Phosphorylation of 3,4-dichloro-5-hydroxy-2(5H)-furanone with tributylphosphine

Article abstract of DOI:10.1023/A:1020863326072

The reaction of 3,4-dichloro-5-hydroxy-2(5H)-furanone with 2 mol of tributylphosphine involves substitution of both chlorine atoms to form an unstable diphosphonium salt. The latter undergoes partial hydrolysis with cleavage of one of the P-C bonds, yield

Full text of DOI:10.1023/A:1020863326072

Russian Journal of General Chemistry, Vol. 72, No. 8, 2002, pp. 1202 1206. Translated from Zhurnal Obshchei Khimii, Vol. 72, No. 8, 2002,
pp. 1283 1287.
Original Russian Text Copyright
2002 by Polezhaeva, Volodina, Kalinina, Sahibullina, Chmutova, Galkin, Cherkasov.
Phosphorylation of 3,4-Dichloro-5-hydroxy-2(5H)-furanone
with Tributylphosphine
N. A. Polezhaeva, Yu. M. Volodina, I. V. Kalinina, V. G. Sahibullina,
G. A. Chmutova, V. I. Galkin, and R. A. Cherkasov
Kazan State University, Kazan, Tatarstan, Russia
Received November 3, 2000
Abstract The reaction of 3,4-dichloro-5-hydroxy-2(5H)-furanone with 2 mol of tributylphosphine involves
substitution of both chlorine atoms to form an unstable diphosphonium salt. The latter undergoes partial
hydrolysis with cleavage of one of the P C bonds, yielding finally a monophosphorylation product. A pro-
bable reaction pathway is considered in terms of quantum chemistry.
Our previous studies on phosphorylation of 3,4-di-
lithium diphenylphosphide with a mucochloric acid
chloro-5-hydroxy-2(5H)-furanone (mucochloric acid) ester [5].
(I) with phosphites, phosphines, and other trivalent
phosphorus derivatives established that the reaction
direction and the structure and composition of the re-
action products much depend on the nature of sub-
stituents on the 3-P atom [1]. This method of phos-
phorylation of halocyclenes allowed preparation of
various 4- and 5-monophosphorylation products, such
as oxofurylphosphonates, phosphonium salts, and
phosphabetaines [2 4]. Attempted substitutions of
both chlorine atoms in mucochloric acid most fre-
quenly failed: Diphosphorylation products could not
be isolated pure. Only one diphosphorylated furanone
Triphenylphosphine reacts with mucochloric acid
(I) to give phosphonium salt II whose structure was
established by X-ray diffraction analysis [3, 4]. All
attempts to obtain a diphosphorylation product by
treatment of the monophosphonium salt with a second
triphenylphosphine molecule or by reaction of fura-
none II with two mol of triphenylphosphine led to
formation of two products by two concurrent path-
ways. One of them, II
III, is equilibrium formation
of diphosphonium salt III which, however, could not
be isolated pure because of the easy convertion to
derivative was described, prepared by the reaction of monophosphorylation product II. The same result was
obtained for the reaction of furanone I with two mol
O
O
of triphenylphosphine. Besides, the second mole of
triphenylphosphine can act as a base and effect de-
hydrochlorination of monophosphonium salt II
to betaine IV.
Cl
Ph2P
O
O + 2Ph2PLi
OR
Cl
Ph2P
OR
H
H
Scheme 1.
O
O
O
Cl
Cl
Cl
Cl
O + Ph3P
O
O
+
+
Ph3P HCl
Ph3P
Ph3P
CHOH
CHOH
II
CHO
IV
Cl
I
+ Ph3P
Cl
O
+
Ph3P
O
CHOH
III
+
I + 2Ph3P
Ph3P
Cl
1070-3632/02/7208-1202$27.00 2002 MAIK Nauka/Interperiodica

