Synthesis of substituted 4,5,8,7-tetrafluorobenzo[d]-λ5- phospholes

Article abstract of DOI:10.1023/B:RUGC.0000025498.95833.35

The reactions of diethyl pentafluorophenylphosphonite and ethyl bis(pentafluorophenyl)phosphinite with activated alkynes proceed as two-stage cycloaddition processes and lead to formation of sufficiently stable heterocyclic fused fluorophosphoranes. Hydro

Full text of DOI:10.1023/B:RUGC.0000025498.95833.35

Russian Journal of General Chemistry, Vol. 74, No. 2, 2004, pp. 189 192. Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 2, 2004,
pp. 214 218.
Original Russian Text Copyright
2004 by Trishin, Namestnikov, Bel’skii.
Synthesis of Substituted
5
4,5,8,7-Tetrafluorobenzo[d]- -phospholes
Yu. G. Trishin, V. I. Namestnikov, and V. K. Bel’skii
St. Petersburg State Technological University of Plant Polymers, St. Petersburg, Russia
Received December 27, 2002
Abstract The reactions of diethyl pentafluorophenylphosphonite and ethyl bis(pentafluorophenyl)phos-
phinite with activated alkynes proceed as two-stage cycloaddition processes and lead to formation of suffi-
ciently stable heterocyclic fused fluorophosphoranes. Hydrolysis of the latter is accompanied by cleavage of
the exocyclic P O bond and formation of substituted 4,5,6,7-tetrafluorobenzo[d]- 5-phospholes, previously
uknown bicyclic phosphorus-containing compounds.
Over the last few years we have studied applicability
of the principle of two-stage cycloaddition of , -
unsaturated P(III) derivatives to reagents containing
electrophilic and nucleophilic reaction centers in the
1,3 or 1,2 positions [1] for preparing phosphorus-
containing heterocycles on the basis of ortho-halo-
phenyl P(III) derivatives. In detail, we have shown
[2 5] that in reactions with nitrilimines (Housgen
1,3-dipoles) these compounds behave as structural and
electronic analogs of -halo-substituted alkenyl P(III)
derivatives. Hence, in reactions of diethyl o-chloro-
and o-bromophenylphosphonous acids with C,N-di-
arylnitrilimines generated from corresponding 1,3-di-
aryltetrazoles at 170 C, nucleophilic attack of phos-
phorus on the nitrilimine carbenium atom results in
initial formation of a P+C=N N betaine, followed by
heteroring closure as a result of intramolecular
nucleophilic substitution of halogen located in the
benzene ring ortho to the phosphonium group. Sub-
sequent dealkylation of the ethoxy radical on phos-
phorus under the action of substituted chloride or
bromide ions leads to formation of 1,4-dihydro-5,6,
7,8-tetrafluorobenzo[e]-1,2,4 5-diazaphosphorine
4-oxide derivatives [2]. Diethyl pentafluorophenyl-
phosphonite reacts with nitrilimines in a similar way.
Here cyclization proceeds under milder conditions,
and nitrilimines are generated from the corresponding
dihalohydrazones under the action of triethylamine [3].
In the reactions of bis(pentafluorophenyl)phenylphos-
phine and (pentafluorophenyl)diphenylphosphine, i.e.
compounds containing no ethoxy groups on phos-
phorus, the first two stages, too, involved formation
of a P+C=N N betaine and intramolecular cyclization.
However, here, the ring formation and expulsion of
fluorine from the ortho position give rise to fairly
stable fluorophosphoranes [4, 5]. Hydrolysis of the
latter involves cleavage of bonds of the five-co-
ordinate phosphorus atom and yields both open-chain
and cyclic final products.
In this work we have studied reactions of diethyl
pentafluorophenylphosphonite (I) and ethyl bis(penta-
fluorophenyl)phosphinite (II) with activated alkynes.
