β-(N-acylamino)vinylphosphonium salts - Synthesis and properties

Article abstract of DOI:10.1080/10426500214561

A reaction of β-carbonyl phosphorus ylides with imidoyl halides gives hitherto unknown β-(N-acylamino)vinylphosphonium salts. The same product can be obtained using the N-monosubtituted amide/Ph₃PBr₂/Et₃N system instead of imidoyl halide. The key step of the reaction probably involves an intramolecular [1,3] O-to-N migration of the vinyl group, converting the primary O-imidoylation product into β-(N-acylamino)vinylphosphonium salt.

Full text of DOI:10.1080/10426500214561

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
β-( N -Acylamino)vinylphosphonium Salts--
Synthesis and Properties
Roman Mazurkiewicz , Beata Fryczkowska , Rafał Gabański , Roman
Luboradzki , Andrzej Włochowicz & Wojciech Mól
To cite this article: Roman Mazurkiewicz , Beata Fryczkowska , Rafał Gabański , Roman
Luboradzki , Andrzej Włochowicz & Wojciech Mól (2002) β-( N -Acylamino)vinylphosphonium
Salts--Synthesis and Properties, Phosphorus, Sulfur, and Silicon and the Related Elements,
177:11, 2589-2598, DOI: 10.1080/10426500214561
To link to this article: http://dx.doi.org/10.1080/10426500214561
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Phosphorus, Sulfur and Silicon, 2002, Vol. 177:2589–2598
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Copyright 2002 Taylor & Francis
1042-6507/02 $12.00 + .00
DOI: 10.1080/10426500290110801
-(N-ACYLAMINO)VINYLPHOSPHONIUM
SALTS—SYNTHESIS AND PROPERTIES
Roman Mazurkiewicz,a Beata Fryczkowska,b Rafal Gaban´ski,a
Roman Luboradzki,c Andrzej Wlochowicz,b and Wojciech Mo´la
Institute of Organic Chemistry and Technology, The Silesian
University of Technology, Poland;a Department of Textile
Engineering and Environmental Sciences,
The Technical-Humanistic Academy, Poland;b and Institute
of Physical Chemistry, Polish Academy of Sciences, Polandc
(Received February 19, 2002; accepted February 21, 2002)
A reaction of -carbonyl phosphorus ylides with imidoyl halides
gives hitherto unknown -( N-acylamino)vinylphosphonium salts.
The same product can be obtained using the N-monosubtituted
amide/Ph3PBr2/Et3 N system instead of imidoyl halide. The key step
of the reaction probably involves an intramolecular [1,3] O-to-N migra-
tion of the vinyl group, converting the primary O-imidoylation product
into -( N-acylamino)vinylphosphonium salt.
Keywords:
-Carbonyl ylides;
-(N-acylamino)vinylphosphonium
salts; imidoylation; imidoyl halides; N-monosubstituted amide/
Ph3PBr2/Et3N system; rearrangement
INTRODUCTION
Vinylphosphonium salts 1 have been attracting significant attention of
synthetic chemists since 1964, when Schweizer1 realized that the addi-
tion of nucleophiles with a carbonyl function to vinylphosphonium salts
results in phosphorus ylides 2, which can undergo the intramolecular
Wittig reaction (Scheme 1). Many carbo- and heterocyclic systems have
been synthesized in this way.2
Recently, we have preliminarily communicated the synthesis
of hitherto unknown -(N-acylamino)vinylphosphonium salts 7 by
imidoylation of -carbonyl phosphorus ylides 4 with imidoyl halides
Address correspondence to Roman Mazurkiewicz, Institute of Organic Chemistry and
Technology, The Silesian University of Technology, Krzywoustego 4, Gliwice, PL-44-100,
Poland. E-mail: romanm@zeus.polsl.gliwice.pl
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R. Mazurkiewicz et al.
SCHEME 1
5 (Scheme 2).3 In this article we give a full account concerning this syn-
thesis, including some novel modification of it, which consists in using
the N-monosubtituted amide/Ph3PBr2/Et3N system instead of imidoyl
halide.
RESULTS AND DISCUSSION
The treatment of the -corbonyl phosphorus ylide with an imidoyl
halide in acetonitrile at room temperature for 24 h results in -(N-
acylamino)vinylphosphonium salts 7 as stable, usually crystalline com-
pounds in good yields (procedure A and B, Scheme 2, X = Cl or I). Imi-
doyl iodides were prepared in situ from imidoyl chlorides by exchange
of chlorine with NaI. The obtained vinylphosphonium salts can be pre-
cipitated from the reaction mixture with Et2O and purified further, if
necessary, by crystallization from a mixture of MeCN or CH2Cl2 with
Et2O or by column chromatography.
SCHEME 2
The preparation of imidoyl halides is rather labor consuming. Apart
from that, imidoyl halides, being highly reactive substances, must of-
ten be prepared as required, some of them tending to undergo self-
condensation.4 Taking into account these disadvantages, we tried to
use the N-monosubtituted amide/Ph3PBr2/Et3N system as a source of
an imidoylating agent generated in situ. In 1990 we provided some
spectral evidence, that the new imidoylating agent generated from
N-monosubtituted amides and Ph3PBr2 in the presence of Et3N had the
structure of N,N,N,N0-tetrasubstituted amidinium salts 9, and could be
detected based on a characteristic strong
N absorption band at about
C