PHOSPHORYLATION OF 3,4-DICHLORO-5-HYDROXY-2(5H)-FURANONE
1203
In the present work we studied the possibility of
synthesis of a diphosphonium salt by reaction of
furanone I with tributylphosphine, a more nucleo-
philic 3-P derivative than triphenylphosphine. The
phosphorylating power of tributylphosphine was pre-
viously demonstrated on an example of another halo-
cyclane, 2-N-phenyl-4,5-dichloropyridazinone [6].
liquor was examined by spectral methods. In its IR
spectrum, instead of the disappeared bands at 1800 and
1650 cm related to the C=O and C=C groups of the
1
furan ring, a broad strong band was observed at 1620
1
1640 cm , which, according to [3], can be assigned
to vibrations of phosphabetaine system VI. It is not
be excluded that the phosphabetaine exists in equilib-
rium with phosphorane VII, as evidenced by the
It was found that the reaction of Bu3P with fura-
none I in a 1:1 ratio gives [3-chloro-2,5-dihydro-5-
hydroxy-2-oxofuran-4-yl]tributylphosphonium chlo-
appearance of a weak singlet signal at
5.8 ppm in
the phosphorane region. The quantum-Pchemical cal-
culations showed that phosphabetaine VI is more
stable than phosphorane VII. The enthalpies of
formation of these structures are 140.6 and
129.1 kcal/mol, respectively.
ride (V) as a viscous undistillable liquid,
64.4 ppm
P
(Scheme 2). The IR spectrum of the product contains
1
absorption bands at 1800 (C=O) and 1650 cm
(C=C). The presence of the chloride ion was proved
by the formation of an AgCl precipitate on treatment
with an AgNO3 solution. The 1H NMR spectrum
contains a group of signals belonging to the (C4H9)3P
group, as well as signals at 3.75 s (OH) and 4.1 ppm
The reaction of two mol of Bu3P with mucochloric
acid I in chloroform was accompanied by appearance
of two strong doublets at
37.5 and 42.2 ppm (3JPP
P
11 Hz), implying formation of diphosphoniofuranone
VIII. All attempts to isolate this product pure failed.
3
(CH; JPH 9 Hz).
Quantum-chemical calculations (PM3 method) of
the enthalpies of formation of the monophosphonium
salts which can be formed by phosphorylation of fu-
ranone I with tributylphosphine gave evidence to
show that -phosphorylated furanone Va is slightly
more favorable than the alternative, -phosphorylation
product Vb.
Nevertheless, this reaction in ether resulted in isola-
tion of a white crystalline compound (mp 165 167 C
after recrystallization in air;
36.6 ppm). It was
P
identified as tributyl(2,5-dihydro-4,5-dihydroxy-2-
oxofuran-3-yl)phosphonium chloride (IX). The ob-
servation in its IR spectrum of strong bands at 1690
1
(C=O) and 1620 cm (C=C), as well as a broad
1
diffuse band at 2250 2400 cm belonging to the
+
O
O
hydroxy group involved in a strong hydrogen bond
with the chloride ion confirms the proposed structure.
The formation of such an H complex we reported pre-
viously [6].
Bu3P
Cl
Cl
O
O
+
Cl
Bu3P
OH
OH
Vb
Hf 177 kcal/mol
H
H
Cl
Va
The formation of furanone IX is best explained by
a scheme offered for the formation of a structurally
structure phosphonium salt obtained from tributyl-
phosphine and 2-N-phenyl-4,5-dichloropyridazone [6]
(Scheme 3, all H0f values are in kcal/mol).
Hf 179 kcal/mol
These data strongly suggest that the phosphine
3-P atom is quaternized by substitution of the
chlorine atom on C4 rather than on C3, which was
earlier observed in all reactions of 3-P derivatives
with mucochloric acid [2, 3].
According to this scheme, the first stage of the re-
action of furanone I with a twofold excess of Bu3P
involves substitution of two chlorine atoms to form
an unstable diphosphonium intermediate VIII. During
workup of the reaction mixture, partial hydrolysis
with atmospheric moisture occurs, accompanied by
P C4 bond cleavage and formation of a stable final
Treatment of monophosphorylated furanone V with
triethylamine caused separaion of triethylamine
hydrochloride. It was filtered off, and the mother
Scheme 2.
O
O
O
Cl
Cl
Et3N
Cl
I + Bu3P
O
O
O
Et3N HCl
+
+
Bu3P
Bu3P
OH
H
O
H
Bu3P
Cl
O
V
VI
VII
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 72 No. 8 2002

