Synthesis and characterization of new ca-disubstituted (diarylaminomethyl)phosphonates

Article abstract of DOI:10.1055/s-1998-2125

A convenient and efficient three-step procedure for the preparation of W-protected or unprotected C-disubstituted (di-arylaminomethyOphosphonates 1 is reported. This method allows diversification of the substituents on the carbon in the a-position to the phosphorus, as well as the protective group on the amine and the phosphonate ester group.

Full text of DOI:10.1055/s-1998-2125

SYNTHESIS
August 1998
1167
Synthesis and Characterization of New Cα,α-Disubstituted (Diarylaminomethyl)-
phosphonates
Henri-Jean Cristau,* Jean-Marc Lambert, Jean-Luc Pirat*
Laboratoire de Chimie Organique, E.S.A. 5076 du C.N.R.S., Ecole Nationale Supérieure de Chimie de Montpellier 8, Rue de l’Ecole Normale,
F-34296 Montpellier Cedex 5, France
Fax +33(4)67144319; E-mail: pirat@cit.enscm.fr
Received 28 October 1997; revised 23 December 1997
Abstract: A convenient and efficient three-step procedure for the
preparation of N-protected or unprotected Cα,α-disubstituted (di-
arylaminomethyl)phosphonates 1 is reported. This method allows
compound 4b (R' = 2-tolyl) the ratio Z/E is 40:60. The E
diversification of the substituents on the carbon in the α-position
to the phosphorus, as well as the protective group on the amine
and the phosphonate ester group.
(Ph- and Ar-) are different, two isomers E and Z can be
characterized by NMR and GC/MS; for example, with
isomer is the major product, likely for steric reasons.
The second step is the protection of the amine function with
different groups leading to compounds 5. These protective
groups can be released from Cα,α-disubstituted (aminome-
thyl)phosphonates by basic and/or acidic conditions. This
could be crucial for the biological activity of the Cα,α-di-
substituted (aminomethyl)phosphonates and in particular
for the stability of these compounds in biological media.
Further, the benzyloxycarbonyl protective group can be
specifically cleaved by hydrogenolysis, for synthetic pur-
pose. The yields obtained for this protection step are be-
tween 41 and 95%.
Key words: Cα,α-disubstituted (diarylaminomethyl)phosphon-
ates, Arbuzov reaction, Kabachnik–Fields reaction, imine acyla-
tion
Over the past three decades, several research projects
have been directed toward the synthesis of α-aminophos-
phonic acids 2 and their esters, analogs of amino acids, to
find new biologically active molecules. These compounds
did indeed show enzyme inhibition, antibacterial, antitu-
moral, herbicidal and fungicidal activities.1–15
Recently, C. Toniolo16 reported “the explosive interest in
the study of Cα,α-disubstituted amino acids” 3. These
compounds ‘peptaibols’ are used as proteolytic enzyme
inhibitors and exhibit several attractive biological activi-
ties, for example, against epilepsy.
The last step of the synthesis is an extension of the reactiv-
ity of phosphonate anions on imino electrophiles. This step
gives 1 with good yields, between 35 and 96%. The N-pro-
tected Cα,α-disubstituted (aminomethyl)phosphonates have
1
been characterized unambiguously by IR, 31P, H, 13C
For these reasons, we decided to develop a convenient and
efficient method for the preparation of Cα,α-disubstituted
(aminomethyl)phosphonates 1, another class of new less
well-known compounds.
NMR spectra, elemental analyses and mass spectrometry.
The results are presented in Table 1. One of the com-
pounds 1g, characteristic of this (aminomethyl)phosphon-
ate family, has been analyzed by X-ray diffraction (Fig-
ure). A dimer, i.e. structure, induced by intermolecular
The procedure used for the synthesis of 1 is a generaliza-
tion of the Kabachnik–Fields method described in the lit-
erature.17 This method, in three steps, leads to 1 with good
yields (Scheme).
