O,O-Diphenyl N-sulfonylbenzimidoylphosphonates, a novel type of C-phosphorylated imines

Article abstract of DOI:10.1007/s11172-006-0171-9

A preparative method for the synthesis of first representatives of O,O-diphenyl N-sulfonylbenzimidoylphosphonates was proposed. The method involves oxidation of the corresponding α-(sulfonylamino)benzylphosphonates. The σ-constants of the N-sulfonylbenzim

Full text of DOI:10.1007/s11172-006-0171-9

2652
Russian Chemical Bulletin, International Edition, Vol. 54, No. 11, pp. 2652—2655, November, 2005
O,OꢀDiphenyl Nꢀsulfonylbenzimidoylphosphonates,
a novel type of Cꢀphosphorylated imines*
Yu. V. Rassukana, A. A. Sinitsa, and P. P. Onys´koꢀ
Institute of Organic Chemistry, National Academy of Sciences of the Ukraine,
5 ul. Murmanskaya, 02094 Kiev, Ukraine.
Fax: +7 (044) 573 2643. Eꢀmail: onysko@rambler.ru
A preparative method for the synthesis of first representatives of O,Oꢀdiphenyl Nꢀsulꢀ
fonylbenzimidoylphosphonates was proposed. The method involves oxidation of the correꢀ
sponding αꢀ(sulfonylamino)benzylphosphonates. The σꢀconstants of the Nꢀsulfonylbenzꢀ
imidoylphosphonate group were estimated by 19F NMR spectroscopy. The imidoylphosphonates
obtained easily formed stable adducts at the C=N bond with Pꢀ and Oꢀnucleophiles.
Key words: imidoylphosphonates, αꢀamino phosphonates, sulfonamides, oxidation,
σꢀconstants.
Esters of imino phosphonic acids (imidoylphosꢀ
imidoylphosphonates and studied some of the properties
phonates) are important precursors in the synthesis of
functionalized amino phosphonic acids combining a numꢀ
ber of practically valuable properties.1 For synthetic purꢀ
poses, imines with electronꢀwithdrawing substituents at
the N atom are particularly attractive because of their
enhanced reactivities. NꢀSulfonylimines of carbonyl comꢀ
pounds have found wide use in synthetic practice.2 Howꢀ
ever, examples of such imines with a phosphoryl group at
the azomethine C atom are few,3 while Nꢀsulfonylꢀ
benzimidoylphosphonates have not been documented so
far. In the series of imidoylphosphonates, only alkyl and
silyl esters are known.1 Aryl imidoylphosphonates have
not been obtained hitherto because of the absence of apꢀ
propriate synthetic procedures. In particular, reactions of
imidoyl chlorides with phosphites cannot be applied for
this purpose since the Arbuzov reaction is not characterꢀ
istic of aryl esters of PIII acids. An unusual synthesis of
diphenyl benzimidoylphosphonates has been described
involving reactions of the Schiff bases with diphenyl
phosphorochloridate and triethylamine.4 We failed to reꢀ
produce this reaction with Nꢀbenzylideneaniline as an
example: the starting reagents remained virtually unꢀ
changed under the specified4 conditions and the cited
results were probably erroneous.
of this novel type of Nꢀsulfonylimines.
Results and Discussion
Our approach to the synthesis of O,Oꢀdiphenyl
Nꢀ(phenylsulfonyl)fluorobenzimidoylphosphonates is
shown in Scheme 1.
Scheme 1
Alkyl imidoylphosphonates are alkylating agents and
their functionalization can be accompanied by Nꢀalkylaꢀ
tion as side reactions. Such processes are not characterisꢀ
tic of aryl esters. In the present work, we developed a
method for the synthesis of O,Oꢀdiphenyl Nꢀsulfonylbenzꢀ
Ar = 4ꢀFC6H4 (a); 3ꢀFC6H4 (b)
Initially, a threeꢀcomponent condensation of benzꢀ
aldehydes 1, diphenyl phosphite 2, and benzenesulfonꢀ
amide 3 in acetyl chloride as a condensation agent gives
* Dedicated to the Corresponding Member of the Russian Acadꢀ
emy of Sciences T. A. Mastryukova.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2567—2570, November, 2005.
1066ꢀ5285/05/5411ꢀ2652 © 2005 Springer Science+Business Media, Inc.

