C-phosphorylation of N-arylpyrroles

Article abstract of DOI:10.1002/hc.10012

Phosphorylation of N-arylpyrroles with phosphorus tribromide proceeds regioselectively at the position 2 of the heterocyclic system. A 2-to-3 migration of the dibromophosphino group has been discovered, with its ease depending on the electronic nature of a substituent on the phenyl ring, solvent polarity, and the presence of pyridine hydrobromide in the reaction mixture. Further phosphorylation of 2- and 3-monophosphorylated N-arylpyrroles regioselectively involves the respective positions 4 and 5 of the heterocycle and is governed by the electron-acceptor effect of the phosphorus-containing substituent.

Full text of DOI:10.1002/hc.10012

Heteroatom Chemistry
Volume 13, Number 3, 2002
C-Phosphorylation of N-Arylpyrroles
Sergey P. Ivonin,1 Andrew A. Tolmachev,2 and Alexander M. Pinchuk2
1Dnepropetrovsk State University, Dnepropetrovsk-10, 320625 Ukraine
2Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Kiev-94,
253660 Ukraine
Received 19 June 2001; revised 1 September 2001
action products impelled us to the study of ef-
ABSTRACT: Phosphorylation of N-arylpyrroles with
fects caused by various factors on the phosphoryla-
phosphorus tribromide proceeds regioselectively at the
tion regioselectivity and the rate for N-arylpyrroles.
position 2 of the heterocyclic system. A 2-to-3 migra-
An interesting challenge was also to ascertain the
tion of the dibromophosphino group has been disco-
possibility for the dibromophosphino group in 2-
vered, with its ease depending on the electronic nature
(N-arylpyrrolyl)dibromophosphines to undergo a
of a substituent on the phenyl ring, solvent polarity,
migration.
and the presence of pyridine hydrobromide in the
reaction mixture. Further phosphorylation of 2-
and 3-monophosphorylated N-arylpyrroles regioselec-
RESULTS AND DISCUSSION
tively involves the respective positions 4 and 5 of
the heterocycle and is governed by the electron-
acceptor effect of the phosphorus-containing sub-
The phosphorylation of N-arylpyrroles 1–4 with
phosphorus tribromide, carried out in the pres-
ence of pyridine in methylene chloride at 20 C,
was found to proceed regioselectively (in contrast
to the results when benzene was used as a sol-
vent) to generate N-aryldibromophosphinopyrro-
les 6–9 (Scheme 1). N-(p-Nitrophenyl)pyrrole (5)
could only be phosphorylated in pyridine medium
to furnish the N-aryldibromophosphinopyrrole (10).
Unlike 2-(1-methylpyrrolyl)dibromophosphine, the
N-aryldibromophosphinopyrroles 6–9 have been
isolated in an analytically pure state, as crystalline
substances stable in the absence of atmospheric
moisture.
Resonances of N-aryldibromophosphinopyr-
roles 6–9 in the 31P NMR spectra are observable
in the range = 122–126 ppm (Table 1), which
suggests that the reactions involve the position 2 of
the pyrrole ring, as was proved by us previously [2].
The N-aryldibromophosphinopyrroles 6–9 were
converted into thioamides 11–15 in high yields
(Scheme 1). For thioamide 12, an informative
structure-supporting 13C NMR (Table 2) signal arises
from the C2 atom (␦ = 112.1 ppm, JCP = 150.5 Hz).
C
stituent. 2002 Wiley Periodicals, Inc. Heteroatom Chem
13:223–228, 2002; Published online in Wiley Interscience
(www.interscience.wiley.com). DOI 10.1002/hc.10012
INTRODUCTION
Previously, we showed that phosphorylation of N-
methylpyrrole with phosphorus tribromide in ben-
zene in the presence of triethylamine takes place
regioselectively at position 2 of the heterocyclic
system. Interestingly, the resulting 2-dibromophos-
phino substituent can isomerize to the 3-position
in polar solvents [1]. By contrast, N-phenylpyrrole
is phosphorylated with phosphorus tribromide in
benzene nonregioselectively to provide a 1:1 mixture
of 2- and 3-N-phenyldibromophosphinopyrroles.