Scheme
The first step is the preparation of the imines 4, by reacting
arylmagnesium bromide with benzonitrile. The yields ob-
tained are between 60 and 98%. When the substituents
Figure. Dimer structure of compound 1g

SYNTHESIS
Papers
Table 1. Characteristics of the New Cα,α-Disubstituted (Aminomethyl)phosphonates 1
1168
Entry Ar
Y
R′′
Yield (%)
(3 steps)
mp (°C)
(Solvent)
Molecular Formulaa and MS
(matrix)
1a
1b
1c
1d
1e
1f
1g
6b
1h
Ph
o-tolyl
1-naphthyl PhC(O)
Ph
Ph
Ph
Ph
Ph
Ph
PhC(O)
PhC(O)
Et
Et
Et
Et
Et
60, 85, 85
52, 41, 75
98, 95, 90
77, 85, 60
60, 54, 35
60, 41, 52
60, 81, 96
60, 86, 81
60, 81, 85
111–113 (heptane)
95 (heptane)
172–173 (heptane)
103–104 (heptane)
149–150 (heptane)
112–114 (heptane)
185–187 (MeOH/heptane) C24H28NO5PS, FAB+: (NBA) M + H = 474
125–127 (heptane)
129–130 (heptane)
C24H26NO4P, EI: M + H = 424
C25H28NO4P, EI: M + H = 438
C28H28NO4P, FAB+ : (NBA) M + H = 474
C25H28NO4P, FAB+ : (NBA) M + H = 438
C19H24NO4P, FAB+: (NBA) M + H = 362
C25H28NO5P, FAB+: (NBA) M + H = 454
o-tolylC(O)
MeC(O)
PhCH2OC(O) Et
Ts
Et
Et
CH2Ph
Ph2P(O)b
PhC(O)
C29H31NO4P2, FAB+: (GT) M + H = 520
C34H30NO4P, FAB+: (NBA) M + H = 548
a
For all compounds, the elemental microanalytical data are satisfactory: C ± 0.35; H ± 0.27; N ± 0.38; O ± 0.37.
This compound (the starting compound 5i is obtained from the protection of compound 4 by chlorodiphenylphosphine oxide) is an isomer of
the expected compound: surprisingly the phosphonate anion reacts on the nitrogen and not on the carbon atom (the structure has been proved
by 13C NMR and by hydrogenolysis affording diphenylmethane and diphosphorylated amine).
b
anhyd MeOH (12 mL) was added dropwise, the precipitate was fil-
hydrogen bonding, can be observed: no significant in-
tramolecular hydrogen bonds can be seen.
tered and the filtrate concentrated. The crude oil was distilled under
vacuum [bp: 4a 111°C; 4b 127°C/0.4 Torr]. A white colorless oil
(yield: 50–98%) was isolated in a Schlenk tube and characterized by
GC/MS.
Deprotection studies were performed on three compounds
1a, 1f and 1h, as examples, to obtain either free amino-
phosphonate, N-protected monoester or N-protected phos-
phonic acid.
Protection of Aryl Phenyl Imines; General Procedure:
To a solution of acyl chloride or sulfonyl chloride (30 mmol) in anhyd
pyridine (150 mmol), the imine 4 (26.5 mmol) was added dropwise at
5–10°C, and the mixture was heated to 65°C for 2 h. A white solid
precipitated, then the mixture was cooled to –5°C and poured quickly
into 1 N aq HCl (250 mL). The solid was filtered, dried under vacuum
and then recrystallized (heptane). White crystals (yield: 41–95%)
were isolated and characterized by elemental analysis (Table 2).
Table 2. Characteristics of Compounds 5
In conclusion, we have developed a convenient and effi-
cient three-step procedure for the preparation of N-pro-
tected or unprotected Cα,α-disubstituted (diarylamino-
methyl)phosphonates which allows modulation of the
substituents on the carbon in the α-position to the phos-
phorus, as well as the protective group on the amine and
the phosphonate ester group.