NꢀSulfonylbenzimidoylphosphonates
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 11, November, 2005 2653
αꢀ(phenylsulfonylamino)benzylphosphonates 4, which are
further oxidized with a Py—Cl2 system into benzimidoylꢀ
phosphonates 5 in high yields. The conversion 4→5 is the
key step of the synthesis and probably3,5 involves chloriꢀ
nation of the N atom of sulfonamide 4 followed by elimiꢀ
nation of HCl from intermediate Nꢀchloro sulfonamide A
(see Scheme 1).
[αꢀ(Phenylsulfonylamino)ꢀ4ꢀfluorobenzyl]diphenylꢀ
phosphine oxide (6) obtained according to Scheme 2
yielded no phosphorylated imine in the reaction with
Py—Cl2 under similar conditions, which agrees with our
previous data.3
acceptor exceeding substantially the imidoylphosphonate
group with the Nꢀbenzyl substituent in the withdrawing
strength: for PhCH2N=C[P(O)(OEt)2]—, σI = 0.34 and
σR = 0.02 (see Ref. 9). Replacement of the Nꢀbenzyl
substituent by the sulfonyl one affects the resonance
σꢀconstant (∆σR = 0.18) to a larger extent than the inducꢀ
tive σꢀconstant (∆σI = 0.09), which suggests higher polarꢀ
izability of the C=N bond in sulfonylimines.
High electronꢀwithdrawing ability of the sulfonylꢀ
imidoyl group predetermines an increased reactivity of
the C=N bond in imines 5. For instance, imidoylꢀ
phosphonate 5a readily reacts with Pꢀ and Oꢀcentered
nucleophiles at 20 °C even in the absence of bases to give
stable (under normal conditions) compounds 7 and 8
containing the αꢀ(phenylsulfonylamino)benzylphosphonꢀ
ate fragment (Scheme 3).
Scheme 2
Scheme 3
Compounds 5 are the first representatives of imidoylꢀ
phosphonates with aryloxy groups linked to the P atom.
They are crystalline substances that are stable in dry atꢀ
mosphere but are easily hydrolyzed in air.
The spectroscopic data for sulfonylimines 5 are in full
agreement with their structures. The 1H NMR spectra
contain no signals for the CH—NH fragment. The IR
spectra show an intense band of the C=N stretching viꢀ
brations (1640—1650 cm–1). The band of the P=O bond
(1280 cm–1) is shifted by 20 to 30 cm–1 to the higher
frequencies compared to the starting phosphonates 4
(1250—1260 cm–1), which is consistent with the effect of
the withdrawing imidoyl substituent. The positions of sigꢀ
nals for phosphorus nuclei in the 31P NMR spectra (δ –5.9
to –5.2), which are typical of imidoylphosphonates,1 are
most convenient for structural identification. The presꢀ
ence of the P—C=N fragment was confirmed by the
13C NMR spectra showing a signal for the sp2ꢀC atom of
the imino group with a high direct coupling constant with
the phosphorus nuclei (δC ~175, 1JC,P = 204 Hz).
Magnetic shielding of the fluorine nuclei in substiꢀ
tuted fluorobenzenes depends on the electronic paramꢀ
eters of substituents in the benzene ring and is widely used
for their quantitative determination.6,7 Measuring the
chemical shifts of the F nuclei in the 19F NMR spectra of
imidoylphosphonates 5 (CDCl3, fluorobenzene as the inꢀ
ternal standard) and using the Taft relations8
Benzimidoylphosphonates containing the Nꢀalkyl or
Nꢀbenzyl group react with neither Pꢀ nor Oꢀnucleophiles
in the absence of bases.
An interesting spectral feature of compound 7 with
two nonequivalent geminal Pꢀcontaining groups at the
carbon atom is the manifestation of a longꢀrange spinꢀ
spin coupling between the phosphorus and fluorine
nuclei, the coupling constant for the Ph2P(O) group
(6JP,F = 5 Hz) being substantially higher than that for the
(PhO)2P(O) substituent (6JP,F = 1 Hz). For monoꢀ
phosphorylated derivatives 4a and 6, the relationship beꢀ
6
tween the coupling constants is opposite: JP,F = 4.5 and
3 Hz, respectively.
Thus, imidoylphosphonates of the type 5 are promisꢀ
ing precursors in the synthesis of polyfunctional derivaꢀ
tives of αꢀamino phosphonic acids.
