Oxidation of diethyl N-sulfinylphosphoramidates

Article abstract of DOI:10.1002/hc.20474

It is reported that the diethyl N-sulfinylphosphoramidate (1a) is oxidized with iodoso-and/or iodoxybenzene as well as with organic peroxides, to give diethyl N-sulfonylphosphoramidate (7a). The latter was generated in situ at low temperature and trapped

Full text of DOI:10.1002/hc.20474

Heteroatom Chemistry
Volume 19, Number 5, 2008
Oxidation of Diethyl N-Sulfinylphos-
phoramidates
Graz˙yna Mielniczak and Andrzej Lꢀ opusin´ski
Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences,
Department of Heteroorganic Chemistry, Sienkiewicza 112, 90-363 Lo´dz´, Poland
Received 15 November 2007; revised 17 April 2008
The reaction of their formation, as short-lived
ABSTRACT: It is reported that the diethyl N-
sulfinylphosphoramidate (1a) is oxidized with iodoso-
and/or iodoxybenzene as well as with organic perox-
ides, to give diethyl N-sulfonylphosphoramidate (7a).
The latter was generated in situ at low temperature
and trapped with dialkyl phosphoramidates, afford-
ing the N,Nꢀ bis(dialkyl phosphor)sulfamides 3a–c.
The oxidation of 1a with cumene peroxide in the
presence of 2,2-dimethyl-propan-1-ol (9) produced
the diethylphosphor-N-[2,2-dimethylpropyl]sulfamate
intermediate products, was documented also in the
hydrolysis and ammonolysis of sulfamate esters [12].
The electrophilic reactivity of sulfonylamines was
demonstrated by their additions to unsaturated sys-
tems. Amongst them, the [2+2] cycloaddition re-
actions of N-sulfonylamines to olefin are known
as a convenient route to the synthesis of the 1,2-
thiazetidine-1,1-dioxides, β-sultam [13].
The latter one, being a derivative of taurine and
sulfonyl analogs of β-lactams, still merits an investi-
gation as a compound with potential applications in
bioorganic and medical chemistry [14–20].
In this paper, the results of our studies on the
oxidation of the sulfinyl sulfur atom in diethyl N-
sulfinylphosphoramidate (1a) as a route to diethyl
N-sulfonylphosphoramidate (7a) as an intermediate
compound are described.
ꢁ
C
(10a). 2008 Wiley Periodicals, Inc. Heteroatom Chem
19:530–536, 2008; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/hc.20474
INTRODUCTION
N-sulfonylamines, the structural analogs of sulfur
trioxide, have been prepared previously [1–3] and
are used as highly reactive electrophiles [4–11]. They
are mostly available by the dehydrohalogenation of
sulfamic acid chlorides as a compound stable only
at low temperature in the solution (Eq. (1)).
RESULTS AND DISCUSSION
Our earlier approach to the synthesis of N-phosphor-
yl sulfamoyl chloride, the substrate for the prepara-
tion of N-sulfonylphosphoramidate, was unsuccess-
ful [21].
It is reasonable to mention that the oxida-
tion reaction of sulfinyl group in N-sulfinylphos-
phoramidate should be considered as a potential
route to the synthesis of such compounds. The syn-
thetic approach to N-sulfonylamines by the oxida-
tion reaction of thionitrozoarenes, followed by the
participation of arenesulfinylamines as intermediate
products, was demonstrated [22].
Correspondence to: Andrzej Lꢀ opusin´ski; e-mail: lopuch@cbmm.
lodz.pl.
c
ꢀ
2008 Wiley Periodicals, Inc.
530