-( N-Acylamino)vinylphosphonium Salts
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SCHEME 3
1
1700 cm (Scheme 3).5 N,N,N,N0-Tetrasubstituted amidinium salts 9
can remain in equilibrium with imidoyl bromide 8; both of these com-
pounds can act as an effective imidoylating agent.
As had been expected, the treatment of -carbonyl phosphorus ylides
with the N-monosubtituted amide/Ph3PBr2/Et3N system in CH2Cl2 at
room temperature for 24 h gives -(N-acylamino)vinylphosphonium
bromides 7, usually in good yields (procedure C) (Table I). Before adding
an ylide, in all the cases we detected in the reaction mixture a strong
absorption band of the imidoylating agent at about 1700 cm 1, as
well as the characteristic set of absorption bands of triphenylphos-
phine oxide at 1439, 1191, and 1120 cm 1, the intensity of which
approximately corresponds to the total conversion of Ph3PBr2 into
Ph3PO.
The structures of the -(N-acylamino)vinylphosphonium salts were
confirmed by their spectroscopic properties (IR, 1H-, and 13C-NMR) and
satisfactory elemental analyses (Table II), as well as, in the case of
the compound 7e, by a single crystal X-ray structure determination,
which revealed its Z-configuration (Figure 1). The crystallographic data
(excluding structure factors) for the structure 7e have been deposited
with the Cambridge Crystallographic Data Center as a supplementary
publication number CCDC 166899. In the case of compounds 7a and 7d,
the magnitude of the JH H coupling constants at the double bond (14.7–
15.3 Hz) suggests rather an E-configuration of the salts. In the case of
compound 7g we have obtained evidently a mixture of two possible
stereoisomers.
It is obvious, that the final reaction product 7 cannot be formed in
a simple, direct way from ylide 4 and imidoyl halide 5. In order to ex-
plain our results we assume this reaction to involve the O-imidoylated
intermediate 6 and the [1,3] O-to-N sigmatropic migration of its vinyl
group. A similar kind of [1,3] sigmatropic migrations is well-known
in the literature;6 e.g., O-imidoylated carboxamides undergo a similar
rearrangement.5,7 An analogous rearrangement probably also takes
place in the case of the similar, well-known acylation of -carbonyl