σ = (δm + 0.6)/7.1
σ
R = (δ F – δ F)/29.5,
p m
I
we estimated for the first time the inductive and resoꢀ
nance σꢀconstants of the Nꢀsulfonylbenzimidoylphosꢀ
phonate group (PhSO2N=C[P(O)(OPh)2]—): σI = 0.43,
σR = 0.20, and σp = σI + σR = 0.63. Hence, the Nꢀsulꢀ
fonylbenzimidoylphosphonate group is a strong electron
Experimental
1
H, 19F, and 31P NMR spectra were recorded on a Varian
VXRꢀ300 NMR spectrometer (299.95, 282.20, and 121.42 MHz,

2654
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 11, November, 2005
Rassukana et al.
respectively). Chemical shifts are referenced to Me4Si (1H) and
CFCl3 and PhF (19F) as the internal standards and to 85%
H3PO4 as the external standard (31P). IR spectra were recorded
on a URꢀ20 instrument in KBr pellets or as solutions in CCl4.
Solvents were thoroughly purified and dried according to stanꢀ
dard methods. Aldehydes 1, sulfonamide 3, chloro(dipheꢀ
nyl)phosphine (Merck), diphenyl phosphite 2, and diphenylꢀ
phosphine oxide (SigmaꢀAldrich) were used.
Synthesis of phosphonates 4 (general procedure). Sulfonꢀ
amide 3 (2.67 g, 17 mmol) was added to a stirred solution of
diphenyl phosphite 2 (3.98 g, 17 mmol) in AcCl (50 mL). The
mixture was stirred for 2 h and then aldehyde 1 (2.11 g, 17 mmol)
was added. The reaction mixture was left for 16 h. The solvent
was removed and the residue was washed with ether and dried
in air.
O,OꢀDiphenyl Nꢀ(phenylsulfonyl)ꢀ3ꢀfluorobenzimidoylphosꢀ
phonate (5b). The yield was 72%, m.p. 90 °C. Found (%):
C, 60.41; H, 3.91; P, 6.18. C25H19FNO5PS. Calculated (%):
C, 60.60; H, 3.87; P, 6.25. IR (CCl4), ν/cm–1: 1180, 1350 (S=O);
1
1280 (P=O); 1650 (C=N). H NMR (CDCl3), δ: 7.03 (d, 4 H,
3JH,H = 8 Hz); 7.12—7.24 (m, 8 H); 7.44—7.55 (m, 4 H); 7.62
3
(t, 1 H, JH,H = 8 Hz); 7.83 (m, 2 H). 13C NMR (CDCl3), δ:
115.7 (dd, C(2), ArF, 2JC,F = 24 Hz, 3JC,P = 4.3 Hz); 119.3 (d,
2
3
C(4), ArF, JC,F = 21.6 Hz); 120.2 (d, C(2), PhO, JC,P =
4.5 Hz); 124.4 (dd, C(6), ArF, JC,P = 4.4 Hz, 4JC,F = 2.4 Hz);
3
125.7 (s, C(4), PhO); 127.8 (s, C(4), PhSO2); 129.0 (s, C(3),
3
PhSO2); 129.7 (s, C(3), PhO); 130.2 (d, C(5), ArF, JC,F
=
2
3
7 Hz); 134.8 (dd, CC=N, JC,P = 28 Hz, JC,F = 8 Hz);
139.3 (s, CSO2); 149.9 (d, C—O, JC,P = 9 Hz); 161.9 (d,
C—F, JC,F = 249 Hz); 174.6 (d, C=N, JC,P = 204 Hz).
19F NMR (CDCl3), δ: –111.16 (CFCl3); 2.48 (PhF). 31P NMR
(CDCl3), δ: –5.9.
2
1
1
O,OꢀDiphenyl αꢀ(phenylsulfonylamino)ꢀ4ꢀfluorobenzylphosꢀ
phonate (4a). The yield was 49%, m.p. 181—182 °C. Found (%):
C, 60.47; H, 4.14; P, 6.11. C26H21FNO5PS. Calculated (%):
C, 60.36; H, 4.25; P, 6.23. IR (KBr), ν/cm–1: 1180, 1350 (S=O);
Nꢀ[(Diphenylphosphinoyl)(4ꢀfluorophenyl)methyl]benzeneꢀ
sulfonamide (6). Aldehyde 1a (0.68 g, 5.5 mmol) and chloro(diꢀ
phenyl)phosphine (1 g, 4.5 mmol) were added to a solution of
benzenesulfonamide (0.71 g, 4.5 mmol) in glacial AcOH (10 mL)
and the reaction mixture was refluxed for 3 h. The solvent was
removed and the residue was washed with ethanol and crystalꢀ
lized from EtOH—CHCl3 (1 : 3). The yield of compound 6 was
1.4 g (66%), m.p. 254 °C. Found (%): C, 64.62; H, 4.42; S, 6.63.