The dissimilarity in the stereoselectivity of the re-
Correspondence to: Sergey P. Ivonin; e-mail: ivonin@dp.ukrtel.
net.
c
2002 Wiley Periodicals, Inc.
223

224 Ivonin, Tolmachev, and Pinchuk
more than 5% of 3-substituted isomers can be found
in them, as determined by 31P NMR spectroscopy.
As 2-(N-methylpyrrolyl)dibromophosphine was not
isolated in an analytically pure state, it might be
supposed that it isomerised because of the presence
of the pyridine hydrobromide impurity [1]. It was
our intention to verify this suggestion for the N-
aryldibromophosphinopyrroles 6–9.
It turned out that, on addition of 1 equiv of
pyridine hydrobromide to solutions of the N-aryldi-
bromophosphinopyrroles 6–9 in methylene chloride,
6 and 7 underwent isomerization into 16 and 17
(Scheme 2), whereas 8 and 9 did not. A similar situa-
tion occurred on aging of the reaction mixtures that
resulted from phosphorylation of arylpyrroles 1–4
with phosphorus tribromide in methylene chloride.
31P NMR resonances of dibromophosphines 16
and 17 were observed in the range = 141–143
ppm suggesting that the dibromophosphino group
had migrated to the position 3 of the pyrrole ring.
N-aryldibromophosphinopyrroles 16 and 17 fur-
nished thioamides 18 and 19 in high yields
(Scheme 2). The signal from C3 in the 13C NMR
(Table 2) spectrum of compound 19 (␦ = 120.7 ppm,
JCP = 73.2 Hz) is indicative of its structure.
SCHEME 1
Phosphorylation selectivity was significantly
influenced by the basicity of the medium and the
method of phosphorus tribromide delivery into the
reaction mixture. Use of the more basic triethyl-
amine instead of pyridine or addition of undiluted
phosphorus tribromide to the reaction mixture re-
sults in the formation of a 5–10% yield of the 3-
substituted isomer. A material effect on the reaction
rate is caused by the nature of a substituent at the
para position of the phenyl ring. Thus, the reaction
time markedly lengthens with increasing electron ac-
ceptor ability of the substituent R in the compound
series 1–5 (see Table 3).
Unlike 2-(N-methylpyrrolyl)dibromophosphine
that completely isomerizes in methylene chloride
at 20 C in 2h, solutions of the N-aryldibromophos-
phinopyrroles 6–9 are stable under analogous condi-
tions. Thus, on holding the solutions for 1 month, no
The above-presented data provided evidence that
a significant effect on the isomerization rate was
caused by the nature of a substituent at the nitro-
gen atom. For instance, the time of isomerization
increases notably in going both from the N-methyl to
TABLE 1 Yields, Data of Elemental Analysis, and 31P NMR Spectroscopic Characteristics for Compounds 6–27
Found % (Calcd %)
No Yield (%)
MP ( C)
Formula
(CH Cl )
P
N
P
2
2
6
7
8
69
88
84
57
90
91
87
95
74
64
68
86
93
72
64
73
81
93
86
88
93
oil
oil
87
176
83
157