It is known [1] that the latter react with -halo-sub-
stituted ethylene P(III) derivatives similarly to nitril-
imines to form cycloaddition products. We found that
pentafluorophenyl P(III) derivatives I, II react with
dimethyl acetylenedicarboxylate, as well as methyl
ester and nitrile of phenylpropiolic acid to form fluoro-
phosphoranes IIIb VIb. These reactions are two-
stage processes and probably begin with nucleophilic
attack of P(III) on the nitrilimine carbenium center to
give dipolar ions IIa VIa. After that, heteroring
closure occurs through intramolecular nucleophilic
aromatic substitution of fluorine located ortho to the
phosphonium group. The fluoride ion expelled takes
part in formation of fluorophosphoranes IIIb VIb
which are colored oils (from light to dark brown)
gradually solidifying on handling. Fluorophospho-
ranes IIIb VIb are sufficiently stable at 20 C in the
absence of air moisture. They are readily soluble in
ether. The 31P NMR spectra of IIIb VIb contain an
upfield doublet with a chemical shift characteristic of
P(V) compounds,
49.4 to 53.8 ppm (1JPF 795
P
833 Hz). In air the fluorophosphoranes undergo
hydrolysis with HF evolution, giving hydroxyphos-
phoranes IIIc VIc as intermediates. Finally, alcohol
is evolved to form substituted 4,5,6,7-tetrafluoro-
5
benzo[d]- -phospholes III VI.
Heterocycles III VI are crystalline substances.
They are readily soluble in acetone, chloroform,
DMSO, benzene, moderately soluble in ether, and
1070-3632/04/7402-0189 2004 MAIK Nauka/Interperiodica

190
TRISHIN et al.
F
F
F
F
F
F
F
F
F
EtO
R1
P
+ R2 C C R3
F
F
F
F
F
P
C
+
P
EtO
R1
EtO
R1
R2
F
C=C R3
C
I, II
R2
R3
IIIa VIa
IIIb VIb
F
F
F
F
F
H2O
HF
F
F
F
EtOH
HO
EtO
P
O
P
C
R1
R2
R1
R2
C
C
C
R3
R3
IIIa VIc
III VI
III, R1 = EtO, R2 = R3 = MeOC(O); IV, R1 = EtO, R2 = Ph, R3 = CN; V, R1 = EtO, R2 = Ph, R3 = MeOC(O); VI, R1 =
C6F5, R2 = R3 = MeOC(O).
insoluble in hexane. Their cyclic structure was
It was found all atoms of the bicyclic system are
coplanar within 0.012 , except for phosphorus which
deviates from the bicycle plane by 0.068 . Therefore,
the bicycle can be considered almost planar. The angle
between the bicycle and pentafluorophenyl planes is
92.8 . The MeOC16O group is at an angle of 11.3 to
the bicycle plane, while the MeOC14O group is almost
perpendicular to it (93.6 ). The tetrahedral configura-
tion of phosphorus is strongly distorted, because the
X P X angles vary in the range 91.0 118.8 .
confirmed by the
values: 30.7 35.9 ppm for com-
pounds III V withPR1=EtO and 16.0 ppm for com-
pound VI with R1=Ph. The H NMR spectra of phos-
1
pholes III VI contain expected signals of the R1, R2,
and R3 groups. The IR spectra lack C C absorption
and contain absorption bands of the P=O (1240
1
1
1250 cm ) and C=O (1710 1740 cm ) (III, V, VI)
1
or C N groups (2320 cm ) (IV).
The steric structure of heterocycles III VI was
established by X-ray duffraction on an example of
2,3-(dimethoxycarbonyl)-1-(pentadiflurophenyl)-4,5,
EXPERIMENTAL
5
6,7-tetrafluorobenzo[d]- -phosphole 1-oxide (see
The IR spectra were measured on an IKS-29 spec-
figure and Tables 1, 2).
trometer in thin films (I, II) or KBr pellets (III VI).