C25H21FNO3PS. Calculated (%): C, 64.51; H, 4.55; S, 6.89.
IR (KBr), ν/cm–1: 1170, 1340 (S=O); 1198 (P=O). 1H NMR
(CDCl3), δ: 5.23 (dd, CH, 1 H, 2JH,P= 9.9 Hz, 3JH,H= 9.5 Hz);
6.5 (m, 2 H); 6.9 (m, 2 H); 7.1 (m, 2 H); 7.40—8.10 (m, 14 H).
19F NMR (CDCl3), δ: –114.56 (CFCl3). 31P—{H} NMR
(CDCl3), δ: 32.6 (d, 6JP,F = 3 Hz).
O,OꢀDiphenyl αꢀdiphenylphosphinoylꢀαꢀ(phenylsulfonylamiꢀ
no)ꢀ4ꢀfluorobenzylphosphonate (7). Diphenylphosphine oxide
(0.035 g, 0.17 mmol) was added to a solution of imidoylꢀ
phosphonate 5a (0.086 g, 0.17 mmol) in benzene (5 mL). After
1 h, the solvent was removed and the residue was washed with
light petroleum. The yield of compound 7 was 0.11 g (91%),
m.p. 146—148 °C. Found (%): C, 63.87; H, 4.28; P, 9.03.
C37H30FNO6P2S. Calculated (%): C, 63.70; H, 4.33; P, 8.88.
IR (KBr), ν/cm–1: 1180, 1350 (S=O); 1210, 1280 (P=O); 3180
(NH). 1H NMR (CDCl3), δ: 4.86 (br., 1 H, NH); 6.18 (m, 2 H);
1
1250 (P=O); 3280 (NH). H NMR (CDCl3), δ: 5.23 (dd, 1 H,
2
3
CH, JH,P = 25 Hz, JH,H = 9.6 Hz); 6.68—6.82 (m, 5 H, Ar,
NH); 7.13—7.22 (m, 10 H, Ar); 7.29—7.33 (m, 3 H, Ar); 7.52 (d,
2 H, Ar, 3JH,H = 8 Hz). 19F NMR (CDCl3), δ: –113.39 (CFCl3).
31P NMR (CDCl3), δ: 12.1 (2JP,H = 25 Hz); 31P—{H} NMR, δ:
12.1 (d, 6JP,F = 4.4 Hz).
O,OꢀDiphenyl αꢀ(phenylsulfonylamino)ꢀ3ꢀfluorobenzylphosꢀ
phonate (4b). The yield was 56%, m.p. 200 °C. Found (%):
C, 60.23; H, 4.28; P, 6.37. C26H21FNO5PS. Calculated (%):
C, 60.36; H, 4.25; P, 6.23. IR (KBr), ν/cm–1: 1180, 1350 (S=O);
1
1260 (P=O); 3250 (NH). H NMR (CDCl3), δ: 5.25 (dd, 1 H,
2
3
3
CH, JH,P = 26 Hz, JH,H = 9.9 Hz); 6.74 (d, 2 H, Ar, JH,H
=
3
3
8 Hz); 6.83 (dd, 1 H, NH, JH,H = 9.9 Hz, JH,P = 10 Hz);
3
6.92—7.35 (m, 15 H, Ar); 7.47 (d, 2 H, Ar, JH,H = 8 Hz).
19F NMR (CDCl3), δ: –115.49 (CFCl3). 31P NMR (CDCl3), δ:
11.6 (d, 2JP,H= 26 Hz).
Synthesis of imidoylphosphonates 5 (general procedure). Pyꢀ
ridine (1.27 g, 16 mmol) was added dropwise to a stirred solution
of chlorine (6.24 g, 8.8 mmol) in CCl4 (25 mL) with ice cooling.