131
207
247
76
C12H12Br2NOP
126.5
126.0
125.9
123.9
61.0a
61.0a
60.7a
62.3a
60.3a
143.4
141.8
69.4a
68.2a
59.4; 138.7
59.3; 137.1
59.8; 137.2
59.5; 136.8
59.1; 68.2a
59.3; 67.8a
59.5; 67.9a
60.0; 67.3a
8.15 (8.22)
8.77 (8.93)
9.35 (9.30)
7.44 (7.52)
7.59 (7.35)
7.98 (7.91)
8.35 (8.21)
6.72 (6.79)
7.17 (7.33)
8.14 (8.22)
9.12 (8.93)
7.28 (7.35)
7.67 (7.91)
10.07 (10.13)
10.81 (10.66)
10.83 (10.92)
9.38 (9.59)
9.51 (9.45)
9.77 (9.90)
10.27 (10.13)
8.71 (8.97)
3.58 (3.72)
3.95 (4.04)
4.17 (4.21)
C
C
11H10Br2NP
10H8Br2NP
9
C10H7Br3NP
3.21 (3.40)
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
20H28N3O3PS
19H26N3O2PS
18H24N3O2PS
18H23BrN3O2PS
18H23N4O4PS
12H12Br2NOP
11H10Br2NP
20H28N3O3PS
19H26N3O2PS
20H27Br2N3O3P2S
19H25Br2N3O2P2S
18H23Br2N3O2P2S
18H22Br3N3O2P2S
28H43N5O5P2S2
27H41N5O4P2S2
26H39N5O4P2S2
26H38BrN5O4P2S2
10.02 (9.97)
10.81 (10.73)
11.35 (11.13)
9.29 (9.21)
13.34 (13.26)
3.57 (3.72)
oil
3.95 (4.04)
105
157
127
137
135
198
112
145
157
243
10.16 (9.97)
10.81 (10.73)
7.98 (6.87)
7.31 (7.23)
7.53 (7.41)
6.64 (6.50)
10.92 (10.68)
11.44 (11.19)
11.37 (11.45)
10.32 (10.14)
aSolvent: C6H6.

C-Phosphorylation of N-Arylpyrroles 225
TABLE 2 13C NMR Data for Compounds 12, 19 in CDCl3: , Multiplicity, J (Hz)
Het (JCP
)
Ar
No
C2
C3
C4
C5
C1
C2, C6 C3, C5
C4
Others
12 112.1 d
(150.5)
19 137.3 d
108.9 d
(11.9)
110.0 d
(12.5)
130.6 d
(7.8)
123.5 d
(12.8)
122.2 t
140.1 s 130.8 s 126.3 s 137.0 s 20.5 s (CH3 Ar); 45.1 s (O CH2);
66.0 d (J = 7.5, N CH2)
(13.9)
120.7 t
(73.2)
146.2 s 127.5 s 125.3 s 145.3 s 20.5 s (CH3 Ar); 45.1 s (O CH2);
66.0 d (J = 6.3, N CH2)
(45.1)
the N-aryl substituted pyrrole and from the p-ethoxy
(16) to the p-methyl (17) substituted N-arylpyrrole
(Table 4). For the N-aryldibromophosphinopyrroles
8 and 9, the migration of the dibromophosphino
group is so slow that it is of no synthetic value. To
be specific, 31P NMR spectroscopic data suggest that
the reaction has taken place to the extent of less than
5% during 2 months. The rate of isomerization
was also substantially influenced by basicity of the
medium. To exemplify, the migration of the dibromo-
phosphino group is considerably slowed down by
the presence of an excess of pyridine in the reaction
mixture (see Table 4).
SCHEME 2
The evidence presented in Table 4 leads us to in-
fer that the rearrangement in question is initiated by
pyridine hydrobromide and its mechanism may be
that shown in Scheme 3.
an electron-acceptor substituent on phosphorus (a
thioamide group) in compounds 11–14 and 18, 19
notably reduces the reactivity of the heterocyclic
system to phosphorus tribromide and the reaction
can take place only provided pyridine is used
both as a solvent and a base. The phosphorylation
proceeds regioselectively according to the electron-
acceptor effect of the first-introduced substituent.