F2
C3
F1
C2
F3
O1
C4
C1
P
F9
C12
C5
C7
F4
O3
C6
C11
F8
F5
C9
C15
C8
O5
C13
C10
C14
O2
C16
F6
F7
C17
C18
O4
5
Molecular structure of 2,3-(dimethoxycarbonyl)-1-(pentafluorophenyl)-4,5,6,7-tetrafluorobenzo[d]- -phosphole 1-oxide (VI).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 2 2004

SYNTHESIS OF SUBSTITUTED 4,5,8,7-TETRAFLUOROBENZO[d]- 5-PHOSPHOLES
191
Table 1. Interatomic distances in 2,3-(dimethoxycarbonyl)- Table 2. Bond angles in 2,3-(dimethoxycarbonyl)-1-
5
5
1-(pentafluorophenyl)-4,5,6,7-tetrafluorobenzo[d]-
phosphole 1-oxide (VI)
-
(pentafluorophenyl)-4,5,6,7-tetrafluorobenzo[d]-
phosphole 1-oxide (VI)
-
Bond
d,
Bond
d,
Angle
, deg
Angle
, deg
P O1
1.461(3)
1.811(3)
1.813(3)
1.818(3)
1.336(4)
1.337(4)
1.337(4)
1.343(4)
1.348(4)
1.332(4)
1.334(4)
1.346(4)
1.329(4)
1.189(4)
1.321(4)
1.457(4)
1.196(4)
1.316(4)
O5 C17
C1 C2
1.451(5)
1.366(5)
1.407(4)
1.386(5)
1.366(5)
1.382(5)
1.371(5)
1.474(5)
1.372(5)
1.379(5)
1.399(5)
1.375(5)
1.360(6)
1.377(5)
1.338(5)
1.512(5)
1.480(5)
O1PC1
116.37(16)
118.85(16)
91.02(16)
114.93(15)
108.77(15)
103.95(15)
116.7(3)
117.1(3)
119.6(3)
130.7(3)
109.7(2)
121.1(3)
118.2(3)
120.7(3)
119.9(3)
120.4(3)
119.7(3)
120.4(3)
119.5(3)
120.2(3)
121.2(3)
118.1(3)
120.7(3)
119.1(3)
127.8(3)
113.1(3)
116.0(3)
123.4(2)
C12C7P
120.5(3)
120.0(3)
116.5(3)
123.4(3)
120.2(3)
120.8(3)
118.9(3)
120.5(3)
119.8(4)
119.7(3)
119.7(3)
119.5(4)
120.8(3)
117.7(3)
121.0(3)
121.3(4)
114.7(3)
124.5(3)
120.8(3)
126.9(3)
123.2(3)
109.8(3)
124.9(3)
111.5(2)
123.6(2)
125.3(3)
124.5(3)
110.2(3)
P C1
O1PC15
C1PC15
C1PC7
F5C8C7
P C15
P C7
C1 C6
F5C8C9
C2 C3
C7C8C9
F1 C2
F2 C3
F3 C4
F4 C5
F5 C8
F6 C9
F7 C10
F8 C11
F9 C12
O2 C14
O3 C14
O3 C18
O4 C16
O5 C16
C3 C4
C7PC13
C15PC7
C14O3C18
C16O5C17
C2C1C6
C2C1P
F6C9C10
F6C9C8
C4 C5
C5 C6
C10C9C8
F7C10C11
F7C10C9
C11C10C9
F8C11C10
F8C11C12
C10C11C12
F9C12C11
F9C12C7
C11C12C7
C15C13C6
C15C13C14
C6C13C14
O2C14O3
O2C14C13
O3C14C13
C13C15C16
C13C15P
C16C15P
O4C16O5
O4C16C15
O5C16C15
C6 C13
C7 C8
C8 C9
C7 C12
C9 C10
C10 C11
C11 C12
C13 C15
C13 C14
C15 C16
C6C1P
F1C2C1
F1C2C3
C1C2C3
F2C3C4
F2C3C2
C4C3C2
F3C4C3
F3C4C5
C3C4C5
F4C5C6
F4C5C4
C6C5C4
C5C6C1
C5C6C13
C1C6C13
C8C7C12
C8C7P
1
The H NMR spectra were recorded on a Bruker AM-
500 NMR spectrometer (500 MHz) in the 2H stabiliza-
tion mode. The 31P NMR spectra were obtained on a
Bruker AC-200 spectrometer (81.4 MHz) in CDCl3
against 85% phosphoric acid.
X-ray diffraction analysis of crystals of 2,3-(di-
methoxycarbonyl)-1-(pentafluorophenyl)-4,5,6,7-tetra-
fluorobenzo[d]- -phosphole 1-oxide (IV) was carried
5
out on a CAD-4 diffractometer (MoK radiation, /2
scanning). Monoclinic crystals, C18H6F9O5P;
14.661(3), b 8.610(2), c 14.711(3) 97.49(3) , V
1841.1(7), space group 2(1)/n, 4, dcalc
a
pyridine was added. After that the reaction mixture
was stirred for 1 h. The precipitate was filtered off and
washed with 200 ml of ether. The solvent was re-
moved by distillation, and the residue was distilled in
a vacuum. Yield 23.9 g (52%), bp 57 80 C (0.5 mm),
,
P
Z
1.819 g/cm3. The structure was solved by the direct
method, R 0.0316 and RW 0.0991 [1911 reflections
with I > 2 (I)]. The general view of the molecule is
presented in the figure. The interatomic distances and
bond angles are listed in Tables 1, 2. The atomic co-
ordinates and equivalent isotropic temperature param-
eters are deposited in the Cambridge Structural
Database (CCDC registration number 178380).
