 1976, 1.
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Acknowledgment
The Institute for Advanced Studies in Basic Sciences (IASBS) is
thanked for supporting this work.
(15) Schwarzenbach, G.; Ackermann, H.; Ruckstuhl, P. Helv.
Chim. Acta 1944, 32, 1175.
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Synthesis 2006, No. 14, 2339–2342 © Thieme Stuttgart · New York