For instance, the substituent residing at the po-
sition 2 of the heterocycle (as in amides 11–14)
orients phosphorylation to the position 4 to furnish,
in high yields, N-aryldibromophosphinopyrroles
20–23 which, in turn, afford thioamides 24–27. A
thioamide substituent at the position 3 of the hetero-
cyclic ring (as in amides 18 and 19) causes phospho-
rylation at the position 5 and that results in forma-
tion of 28 and29, identified by their 31P NMR spectra
and characterized by conversion into thioamides 24
and 25 (Scheme 4). The 31P NMR spectra of 20–23 in-
clude a singlet peak at = 140 ppm, evidently arising
from the dibromophosphino group at the position 4
At the first stage of phosphorylation, the kineti-
cally controlled product A is formed, and the equi-
librium of A with pyrrole and phosphorus tribro-
mide is established in the reaction mixture because
of the HBr-induced lability of the C P bond. The
rate of formation of product B is much less than
that of A, but the former is more stable thermody-
namically and hence accumulates in the reaction
mixture. In support of the assumed mechanism,
solutions of isomeric N-aryldibromophosphinopyr-
roles 7 and 17 in methylene chloride were satu-
rated with dry hydrogen bromide at 20 C. The 31P
NMR spectrum showed that the peak arising from 7
(␦P = 126.0 ppm) vanished, as that from phosphorus
tribromide (␦P = 228.3 ppm) appeared and increased.
Contrastingly, N-aryldibromophosphinopyrrole (17)
was stable under these conditions.
As with N-methylpyrroles, it is possible to
successively introduce two phosphorus-containing
substituents in an N-arylpyrrole molecule. However,
TABLE 4 Relation of Isomerization by Basicity of the Medium
Product
TABLE 3 Time of Reaction for Compounds 6–10
16
17
Product
Reaction time (h)
6
0.5
7
2
8
8
9
24
10a
170
Pyridine: PBr3 ratio
Isomerization
1:1
1
3:1
3
1:1
2
3:1
8
time (weeks)
aIn pyridine.

226 Ivonin, Tolmachev, and Pinchuk
TABLE 5 Time of Phosphorylation for Compounds 20–23,
28, and 29
Product
Reaction time (weeks)
20
2
21
6
22
8
23
20
28
2
29
5
General Procedure for Preparation
of N-Arylpyrrolyldibromophosphines 6–9
SCHEME 3
To a stirred solution of each pyrrole 1–4 (0.01 mol)
and pyridine (0.01 mol) in methylene chloride
(20 ml) was added dropwise a solution of phosphorus
tribromide (0.01 mol) in methylene chloride (20 ml)
over 10 min. The reaction mixture was allowed to
stand at room temperature (see Table 3). After filtra-
tion of the mixture, the filtrate was evaporated under
reduced pressure. The product was crystallized from
octane.
of the pyrrole ring. As regards the reaction mixtures
containing dibromophosphines 28 and 29, an ana-
logous singlet is observed at = 115 ppm, suggesting
that phosphorylation has involved the position 5.
The phosphorylation rate is essentially governed
by the nature of a substituent at the para position
of the phenyl ring. Thus, the reaction is materially
slowed down with increasing electron acceptor abil-
ity of the substituent R in the compounds series
11–14 and in going from 18 to 19 (see Table 5).
An attempt to selectively phosphorylate arylpyr-
role 2 with 2 equivalants of phosphorus tribromide
failed: The 31P NMR spectrum of the reaction mix-
ture exhibits four signals that can be assigned to
isomeric bisdibromophosphines 30–32 contained in
the 1:1:0.5 ratio (Scheme 5). These products could
not be isolated in an analytically pure state.
General Procedure for Preparation
of Thioamides 11–14
To a stirred solution of each compound 6–9
(0.01 mol) in benzene (50 ml) was added dropwise
a solution of morpholine (0.02 mol) and triethylam-
mine (0.03 mol) in benzene (50 ml) over 10 min; 4 h
later sulfur (0.01 mol) was added to the reaction mix-
ture. After heating at 60 C for 2 h, the mixture was fil-
tered and the filtrate was evaporated under reduced
pressure. The product was crystallized from octane.
EXPERIMENTAL
31P, 1 H, and 13C NMR spectra were run on a Varian–
VXR 300 spectrometer with TMS being used as
an internal standard for 1H and 13C signals, and
85% H3PO4 as an external standard for 31P signals
(Tables 1, 2, and 6). All manipulations were carried
out in anhydrous solvents.