Oxidation of Diethyl N-Sulfinylphosphoramidates 531
SCHEME 1
Dialkyl N-sulfinylphosphoramidates are known
and being prepared as stable compounds by the reac-
tion of the corresponding phosphoramidates and/or
their N-silylated analogs with thionyl chloride [23–
26] or N-(chlorosulfinyl)imidazole [27].
We have found that diethyl N-sulfinylphos-
phoramidate (1a) (Scheme 1, reaction (A)) reacts at
20◦C in acetonitrile with 1 eq. of iodosobenzene (2).
The formation of two products, namely the N,Nꢀ-
bis(diethyl phosphor)sulfamide (3a) and diethyl
phosphoramidate (4a), was registered by 31P NMR
in this reaction (Scheme 1).
SCHEME 3
The similar reaction performed between 1a and
0.5 eq. iodoxybenzene (5) in the presence of 1 eq.
amidate 4a in dichloromethane at −10◦C results in
the formation of sulfamide 3a in nearly quantitative
yield (reaction (B)). The sulfamide 3a is also formed
in this reaction when cumene peroxide and/or t-butyl
peroxide is used as an oxidizing agent. Without the
oxidant, a 1:1 mixture of 1a and 4a does not react in
dichloromethane solution at 20◦C. In the reaction
between N-sulfinylphosphoramidate 1a and diiso-
propyl phosphoramidate (4b) (1:1 ratio) performed
in the presence of 0.5 eq. of 5, the formation of four
identified compounds, 3a, 3b, 3c, 4a, was confirmed
by 31P NMR (Scheme 2).
The products formed during the reaction, as
shown in Scheme 2, were identified by comparing
their 31P shifts values with those characteristic for
the compounds obtained independently (3a, 3b and
4a). The addition of an excess of pyridine to this
mixture of products resulted in the shift of the reso-
nance lines, ascribed to the compounds 3a, 3b and
3c for 3–4 ppm, toward lower field as a result of the
formation of their pyridinium salts [21]. In addition,
in the MS FABpositive ion spectra registered for the
reaction mixture, in the presence of traces of sodium
chloride, the mass peaks, corresponding to the clus-
ter ions: 6a, m/z 413.2, [M(3a) − H + 2Na]+; 6b, m/z
469, [M(3b) − H + 2Na]+; 6c, m/z 441, [M(3c) − H
+ 2Na]+, respectively, were detected, providing fur-
ther evidence for the correct identification of the
putative products 3a, 3b, and 3c (Scheme 2). The
strongly acidic properties of N,Nꢀ-bis-(dialkyl phos-
phor)sulfamides 3a–c were demonstrated by the ex-
ample of pure 3a recently in [21].
The obtained results of the reaction of diethyl
N-sulfinylphosphoramidate (1a) with iodoso-, io-
doxybenzene, and organic peroxides give a clear
evidence that these reactions occurred with the for-
mation of a short-lived, electrophilic intermediate,
diethyl N-sulfonylphosphoramidate (7a). This inter-
mediate was trapped immediately by the amidate 4a
or 4b with the formation of the corresponding N,Nꢀ-
bis(dialkyl phosphor)sulfamides, most probably in
the reaction as shown in Scheme 3.
Although we tried to keep the reaction mix-
ture under completely anhydrous condition, it is
SCHEME 2
Heteroatom Chemistry DOI 10.1002/hc

532 Mielniczak and Lꢀopusin´ski
important to state that iodosobenzene cannot be ob-
tained as an absolutely dry compound.
Dialkyl N-sulfinylphosphoramidates are ex-
tremely sensitive toward traces of water. In the pres-
ence of water, they are immediately transformed into
the corresponding phosphoramidates [24].
The performed oxidations of N-sulfinylphos-
phoramidate 1a by iodosobenzene (2), and/or io-
doxybenzene (5) in the presence of benzyl alcohol,
ethanol, or phenol, in dichloromethane in the wide
range of temperature, gave no evidence of formation
of the N-phosphoryl sulfamates in these reactions.
However, in the reaction of 1a with cumene perox-
ide (8) in the presence of 2,2-dimethyl-propan-1-ol
(9) at low temperature in dichloromethane the for-
mation of two products was observed in the 31P NMR
spectra.
The formation of the unsymmetrical sulfamide
3c with nitrogen atoms substituted by different di-
alkoxy phosphoryl groups in the discussed process
(Scheme 2) is the result of the reaction between N-
sulfonylphosphoramidate 7a and amidate 4b. The
other product formed in 10% yield in this reac-
tion was identified as an N,Nꢀ-bis(diisopropyl phos-
phor)sulfamide (3b). Its formation was rather unex-
pected since diisopropyl N-sulfinylphosphoramidate
(1b) was not used as the substrate of the reaction.
However, in the independent experiment we es-
tablished that the transfer of the sulfinyl group from
diethyl N-sulfinylphosphoramidate (1a) to the phos-
phoryl atom of diisopropyl phosphoramidate 4b
took place. The formed N-sulfinylphosphoramidate
1b undergoes the oxidation to the corresponding di-
isopropyl N-sulfonylphosphoramidate (7b), which is
trapped by the amidate 4b to give a symmetrical sul-
famide 3b.
One of them was identified as an amidate 4a. The
second one resonating at δ −2.36 is most probably
diethyl phosphor N-(2,2-dimethylpropyl)sulfamate
(10a). In the MS FAB spectra of the crude reac-
tion mixture, lines of mass m/z 154 [M + 1] amidate
4a and m/z 302 [M + 1], characteristic for 10a, were
found. The attempts to isolate the putative ester 10a
by a column chromatography failed.
The mixture of 1:1 molar equivalents of N-sul-
finylphosphoramide 1a and amide 4b reacts at room
temperature in dichloromethane solution, and after
4 h the formation of the composition the prod-
ucts, shown in Eq. (2) was registered by 31P NMR.
In the similar reaction of 1a with 0.5 eq. of 5
performed in the presence of 9-phenylfluorenol (11),
The similar transsulfinylation reaction of
phenylenediamine and other amines, by the N-
sulfinylaniline, was previously reported [28].
The alternative route to the formation of the un-
symmetrical substituted sulfamide 3c, the transpho-
sphorylation reaction between 3a and amide 4b as
well 3b, was excluded.
Besides phosphoramidates, alcohols can be used
for the trapping the short-lived N-sulfonylphos-
phoramidates, yielding the esters of the N-phos-
phoryl sulfamic acid [21].
An example of N-phosphoryl sulfamate was
synthesized only recently, in the reaction of n-octyl-
sulfamate with trialkyl phosphite in the presence
of diisopropylazodicarboxylate and subsequent
isomerization of the formed phosphazene with
DABCO [29].
the formation of three products, shown in Scheme 4,
was registered by 31P NMR spectroscopy. In the MS
FAB negative ions spectra of the reaction solution,
among the lines corresponding to products 3a, 4a,
and 12, a signal m/z 456 [M − 1], characteristic for di-
ethyl phosphoramido-9-phenylofluorenyl sulfite 13b
was observed.
The oxidation of N-sulfinylphosphoramidate 1a
in the presence of alcohol seems to be rather a com-
plex reaction. In the first step, the reaction per-
formed at low temperature by addition of oxidant
to the solution of 1a, the formation of N-sulfonyl-
phosphoramidate 7a should take place. This reac-
tive intermediate could interact with corresponding
alcohol, introduced in the second step yielding the
sulfamate (10a).
Heteroatom Chemistry DOI 10.1002/hc