1
n2D5 1.4490. IR spectrum, , cm : 1640 (C6F5), 1025
1
(P O C). H NMR spectrum (CDCl3), , ppm: 1.25 t
(6H, CH3), 4.00 m (4H, OCH2). 31P NMR spectrum:
150.6 ppm. Found, %: C 41.39, H 3.37, P 10.96.
P
C10H10F5O2P. Calculated, %: C 41.68, H 3.50,
P 10.75.
Diethyl (pentafluorophenyl)phosphonite (I). To
a solution of (pentafluorophenyl)magnesium chloride,
prepared from 35.0 g of pentafluorochlorobenzene and
8.5 g of magnesium in 200 ml of ether according to
the procedure [6], a solution of 25.0 g of diethyl
phosphorochloridite in 25 ml of anhydrous ether was
added dropwise with stirring at 60 C. The reaction
mixture was allowed to warm to 20 C, and 24.7 g of
Ethyl bis(pentafluorophenyl)phosphinite (II)
was prepared in a similar way from ethyl phosphoro-
dichloridite (11.7 g). Yield 18.9 g (58%), bp 88 90 C
(0.5 mm), n1D6 1.4812. IR spectrum, , cm : 1645
1
1
(C6F5), 1035 (P O C). H NMR spectrum (CDCl3),
, ppm: 1.27 t (3H, CH3), 4.02 m (2H, OCH2). 31P
NMR spectrum:
86.3 ppm. Found, %: C 41.19, H
P
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 2 2004

192
TRISHIN et al.
1.58, P 7.86. C14H5F10OP. Calculated, %: C 41.00,
H 1.23, P 7.55.
Found, %: C 54.22, H 3.48, N 7.67, P 6.90. C18H13
F4O4P. Calculated, %: C 54.01, H 3.27, P 7.74.
2,3-Disubstituted 1-ethoxy-4,5,6,7-tetrafluoro-
benzo[d]- -phosphole 1-oxides III V. To a boiling
2,3-(Dimethoxycarbonyl)-1-(pentafluorophenyl)-
4,5,6,7-tetrafluorobenzo[d]- 5-phosphole 1-oxide
(VI). To a boiling solution of 0.005 mol of ethyl bis-
(pentafluorophenyl)phosphinite (II) in 15 ml of an-
hydrous benzene, a solution of 0.005 mol of dimethyl
acetylenedicarboxylate in 10 ml of benzene was added
dropwise over the course of 30 min under argon. The
reaction mixture was refluxed for 3 h. Then the solvent
was removed at reduced pressure to leave a viscous
5
solution of 0.005 mol of diethyl (pentafluorophenyl)-
phosphonite (I) in 15 ml of anhydrous benzene (with
dimethyl acetylenedicarboxylate) or toluene (with the
other activated alkynes), a solution of alkyne in 10 ml
of corresponding solvent was added dropwise with
stirring under argon over the course of 20 30 min.
The reaction mixture was refluxed for 3 h, after which
the solvent was removed at reduced pressure. The
residue, a viscous oil of a light to dark brown color,
gradually crystallized on handling. According to the
brown oil. According to the 31P NMR spectrum, it
1
was fluorophosphorane VIb (
53.8 ppm, JPF
P
795.4 Hz). The product was dissolved in 20 ml of
THF containing 5 mmol of water and allowed to stand
for 12 h at 20 C. The solvent was removed at reduced
pressure, and the residue was triturated with 5 ml of a
2:1 ether hexane mixture. The resulting crystals were
filtered off and crystallized from a 1:2 benzene
hexane mixture. Yield 52%, mp 177 178 C. IR spec-
31P NMR spectrum, it was fluorophosphorane IIIb
Vb [ , ppm: 49.4 (IIIb), 50.4 (IVb), and 49.4
P
1
(Vb; JPF, Hz: 819.4 (IIIb), 832.7 (IVb), and 827.8
(Vb)]. The product was dissolved in 10 ml of an-
hydrous diethyl ether, and the solution was decanted
from an insignificant amount of undissolved oily
residue. Absolute ethanol, 2 ml, was added to the
solution, and the resulting mixture was kept for 0.5 h
at 20 C. The solvent was removed at reduced pressure,
the residue was dissolved in 10 ml of moist ether, and
the solution was allowed to stand in air to let the
solvent to evaporate. The residue was crystallized
from ether.