2-(1-(p-Nitrophenyl))pyrrolyldimorpholinothio-
phosphonate (15)
To a solution of pyrrole 5 (0.001 mol) in pyri-
dine (10 ml) was added a solution of phosphorus
tribromide (0.001 mol) in pyridine (10 ml). After
1 week (␦P = 122.4 ppm), a solution of morpholine
(0.002 mol) and triethylamine (0.003 mol) in benzene
(20 ml), followed (0.5 h later) by sulfur (0.001 mol),
was added to the reaction mixture. After heating the
mixture at 70 C for 2 h, it was allowed to cool and
then filtered. The filtrate was evaporated, and the
residue was dissolved in methylene chloride (50 ml)
and washed with water (2 30 ml). After drying the
SCHEME 4
SCHEME 5

C-Phosphorylation of N-Arylpyrroles 227
TABLE 6 1H NMR Data for Compounds 6–27 in CDCl3: , Multiplicity, J (Hz)
No
3-H (2-H)
4-H
5-H
Others
6
6, 62 dd (JHP = 3.2) 6.21 t (JHP = JHH
(JHH = 2.5) = 2.5)
7.31 dd (JHP = 4.1)
(JHH = 2.5)
1.36 t JHH = 9.0 (3H, Me); 4.10 k
JHH = 9.0 (2H, O CH2 Me);
6.77 d JHH = 8.4 (2H, m-Ar);
7.24 d JHH = 8.4 (2H, o-Ar)
7
6, 67 dd (JHP = 4.3) 6.21 t (JHP = JHH
7.31 dd (JHP = 4.3)
(JHH = 2.5)
1.98 s (Me); 6.78 d JHH = 8.1
(JHH = 2.5)
6.58 m
= 2.7)
(2H, m-Ar); 6.97 dd JHH = 8.1;
JHP = 2.5 (2H, o-Ar)
8
9
6.18 t (JHP = JHH
= 3.6)
7.32 dd (JHP = 1.5)
(JHH = 3.6)
6.91 m (3H, m-Ph + p-Ph); 7.01 m
(2H, o-Ph)
6, 35 dd (JHP = 6.3) 7.06 t (JHP = JHH
7.58 dd (JHP = 6.0)
(JHH = 3.0)
7.73 d JHH = 8.1 (2H, m-Ar); 7.85 d
JHH = 8.1 (2H, o-Ar)
(JHH = 3.0)
= 3.0)
11
6, 79 dd (JHP = 5.7) 6, 30 dd (JHP = 4.2) 7.17 m
1.34 t JHH = 9.3 (3H, Me); 3.0 m
(8H, CH2 N); 3.50 m (8H, CH2 O);
4.08 k JHH = 9.3 (2H, O CH2 Me); 6.97 d
JHH = 8.7 (2H, m-Ar);
(JHH = 2.7)
(JHH = 2.7)
7.54 d JHH = 8.7 (2H, o-Ar)
12
6, 81 dd (JHP = 2.9) 6.30 t (JHP = JHH
(JHH = 2.5) = 2.5)
6, 99 dd (JHP = 5.6) 2.45 s (3H, Me); 3.1 m (8H, CH2 N); 3.50 m
(JHH = 2.5)
(8H, CH2 O); 7.21 d JHH = 8.1 (2H, m-Ar);
7.50 d JHH = 8.1 (2H, o-Ar)
13
14
6.82 m
6, 32 dd (JHP = 3.6) 7.03 m
(JHH = 2.7)
3.1 m (8H, CH2 N); 3.50 m (8H, CH2 O);