Oxidation of Diethyl N-Sulfinylphosphoramidates 533
SCHEME 4
On the other hand, the direct reaction between
Further studies on the oxidation of N-sulfinyl-
phosphoramidates as a possible route to the N-sul-
fonylphosphoramidates, the precursors of N-phos-
phorylated β-sultams, are in progress.
alcohol and N-sulfinylphosphoramidate 1a cannot
be excluded. This possibility led to the formation of
amidosulfites 13a and 13b. Their subsequent oxi-
dation providing corresponding sulfamates 10a,b is
also possible. However, the value of m/z characteris-
tic for 10b was not found in the mass spectra of the
reaction solution.
EXPERIMENTAL
The solvents and reagents were purified by stan-
dard procedures before use. The column rapid chro-
matography was performed on Merck silica gel
(60 mesh). 1H NMR spectra were determined at
200.13 MHz with a Bruker AC 200 spectrometer us-
ing TMS as internal standard. 31P NMR was taken
on a Bruker AC 200 spectrometer at 81 MHz. Posi-
tive chemicals shifts are downfield from 85% H3PO4
used as an external reference. 1H and 31P NMR spec-
tra were recorded in the presence of dried deute-
rochloroform. The MS spectra were recorded on
Finnigan MAT 95 spectrometer in glycerol matrix us-
ing cesium as the primary ion beam. The substrates,
diethyl N-sulfinylphosphoramidate (1a) [23,24],
iodosobenzene (2) [31], iodoxybenzene (5) [32],
diethyl phosphoramidate (4a) [33], diisopropyl
phosphoramidate (4b) [34], and N,Nꢀ-bis(diethyl
phosphor) sulfamide (3a) [21], were prepared as
described in the literature.
It is assumed that the reaction of simple alkyl
alcohols with N-sulfinylamines and amides first led
to the corresponding sulfinyl esters, which are un-
stable and cannot be isolated from the reaction so-
lution. However, it was reported that in the reaction
between p-toluenesulfinylamide and 11, a relatively
stable sulfinyl ester was formed. This was slowly
decomposed in the reaction solution, with the for-
mation of p-toluenesulfonyl 9-phenylfluorenylamide
[30]. We assume that the amide 12 isolated from the
reaction depicted in Scheme 5 is most probably the
product of such decomposition of initially formed
sulfinyl ester 13b. The presence of compound 13b
in the reaction mixture was confirmed by MS spec-
trometry. The formation of the sulfamate 10a as a
reaction product (Scheme 3) may also be the result
of the oxidation of sulfinyl ester 13a. The obtained
experimental data cannot give a convincing proof of
these possible routes for the formation of 10a.
Oxidation of Diethyl N-Sulfinylphos-
phoramidate (1a)
By Iodosobenzene (2). The suspension of 0.092
g (0.42 mmol) of 2 in the solution of 0.085 g (0.42
mmol) 1a in 10 mL dry acetonitrile was stirred
for 1 h at room temperature. After this time, the
presence of two products, diethyl phosphoramidate
(4a), δ 9.6 ppm (65%), and N,Nꢀ-bis(diethyl phos-
phor)sulfamide (3a), δ −5.9 ppm (13%), as well ca.
22% of not identified product was registered in the
reaction mixture by 31P NMR.
By Iodoxybenzene (5) in the Presence of Amidate
4a. To the stirred solution of 0.04 g (0.2 mmol) N-
sulfinylphosphoramidate 1a and 0.03 g (0.2 mmol)
of 4a in 5 mL of dichloromethane, cooled to −10◦C,
SCHEME 5
Heteroatom Chemistry DOI 10.1002/hc