Entry
Y
Ar
mp(°C)
(Solvent)
5a, h
5b
5c
5d
5e
5f
5g
5i
PhC(O)
PhC(O)
PhC(O)
o-tolylC(O)
MeC(O)
PhCH2OC(O)
Ts
Ph
o-tolyl
117 (heptane)
109–112 (heptane)
1-naphthyl 142–143 (heptane)
Ph
Ph
Ph
Ph
Ph
70 (heptane)
81 (heptane)
58–60 (heptane)
106–108 (heptane)
124–126 (heptane)
All the experiments were carried out under N2 with anhydrous sol-
vents. Mps were determined with a Metler FP5 and a Wild Leitz 350
apparatus. The compounds are characterized by 1H NMR
(200.132 MHz), 13C NMR (50.323 MHz) and 31P NMR (50.323
MHz). Elemental analyses were performed by the ”Service Central de
Microanalyse du CNRS”, in Montpellier. IR spectra were obtained
using a Perkin–Elmer Spectrum 1000 spectrophotometer. MS were
performed using FAB or EI (70 eV).
Ph2P(O)
a
All compounds gave satisfactory elemental microanalytical data:
C ± 0.41; H ± 0.37; N ± 0.46.
N-Protected Ca,a-Disubstituted (Aminomethyl)phosphonates 1;
General Procedure:
Diethyl phosphite (0.82 mL, 6.37 mmol) in anhyd THF (15mL) was
added, at –78°C, to a suspension of NaH (6.37 mmol) in anhyd THF
(15 mL). The mixture was held at –40°C for 30 min, then, at –78°C,
electrophile 5 (7 mmol) was slowly added. The mixture was stirred
for a further 12 h at 20°C, then treated with 1 N aq HCl (4 mL) at 0°C.
The aqueous layer was extracted with Et2O. After extraction, the or-
Imines 4; General Procedure:
To an arylmagnesium bromide solution prepared from magnesium
(1.25 g, 55.4 mmol), a catalytic amount of iodine and aryl bromide
(50 mmol) in Et2O (50 mL), at 25°C, was added benzonitrile(4.64 g,
45 mmol) in Et2O (40 mL). The mixture was stirred for 3 h. Then

SYNTHESIS
August 1998
1169
ganic layer was washed successively with aq Na2HCO3 and water un-
til the pH was neutral, dried (Na2SO4) and concentrated. An oil was
obtained, crystallizing after 12 h at 0°C. The white solid was recrys-
tallized with an appropriate solvent to give white crystals. (yield: 35–
96%).
1H NMR (CD3OD): δ = 1.11 t (6H, CH3, 3JH–H = 7.1 Hz); 2.33 s (3H,
CH3); 3.73 to 3.94 m (4H, OCH2); 4.99 s (2H, CH2); 6.23 d (1H, NH,
3JH–P = 10.3 Hz); 7.26 to 7.39 m (11H, aromatics) 7.60 to 7.66 (4H,
aromatics).
13C NMR (CD3OD): δ = 16.17 d (2C, CH3, 3JC–P = 5.7 Hz); 63.87 d
2
1
(2C, OCH2, JC–P = 7.6 Hz); 66.42 d (1C, Cα, JC–P = 147.4 Hz);
2
1a:
66.83 s (1C, CH2); 136.30 s (1C, Ci,); 137.59 d (2C, Ci, JC–P = 4.9
IR (KBr): ν = 1678 vs (C=O), 1277–1246 s (P=O), 1056–1018 cm–1 vs
Hz).
(P–O).
31P NMR (CDCl3): δ = 22.96.
1g:
3
4
1H NMR (CDCl3): δ = 1.13 dt (6H, CH3, JH–H = 7.1 Hz; JH–P
=
IR (KBr): ν = 1369 m (S=O), 1227 vs (P=O), 1049–1025 cm–1 vs
(P–O).
0.7 Hz) 3.9 m (4H, OCH2).
13C NMR (CDCl3): δ = 16.21 d (2C, CH3, JC–P = 5.7 Hz); 64.00 d
31P NMR (CDCl3): δ = 19.01.