1204
POLEZHAEVA et al.
Scheme 3.
+
O
Bu3P
Cl
I
+
2Bu3P
Hf0 68.35
O
+
Hf0 122.2
Bu3P
OH
H
Cl
VIII
Hf0 241.9
O
+
+ Cl
Bu3P
O
O
Bu3P
H2O
Bu3P
C
C
H
O
O
O
HCl
HCl, Bu3P=O
O
OH
HO
O
OH
OH
H
H
O
Hf0 209.3
X
IX
Hf0 227.0
H2O
H2O
C4H9
Bu2P(O)
HO
O
OH
H
XI
Hf0 236.1
product IX. The preferred cleavage of the P C4 bond
which is in the position to the carbonyl group was
confirmed by the reaction of 2-N-phenyl-4,5-dichloro-
pyridazone with tributylphosphine. The structure of
the product was established by X-ray diffraction [6].
Analogous process is likely to occur with diphos-
phonium salt VIII.
structures presented in Scheme 3 we could evaluate,
in terms of enthalpy, the probability of separate stages.
Thus, the first stage, that is formation of diphospho-
rylation product VIII, is thermodynamically un-
favorable ( Hf +83.87 kcal/mol); this stage is pro-
bably driven by solvation effects which were not con-
sidered in the calculations. At the same time, hydro-
lysis of product VIII with HCl evolution and tributyl-
phosphine oxide formation (the latter can also be
formed by oxidation of the starting Bu3P with atmos-
pheric oxygen) yields product IX which is thermo-
If the reaction of furanone I with two moles of
Bu3P was carried out under argon, then, along with
salt X, a product with
77 ppm and tributylphos-
phine oxide ( 43 ppm)Pcould be isolated from the
P
dynamically favorable
(
Hf
20.51 kcal/mol).
mother liquor [7]. The product with
77 ppm was
assigned the structure of betaine (ylide) PX. Its IR spec-
Subsequent dehydrochlorination of phosphonium salt
IX to form betaine (ylide) X ( Hf 2.80 kcal/mol) is
also favorable. Analysis of the structure of this inter-
mediate points to a considerable delocalization of
electron density in this molecule. The charge distribu-
tion can be presented as follows:
trum contained two strong C=O bands (1800 and
1
1
1770 cm ) and a C=C band at 1620 cm .
The formation of monophosphorylated dihydroxy-
furanone IX and its dehydrochlorination product X
can also explained in terms of Scheme 3. The forma-
tion of a phosphine oxide was previously observed in
the reaction of triphenylphosphine with mucochloric
acid while recrystallization of a phosphabetaine [4].
The dehydrochlorination of a phosphonium salt
(analogous to IX) and the formation of a stable
betaine (ylide) was also previously observed in reac-
tions of similar pyridazinone derivatives [8].
Ob
+
qP +1.819
Bu3P
qa 0.392
qb 0.423
O
Oa
OH
H
Evidently, inspite of the strong difference in the
reactivity of halogen-containing
carbonyl O- and N-containing heterocyclic com-
, -unsaturated
By PM3 quantum-chemical calculations of various
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 72 No. 8 2002

PHOSPHORYLATION OF 3,4-DICHLORO-5-HYDROXY-2(5H)-FURANONE
1205
pounds: 3,4-dichloro-5-hydroxy-2(5H)-furanone and
2-N-phenyl-4,5-dichloro-3-pyridazinone, especially
tered off, and the filtrate was studied spectroscopically;
5.8 ppm.
P
toward P-nucleophiles [6, 8], furanones and pyrida-
zinones react with tributylphosphine, as well as with
lithium diphenylphosphide [9], in a principally similar
way.
Reaction of 3,4-dichloro-5-hydroxy-2(5H)-
furanone with tributylphosphine in a 1:2 ratio.
Tributylphosphine, 5.75 g, was added dropwise with
constant stirring to 2.37 g of mucochloric acid in 30
ml of ether. The solvent was removed in part, a white
To obtain experimental evidence for this reaction
pathway, we reacted mucochloric acid with 2 mol of precipitate formed and was filtered off and washed
tributylphosphine and treated the reaction mixture
with water. This caused not only P C4 bond cleavage
but also hydrolysis of phosphonium salt IX (or
betaine X) with formation of phosphine oxide XI
with ether. mp 165 167 C; P 36.6 ppm. IR specrrum,
, cm : 1690 (C=O), 1620 (C=C), 2250 2400 (OH).
1
Reaction of 3,4-dichloro-5-hydroxy-2(5H)-
furanone with tributylphosphine (1:2) and water.
Tributylphosphine, 5.75 g, was added dropwise with
constant stirring to 2.37 g of mucochloric acid. Then
20 ml of water was added, and the resulting mixture
was thoroughly stirred. The chloroform layer was
separated, and the solvent was removed by distillation
to leave a viscous dark oil, from which crystals pre-
(Scheme 3),
54 ppm. The IR spectrum of the
P
product contains bands at 1780 (C=O), 1620 (C=C),
1
1220 (P=O), and 2600 2800 cm (OH strongly
hydrogen-bonded with P=O). It is known [10] that the
tendency of one or another group to cleave on hydro-
lysis of phosphonium salts depends on the nature of
all groups surrounding the phosphorus atom. In the
case in hand, hydrolysis is evidently accompanied by
cleavage of not only the electron-acceptor oxofuranyl-
cipitated on standing and again liquefied in air,
54 ppm. IR spectrum, , cm : 1780 (C=O), 1620
P
1
phosphonium group by the pathway VIII
IX, as is
(C=C), 1220 (P=O), 2600 2800 (OH).
usually observed in nucleophilic substitutions at the
phosphonium center, but also of one butyl group,
which leads to formation of phosphine oxide XI. Such
scheme of hydrolysis of the phosphorylation products
of 2-N-phenyl-4,5-dichloropyridazone was described
by us previously [6].
ACKNOWLEDGMENTS
The work was financially supported by the Russian
Foundation for Basic Research (project no. 99-03-
32880).
EXPERIMENTAL
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P
1
1
3
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