534 Mielniczak and Lꢀopusin´ski
0.023 g (0.1 mmol) of iodoxybenzene (5) in 5 mL
dry dichloromethane was added. The stirring was
continued for 2 h at this temperature. The solvent
was removed under reduced pressure. In the inte-
grated 31P NMR spectra of the reaction mixture,
two products were identified: diethyl phosphorami-
date (4a), δ 10.5 ppm, and N,Nꢀ-bis(diethyl phos-
phor)sulfamide (3a). After crystallization from chlo-
roform/petroleum ether (bp 40–60◦C), 0.068 g (94%
yield) of pure 3a was isolated.
m/z = 469.0, [M(3b) − H + 2Na]+; 6c, m/z = 444.1,
[M(3c) − H + 2Na]+ were detected.
Reaction of N-Sulfinylphosphoramidate 1a with
Diisopropyl Phosphoramidate (4b)
A mixture of 0.063 g (0.34 mmol) of 4b and
0.069 g (0.34 mmol) of 1a, dissolved in 5 mL of
dry dichloromethane, was stirred for 4 h at room
temperature. After this time in 31P spectra of the
reaction solution, the lines of diethyl phospho-
ramidate (4a) at δ 9.7 ppm and diisopropyl phos-
phor N-sulfinylamidate (1b) at δ −12.8 ppm were
observed.
Reaction of N-Sulfinylphosphoramidate 1a
with Iodoxybenzene (5) and Diisopropyl
Phosphoramidate (4b)
Dry 5, 0.14 g (0.59 mmol), was added in one portion
to a stirred solution of 0.215 g (1.18 mmol) ami-
date 4b and 0.235 g (1.18 mmol) of 1a in 8 mL
dichloromethane, under argon at the temperature
20◦C. The reaction mixture was stirred at room tem-
perature for 24 h, and after this time the reaction
solution was analyzed by 31P NMR. The integrated
spectra showed formation of four products identified
as N,Nꢀ-bis(diethyl phosphor) sulfamide (3a), δ −5.9
ppm (20% yield); N,Nꢀ-bis(diisopropyl phosphor)
sulfamide (3b), δ −7.9 ppm (14% yield); N-[O,O-
diethyl] Nꢀ-[O,O-diisopropyl phosphor] sulfamide
(3c), δ −5.7 ppm and −8.1 ppm (34% yield); diethyl
phosphor amidate (4a), δ 9.6 ppm (32% yield). The
analysis of MS FAB spectra of this mixture showed
the presence of lines ascribed to all identified prod-
uct of the reaction: 3a, m/z = 367.1, [M − 1]; 3b,
m/z = 423.2 [M − 1]; 3c, m/z = 395.1 [M − 1]; 4a,
m/z = 154 [M + 1].
Reaction of Diisopropyl Phosphoramidate (4b)
with Thionyl Chloride
A solution of 2.28 g (12.5 mmol) of amidate 4b
and 1.49 g (12.5 mmol) of freshly distilled thionyl
chloride in 20 mL of benzene was heated un-
der reflux for 6 h. The solvent was removed in
vacuo. After the distillation, 2.1 g (74%) of oily
liquid reaction product, identified as a diisopropyl
N-sulfinylphosphoramidate (1b), was obtained: bp
84oC/0.8 mmHg; 1H NMR, δ 1.37 ppm (dd, 12H,
(CH3)2CH ), 4.88 (m, 2H, (CH3)2CH ); 31P NMR δ
−12.4 ppm.
Reaction of 1a with Cumene Peroxide (8) in the
Presence of 2,2-Dimethyl-propan-1-ol (9)
To the solution of 1 g (5.0 mmol) N-sulfinylphos-
phoramidate 1a in dry dichloromethane, 1.37 g
(5.0 mmol) of cumyl peroxide (8) in 10 mL anhy-
drous dichloromethane was added at −50◦C. The
stirring was continued for 2 h and then the tempera-
ture was increased slowly for 40 min to −20◦C. Then
0.44 g (5.0 mmol) of 2,2-dimethyl-propan-1-ol (9) in
5 mL of dichloromethane was added, and reaction
mixture was stirred at this temperature for next 2 h.
The solvent was removed in vacuo, and in the 31P
NMR spectra of the crude reaction mixture signals
at δ −2.36 ppm (44%) and 9.7 ppm (56%) were
observed. The first one we identified as a character-
istic for diethyl phosphor N-(2,2-dimethylpropyl)
sulfamate (10a), and the second one was ascribed
to amidate 4a. In the MS FAB spectra, lines of
the mass m/z 154 [M + 1] 4a, and m/z 302 [M − 1]
10a, were observed. The attempt to isolate the ester
10a by rapid column chromatography (petroleum
ether (bp 40–60◦C):acetone:chloroform) was
unsuccessful.
Interaction of the Crude Mixture of the Products
3a, 3b, 3c, and 4a
With Pyridine. To a stirred sample 0.1 g of a
mixture 3a, 3b, 3c, and 4a dissolved in 5 mL of
dry dichloromethane, 1 mL of pyridine was added
at room temperature. In the 31P NMR spectra of this
solution, the presence of signals ascribed to the pyri-
dinium salts of starting sulfamides was observed δ:
−4.6, −2.1 ppm, 3c; −4.2 ppm, 3b; −2.5 ppm, 3a.
31
The resonance signal at δ of 4a was unchanged.
With Sodium Chloride. To the sample of 0.1 g
mixture of products 3a, 3b, 3c, and 4a in 3 mL
dry dichloromethane, 0.05 g of sodium chloride
was added. The solvent was evaporated, and oily
liquid material was obtained and analyzed by
MS FAB spectrometry. In their positive ion spec-
tra, three lines of mass characteristic for clus-
ters ions: 6a, m/z = 413.2, [M(3a) − H + 2Na]+; 6b,
Heteroatom Chemistry DOI 10.1002/hc