3
2
1
(2C, OCH2, JC–P = 7.6 Hz); 67.26 d (1C, Cα, JC–P = 145.5 Hz);
1H NMR (CDCl3): δ = 1.14 t (6H, CH3, 3JH–H = 7.1 Hz); 2.33 s (3H,
CH3); 4.00 to 3.6 m (4H, OCH2); 7.01 to 7.25 m (10H, aromatics);
7.49 to 7.54 (4H, aromatics).
2
134.76 s (1C, Ci); 137.30 d (2C, Ci, JC–P = 4.5 Hz); 166.10 d (1C,
C=O, 3JC–P = 11.3 Hz).
13C NMR (CDCl3): δ = 16.54 d (2C, CH3, JC–P = 5.8 Hz); 21.39 s
3
2
1b:
(1C, CH3); 65.52 d (2C, OCH2, JC–P = 8.2 Hz); 70.19 d (1C, Cα,
IR (KBr): ν = 1683 vs (C=O), 1265–1236 s (P=O), 1054–1022 cm–1 vs
1JC–P = 152.2 Hz); 137.75 d (2C, Ci, 2JC–P = 4.2 Hz); 141.33 d (1C, Ci,
4JC–P = 0.6 Hz); 143.72 s (1C, Ci).
(P–O).
31P NMR (CDCl3): δ = 22.76.
1H NMR (CDCl3): δ = 1.14 and 1.20 dt (6H, CH3, JH–H = 7.1 Hz)
1h:
3
1.92 s (3H, CH3 ortho); 3.83 and 4.01 dm (4H, OCH2).
IR (KBr): ν = 1679 s (C=O), 1249 vs (P=O), 1024–1005 cm–1
s
13C NMR (CDCl3): δ = 16.29 and 16.48 dd {2C, CH3 (OEt), 3JC–P
=
(P–O).
5.7 and 5.2 Hz}; 21.88 d (1C, CH3, 4JC–P = 0.7 Hz); 63.67 and 63.78
31P NMR (CDCl3): δ = 23.66.
2
2
3
dd (2C, OCH2, JC–P = 7.4 and 7.9 Hz); 67.66 d (1C, Cα,1JC–P
=
1H NMR (CDCl3): δ = 4.68 dd (2H, HB, JH–H = 11.7 Hz; JH–P
=
2
3
151.0 Hz); 135.32 s (1C, Ci); 136.21 s (1C, Ci); 137.07 d (1C, Ci
8.4 Hz); 4.90 dd (2H, HA, JH–H = 11.7 Hz; JH–P = 7.4 Hz); 7.51 d
3
2
(Me), JC–P = 11.5 Hz); 138.54 d (1C, Ci, JC–P = 3.9 Hz); 165.15 d
(NH, 3JH–P = 7.3 Hz).
(1C, C=O, 3JC–P = 3.47 Hz).
13C NMR (CDCl3): δ = 67.60 d (1C, Cα, 1JC–P = 147.1 Hz); 69.05 d
(2C, OCH2, 2JC–P = 7.6 Hz); 134.50 s (1C, Ci); 136.02 d (2C, Ci, 3JC–P
= 6.1 Hz); 137.37 d (2C, Ci, 2JC–P = 4.2 Hz).
1c:
IR (KBr): ν = 1681 vs (C=O), 1243–1232 s (P=O), 1053–1031 vs
(P–O).
6:
31P NMR (CDCl3): δ = 23.08.
IR (KBr): ν = 1255 s (P=O), 1199 s (P=O), 1016 s (P–O), 953 cm–1
s
1H NMR (CDCl3): δ = 1.11 and 1.15 dt (6H, CH3, JH–H = 7.1 Hz);
(P–N).
3
3.83 and 4.02 dm (4H, OCH2).
31P NMR (CDCl3): δ = 31.41 d [1P, Ph2P(O), 2JP–P = 13.6 Hz]; 3.86 d
[1P, (EtO)2P(O), 2JP–P = 13.6 Hz].