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R. Mazurkiewicz et al.
FIGURE 1 ORTEP-Plot of the -(N-benzoylamino)- -methylvinyltripheny-
phosphonium chloride 7e.
ylides; however, being a degenerate rearrangement, it cannot be directly
observed.
CONCLUDING REMARKS
The reported reactions offer a convenient way for the synthesis of
-
(N-acyloamino)vinylphosphonium salts. The phosphonium salts 7 can
be considered to be prospective precursors for the synthesis of amino
derivatives of carbo- and heterocyclic systems (see Scheme 1), and some
important reagents for organic synthesis like N-acylynamines8 (by
-
elimination of Ph3P and HX if R2 = H) or N-vinylamides (by hydro-de-
phosphoniation of phosphonium salts 7).
EXPERIMENTAL
General
M.p.s, determined in capillary tubes, are uncorrected. IR spectra were
recorded on a Zeiss Specord M 80 spectrophotometer; the measure-
ments were carried out in CHCl3 (0.2 M) using cells of 0.105 mm.
1H and 13C NMR spectra were recorded in CDCl3 on a Varian UNITY

-( N-Acylamino)vinylphosphonium Salts
2597
INOVA-300 spectrometer at operating frequencies of 300 and 75.5 MHz,
respectively, in the FT mode using TMS as an internal standard.
Starting Materials
Commercial grade acetonitrile and CH2Cl2 were distilled and dried
over molecular sieves 4A. The following reagents were of com-
mercial quality (Aldrich): (triphenylphosphoranylidene)acetaldehyde,
1-(triphenylphosphoranylidene)-2-propanone and 2-(triphenylphos-
phoranylidene)propionaldehyde. The synthesis and properties of the
following compounds have been reported in the literature: N-phenyl-
acetimidoyl chloride,9 N-methylbenzimidoyl chloride,10 N-benzyl-
benzimidoyl chloride,11 and N-phenylbenzimidoyl chloride.12
Synthesis of -(N-Acyloamino)vinylphosphonium
Chlorides 7 Using Imidoyl Chlorides
(General Procedure A)
To a solution of imidoyl halide 5 (2.4 mmol) in MeCN (3.6 ml) ylide 4
(2 mmol) was added and the mixture was left at room temperature for
24 h. The phosphonium salt was precipitated from the reaction mixture
with Et2O (5–8 ml). The product can be purified further, if necessary, by
column chromatography on silica gel eluting with a mixture of CH2Cl2
and MeOH (97:3 or 99:1, v/v). Crude 7 can usually be recrystallized
by dissolving in acetonitrile or CH2Cl2 and precipitating with diethyl
ether (1:1–1:2; v/v).
Synthesis of -(N-Acyloamino)vinylphosphonium
Iodides 7 Using Imidoyl Chlorides
(General Procedure B)
To a solution of imidoyl halide 5 (2.4 mmol) in MeCN (3.6 ml) NaI
(0.30 g, 2 mmol) and ylide 4 (2 mmol) was added and the mixture was
left at room temperature for 24 h. The precipitated NaCl was filtered
off and the phosphonium salt was isolated from the reaction mixture
as described above (procedure A).
Synthesis of -(N-Acyloamino)vinylphosphonium
Bromides 7 Using the N-monosubstituted
Amide/Ph3PBr2/Et3N System (General Procedure C)
To a solution of triphenylphosphine (0.63 g, 2.4 mmol) in CH2Cl2
(8 ml) a solution of bromine (0.38 g, 2.4 mmol) in CH2Cl2 (1 ml) was
added at room temperature under argon atmosphere. After 30 min Et3N
(0.85 ml, 6 mmol) and amide (2.2 mmol) was added. After next 30 min
ylide (2 mmol) was added and the mixture was left at room temperature

2598
R. Mazurkiewicz et al.
for 24 h. The solvent was evaporated and the phosphonium salt was iso-
lated from the reaction mixture by column chromatography as described
above (procedure A).
REFERENCES
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Chem. Commun., 92 (1965); E. E. Schweizer and G. J. O’Neill, J. Org. Chem., 30,
2082 (1965).
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Starzewski, and D. A. Dixon, Ylides and Imines of Phosphorus (Wiley, New York,
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(2002).
[4] R. Bunnet, In The Chemistry of the Carbon-Nitrogen Double Bond, edited by S. Patai
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