Oxidation of Diethyl N-Sulfinylphosphoramidates 535
N,Nꢀ-bis(diisopropyl phosphor) sulfamide (3b) was
stirred in 5 mL of dry dichloromethane at room tem-
perature. After 24 h in the 31P NMR spectra of this
solution mixture, only the presence of signals at δ
−5.7 and −7.5 ppm, characteristic for starting sul-
famides, was observed.
Reaction of 1a with 5 and
9-Phenylfluorenol (11)
To the suspension of 0.17 g (0.72 mmol) dry io-
doxybenzene (5) and 0.37 g (1.43 mmol) of 11 in
10 mL dry dichloromethane, 0.285 g (1.43 mmol)
of diethyl N-sulfinylphosphoramidate (1a), under
argon at −30◦C, was added. After 3 h, the temper-
ature was slowly increased to 20◦C, and the stir-
ring was continued for next 3 h. The solvent was
removed in vacuo, and obtained products were sepa-
rated by column chromatography on silica gel (chlo-
roform:hexane:ethyl acetate 3:1:1); 0.34 g (59%) of
O,O-diethyl phosphor N-9-phenylfluorenol amidate
(12), 1H NMR δ 0.95 (t, 6H, OCH2CH3), 3.53 (q, 2H,
OCH2CH3), 3.68 (q, 2H, OCH2CH3), 3.86 (d, 1H,
NH), 7.25 (m, 6H, Ph), 7.36 (m, 6H, Ph), 7.66 (d, 1H,
Ph), 31P NMR δ5.1, MS FAB m/z 394.3[M + 1]; 0.16
g (31%) N,Nꢀ-bis(diethyl phosphor) sulfamide (3a),
31P δ −6.1, MS FAB m/z 367.2 [M − 1]; 0.02 g (11%)
diethyl phosphoramidate (4a), 31P NMR δ 9.6, MS
FAB m/z 154.0 [M + 1].
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Heteroatom Chemistry DOI 10.1002/hc

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Heteroatom Chemistry DOI 10.1002/hc