13C NMR (CDCl3): δ = 16.29 and 16.33 dd (2C, CH3, 3JC–P = 5.7 and
5.1 Hz); 63.73 and 64.02 dd (2C, OCH2, 2JC–P = 7.4 and 7.9 Hz); 68.30
1H NMR (CDCl3): δ = 6.33 dd (1H, CH, JH–P = 13.6 Hz; JH–P
=
3
3
1
d (1C, Cα, JC–P = 149.8 Hz); 134.54 s (1C, Ci); 135.44 s (1C, Ci);
21.9 Hz); 7.19 to 7.41 m (12H, aromatics); 7.44 to 7.50 m (4H, aro-
matics).
138.65 d (1C, Ci, 2JC–P = 3.5 Hz); 165.40 d (1C, C=O, 3JC–P = 4.5 Hz).
13C NMR (CDCl3): δ = 64.75 s (1C); 132.14 d (1C, Cα, 1JC–P = 127.4 Hz).
1d:
IR (KBr): ν = 1675 vs (C=O), 1231 vs (P=O), 1060–1031 vs (P–O).
31P NMR (CDCl3): δ = 22.84.
Deprotection Studies; General Procedure:
Hydrogenolysis of Compound 1f:
3
4
1H NMR (CDCl3): δ = 1.12 dt (6H, CH3, JH–H = 7.1 Hz; JH–P
=
To a solution of 1f (0.27 g, 0.6 mmol) in anhyd MeOH (25mL) was
added Pd/C (0.02g). After consumption of the necessary hydrogen
volume, the mixture was filtered on Celite and the filtrate concentrat-
ed to give 7 as an oil (yield: 95%).
0.5 Hz); 2.43 s (3H, CH3 ortho); 3.79 and 3.97 m (4H, OCH2); 7.04 d
(NH, 3JH–P = 10.55 Hz).
3
13C NMR (CDCl3): δ = 16.20 d (2C, CH3, JC–P = 5.8 Hz); 19.87
2
s (1C, CH3); 63.84 d (2C, OCH2, JC–P = 7.7 Hz); 67.44 d (1C, Cα,
IR (KBr): ν = 3391 m (NH2), 1241 s (P=O), 1024 cm–1 s (P–O).
FAB+: (GT) M + H = 320.
1JC–P = 147.0 Hz); 136.25 s (1C, Ci); 136.73 s (1C, Ci); 137.49 d (2C,
Ci, 2JC–P = 4.3 Hz); 168.62 d (1C, C=O, 3JC–P = 10.3 Hz).
31P NMR (CDCl3): δ = 25.38.
1H (CDCl3): δ = 1.16 t (6H, CH3, 3JH–H = 7.1 Hz); 2.23 s (2H, NH2);
3.92 m (4H, OCH2, 3JH–H = 7.1 Hz); 7.27 m (6H, aromatics); 7.66 m
(4H, aromatics).
1e:
IR (KBr): ν = 1694 s (C=O), 1220 s (P=O), 1059–1031 cm–1 vs (P–O).
31P NMR (CDCl3): δ = 22.79.
3
13C NMR (CDCl3): δ = 16.32 d (2C, CH3, JC–P = 5.4 Hz); 62.97 d
3
4
1H NMR (CDCl3): δ = 1.08 dt (6H, CH3, JH–H = 7.1 Hz; JH–P
=
1
2
(1C, Cα, JC–P = 147.8 Hz); 63.14 d (2C, OCH2, JC–P = 7.4 Hz);
127.25 d (4C, Cm, 4JC–P = 1.2 Hz); 127.75 d (4C, Co, 3JC–P = 6 Hz);
128.07 s (2C, Cp); 142.37 s (2C, Ci).
0.5 Hz); 2.04 s (3H, CH3); 3.67 to 3.96 m (4H, OCH2); 6.78 d (NH,
3JH–P = 11.1 Hz).
3
13C NMR (CDCl3): δ = 16.13 d (2C, CH3, JC–P = 5.8 Hz); 24.23 s
(1C, CH3); 63.85 d (2C, OCH2, 2JC–P = 7.7 Hz); 67.13 d (1C, Cα, 1JC–
P = 146.7 Hz); 137.48 d (2C, Ci, 2JC–P = 4.5 Hz); 169.00 d (1C, C=O,
3JC–P = 10.8 Hz).