1
1
trum, , cm : 1710 (CO), 1245 (P=O). H NMR
spectrum (CDCl3), , ppm: 3.84 s [3H, CH3C(O)O],
4.02 s [3H, CH3C(O)O]. 31P NMR spectrum (CHCl3):
16.0 ppm. Found, %: C 42.69, H 1.08, P 6.25.
P
C18H6F9O5P. Calculated, %: C 42.88, H 1.20, P 6.14.
ACKNOWLEDGMENTS
2,3-(Dimethoxycarbonyl)-1-ethoxy-4,5,6,7-tetra-
5
The work was financially supported by the Mi-
nistry of Education of the Russian Federation (project
no. E 05-314) and the Russian Foundation for Basic
Research (project no. 03-03-32905).
fluorobenzo[d]- -phosphole 1-oxide (III). Yield
1
48%, mp 104 105 C. IR spectrum, , cm : 1710
1
(CO), 1250 (P=O), 1020 (POC). H NMR spectrum
(CDCl3), , ppm: 1.42 t (3H, CH3CH2), 4.45 m (2H,
CH2O), 3.89 s [3H, CH3C(O)O], 4.00 s [3H, CH3
REFERENCES
C(O)O]. 31P NMR spectrum (CHCl3):
30.7 ppm.
Found, %: C 44.23, H 3.07, P 8.32, CP14H11F4O6P.
Calculated, %: C 44.00; H 2.90; P 8.10.
1. Trishin, Yu.G., Chistokletov, V.N., and Petrov, A.A.,
Sov. Sci. Rev., Sect. B: Chem. Rev., 1991, vol. 51, no. 5,
pp. 1 59.
3-Cyano-1-ethoxy-2-phenyl-4,5,6,7-tetrafluoro-
5
benzo[d]- -phosphole 1-oxide (IV). Yield 70%, mp
2. Namestnikov, V.I., Tamm, L.A., Trishin, Yu.G., Bel’-
skii, V.K., and Chistokletov, V.N., Zh. Obshch. Khim.,
1998, vol. 68, no. 4, pp. 1398 1399.
1
121 122 C. IR spectrum, , cm : 2320 (CN), 1240
1
(P=O), 1015 (POC). H NMR spectrum (CDCl3), ,
ppm: 1.32 t (3H, CH3CH2), 4.32 m (2H, CH2O),
7.52 8.10 m (5H, Ph). 31P NMR spectrum (CHCl3):
3. Namestnikov, V.I., Trishin, Yu.G., and Bel’skii, V.K.,
Zh. Obshch. Khim., 1998, vol. 68, no. 8, pp. 1398 1399.
32.4 ppm. Found, %: C 55.64, H 2.82, P 8.62.
P
C17H10F4NO2P. Calculated, %: C 55.60, H 2.74,
P 8.43.
4. Trishin, Yu.G., Namestnikov, V.I., and Bel’skii, V.K.,
Zh. Obshch. Khim., 1999, vol. 69, no. 10, pp. 1749
1750.
1-Ethoxy-3-methoxycarbonyl-2-phenyl-4,5,6,7-
tetrafluorobenzo[d]- 5-phosphole 1-oxide (V).
5. Trishin, Yu.G., Namestnikov, V.I., and Bel’skii, V.K.,
1
Zh. Obshch. Khim., 2001, vol. 71, no. 3, pp. 500 512.
Yield 75%, mp 118 119 C. IR spectrum, , cm :
1
1740 (CO), 1240 (P=O), 1010 (POC). H NMR spec-
6. Sintezy ftororganicheskikh soedinenii (Syntheses of
Organofluorine Compounds), Knunyants, I.L. and
Yakobson, G.G., Eds., Moscow: Khimiya, 1973, 1st ed.,
p. 140.
trum (CDCl3, , ppm: 1.29 t (3H, CH3CH2), 4.26 m
(2H, CH2O), 3.85 s [3H, CH3C(O)O], 7.40 7.69 m
(5H, Ph). 31P NMR spectrum (CHCl3):
35.9 ppm.
P
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 2 2004