The reaction mixture was warmed to room temperature and
phosphonate 4 (3.98 g, 8 mmol) was added portionwise with
stirring. After 8 h, the precipitate that formed was filtered off,
the solvent was removed, and the residue was washed with light
petroleum.
3
3
6.47 (t, 1 H, JH,H = 8 Hz); 6.73 (d, 2 H, JH,H = 8 Hz);
3
3
6.95—7.54 (m, 22 H); 7.89 (dd, 1 H, JH,H = 8 Hz, JH,F
=
O,OꢀDiphenyl Nꢀ(phenylsulfonyl)ꢀ4ꢀfluorobenzimidoylphosꢀ
phonate (5a). The yield was 68%, m.p. 93 °C. Found (%):
C, 60.84; H, 3.95; P, 6.34. C25H19FNO5PS. Calculated (%):
C, 60.60; H, 3.87; P, 6.25. IR (CCl4), ν/cm–1: 1180, 1350 (S=O);
1280 (P=O); 1640 (C=N). 1H NMR (CDCl3), δ: 7.02 (d,
5.7 Hz); 8.02 (dd, 1 H, 3JH,H = 8 Hz, 3JH,F = 5.7 Hz). 19F NMR
(CDCl3), δ: –113.96 (CFCl3). 31P—{H} NMR (CDCl3), δ: 8.75
2
6
(dd, 1 P, POPh, JP,P = 12 Hz, JP,F = 1 Hz); 37.94 (dd, 1 P,
PPh, 2JP,P = 12 Hz, 6JP,F = 5 Hz).
O,OꢀDiphenyl αꢀmethoxyꢀαꢀ(phenylsulfonylamino)ꢀ4ꢀfluoroꢀ
benzylphosphonate (8). A solution of imidoylphosphonate 5a
(0.15 g) in anhydrous methanol (10 mL) was left at room temꢀ
perature for 12 h. The solvent was removed and the residue was
crystallized from diethyl ether—light petroleum (1 : 2). The
yield of compound 8 was 0.16 g (90%), m.p. 146—148 °C.
Found (%): C, 58.89; H, 4.42; P, 6.11. C26H23FNO6PS. Calcuꢀ
lated (%): C, 59.20; H, 4.39; P, 5.87. IR (KBr), ν/cm–1: 1180,
1350 (S=O); 1280 (P=O); 3200 (NH). 1H NMR (CDCl3), δ:
3.58 (s, 3 H, OMe); 6.60 (d, 1 H, NH, 3JH,P = 8.7 Hz); 6.86 (m,
3
3
4 H, JH,H= 8 Hz); 7.11—7.23 (m, 8 H); 7.50 (t, 2 H, JH,H
=
=
3
3
8 Hz); 7.61 (t, 1 H, JH,H = 8 Hz); 7.83 (d, 2 H, JH,H
8 Hz); 7.94 (dd, 2 H, 3JH,H = 8 Hz, 3JH,F = 5.7 Hz). 13C NMR
(CDCl3), δ: 115.8 (d, C(3), ArF, 2JCF = 22 Hz); 120.3 (d, C(2),
3
PhO, JC,P = 3.8 Hz); 125.7 (s, C(4), PhO); 127.7 (s, C(2),
PhSO2); 129.0 (s, C(3) PhSO2); 129.7 (s, C(3), PhO); 129.3
2
4
(dd, CC=N, JC,P = 25 Hz, JC,F = 2.5 Hz); 131.8 (dd, C(2),
3
3
ArF, JCP = 9.2 Hz, JC,F = 4.9 Hz); 133.59 (s, C(4), PhSO2);
139.6 (s, CSO2); 150.0 (d, C—O, JC,P = 10 Hz); 165.1 (d,
C—F, JC,F = 255 Hz); 174.7 (d, C=N, JC,P = 204 Hz).
19F NMR (CDCl3), δ: –105.09 (CFCl3); 7.42 (PhF). 31P NMR
(CDCl3), δ: –5.2.
2
1
1
3
4 H, Ar); 7.41 (t, 2 H, Ar, JH,H = 8 Hz); 7.54—7.62 (m,
6 H, Ar). 19F NMR (CDCl3), δ: –113.75 (CFCl3). 31P NMR
(CDCl3), δ: –8.50.

NꢀSulfonylbenzimidoylphosphonates
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 11, November, 2005 2655
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Received March 15, 2005;
in revised form August 2, 2005