Hydrogenolysis of Compound 1h:
Using the same procedure, 9 was obtained as a white solid [mp 283–
285°C (MeOH/H2O); yield: 100%].
IR (KBr) : ν = 3430 w (NH), 1655 s (C=O), 1260 s (P=O), 1060 cm–1
s (P–O).
1f:
IR (KBr): ν = 1721 vs (C=O), 1243–1214 s (P=O), 1049–1017 cm–1 vs
FAB+: (GT) M + H = 368.
(P–O).
31P NMR (CD3OD): δ = 20.45.
31P NMR (CD3OD): δ = 22.26.

SYNTHESIS
Papers
1170
1H NMR (DMSO-d6): δ = 7.33 m (6H, aromatics), 7.53 m (7H, aro-
Franz, J. E. Discovery, Development and Chemistry of Glypho-
sate, In Herbicide Glyphosate; Grossbard, E.; Atkinson, D.,
Eds.; Butterworth: Boston, MA, 1985; p 1.
matics), 7.89 d (2H, aromatics, 3JH–H = 7.2 Hz), 8.96 d (1H, N2, 3JH–P
=
11.7 Hz).
13C NMR (CDCl3): δ = 67.08 d (1C, Cα, 1JC–P = 135.9 Hz); 126.96 s
(2C, Cp); 127.5 s (4C, Cm); 127.67 s (2C, Cm); 128.37 s (2C, Co);
128.52 d (4C, Co, 3JC–P = 4.68 Hz); 131.95 s (1C, Cp); 133.77 s (1C,
(3) Kafarski, P.; Mastalerz, P. Beiträge Zur Wirkstofforschung;
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(4) Bartels, G. Ger. Offen. DE 3,445,300, 1986; Chem. Abstr. 1987,
106, 50450z.
2
3
Ci); 139.43 d (2C, Ci, JC–P = 2 Hz); 168.19 d (1C, C=O, JC–P
=
5.9 Hz).
(5) Siepak, J., Pol. PL 138,019, 1987; Chem. Abstr. 1989, 110,
39184c.
Hydrolysis of Compound 1a:
Under weakly acidic conditions (pH 2.07, 40°C, 334 h), hydrolysis of
compound 1a (0.1g, 0.24 mmol) in a solution of H2O/EtOH/HCl
(1mL), gave, after evaporation, 9 as a white solid (yield: 100%).
Under basic conditions (pH 14, 40°C, 120 h), and after treatment with
1 N HCl, the hydrolysis of compound 1a (0.1 g, 0.24 mmol) in H2O/
EtOH/NaOH (1 mL), gave, on evaporation, the monoester compound
8 [mp 167°C (cyclohexane), yield: 60%].
(6) Siepak, J., Pol. PL 138,091, 1987; Chem. Abstr. 1989, 110,
24086y.
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IR (KBr): ν = 3430 w (NH), 1655 s (C=O), 1260 s (P=O), 1060 cm–1
s (P–O).
31P NMR (CDCl3): δ = 21.20.
1H NMR (CDCl3): δ = 1.02 t (3H, CH3, 3JH–H = 7.1 Hz); 3.7 dq (2H,
OCH2, 3JH–H = 7.3 Hz, 3JH–P = 7.6 Hz); 7.45 m (13H, aromatics); 7.83
m (2H, aromatics).
3
13C NMR (CDCl3): δ = 16.31 d (1C, CH3, JC–P = 5.9 Hz); 63.40 d
(1C, CH2, 2JC–P = 7.1 Hz); 67.83 d (1C, Cα, 1JC–P = 140.7 Hz); 127.36
s (2C, Cp); 128.21 s (4C, Cm); 128.31 s (2C, Cm); 128.51 s (4C, Co);
128.89 s (2C, Co), 132.57 s (1C, Cp); 133.24 s (1C, Ci); 138.90 s (2C,
Ci); 168.85 d (1C, C=O, 3JC–P = 3.1 Hz).
(16) Toniolo, C. Janssen Chimica Acta, 1993, 11, 10.
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