7.41 m (3H, m-Ph + p-Ph); 7.64 m (2H, o-Ph)
3.0 m (8H, CH2 N); 3.40 m (8H, CH2 O);
7.59 d JHH = 8.1 (2H, m-Ar);
6.84 m
6.85 m
7.06 m
6, 36 dd (JHP = 6.0) 7.26 m
(JHH = 3.0)
7.66 d JHH = 8.1 (2H, o-Ar)
15
16
6, 50 dd (JHP = 5.1) 7.20 m
(JHH = 3.0)
3.20 m (8H, CH2 N); 3.70 m (8H, CH2 O);
7.52 d JHH = 9.0 (2H, m-Ar);
8.32 d JHH = 9.0 (2H, o-Ar)
6.30 t (JHP = JHH
= 3.3)
6.42 t (JHP = JHH
1.44 t JHH = 9.0 (3H, Me);
= 3.3)
4.07 k JHH = 9.0 (2H, O CH2 Me); 6.95 d,
JHH = 8.4 (2H, m-Ar); 7.33 d,
JHH = 8.4 (2H, o-Ar)
17
18
7.48 t (JHP = JHH
= 2.5)
6.82 t (JHP = JHH
= 2.5)
7.19 t (JHP = JHH
= 2.5)
2.41 s (Me); 7.26 s (4H, Ar)
7.18 m
6, 31 dd (JHP = 2.1) 6.79 m
(JHH = 3.0)
1.34 t JHH = 9.6 (3H, Me); 3.0 m
(8H, CH2 N); 3.50 m (8H, CH2 O);
4.05 k JHH = 9.6 (2H, O CH2 Me); 6.97 d,
JHH = 9.0 (2H, m-Ar); 7.55 d,
JHH = 9.0 (2H, o-Ar)
19
20
7.19 t (JHP = JHH
= 2.5)
6, 32 dd (JHP = 6.4) 6.81 t (JHP = JHH
2.36 s (3H, Me); 3.0 m
(JHH = 2.5)
= 2.5)
(8H, CH2 N); 3.40 m (8H, CH2 O); 7.25 d,
JHH = 8.1 (2H, m-Ar); 7.54 d,
JHH = 8.1 (2H, o-Ar)
6.9 m
–
7.38 dd (JHP = 8.1)
JHH = 2.1
1.44 t JHH = 9.6 (3H, Me); 3.1 m
(8H, CH2 N); 3.6 m (8H, CH2 O);
4.08 k JHH = 9.6 (2H, O CH2 Me); 6.9 m
(3H, H3+ m-Ar); 7.47 d JHH = 8.4 (2H, o-Ar)
2.44 s (3H, Me); 3.4 m
21
6, 93 dd (JHP = 5.0)
(JHP = 2.1)
–
6, 32 d (JHP = 1.5)
(8H, CH2 N); 3.9 m (8H, CH2 O); 7.27 s
(4H, Ar)
22
23
6.9 m
–
–
6, 35 d (JHP = 1.5)
6, 39 d (JHP = 1.5)
3.2 m (8H, CH2 N); 3.6 m (8H, CH2 O);
7.4 m (3H, m-Ph + p-Ph); 7.6 m (2H, o-Ph)
3.2 m (8H, CH2 N); 3.6 m (8H, CH2 O);
7.59 d JHH = 8.4 (2H, m-Ar);
6, 98 dd (JHP = 4.0)
(JHP = 2.1)
7.66 d JHH = 8.4 (2H, o-Ar)
24
6.9 m
–
7.35 t (JHP = JHP
= 8.7)
1.43 t JHH = 10.0 (3H, Me); 3.0 m
(8H, CH2 N); 3.6 m (8H, CH2 O); 4.06 k
JHH = 10.0 (2H, O CH2 Me); 6.9 m
(3H, H3+ m-Ar); 7.49 d, JHH = 8.1 (2H, o-Ar)
(Continued)

228 Ivonin, Tolmachev, and Pinchuk
TABLE 6 Continued
No
3-H (2-H)
4-H
5-H
Others
2.37 s (3H, Me); 3.0 m
25
6.93 t (JHP = JHP
= 5.0)
–
7.44 d (JHP = 4.5)
(8H, CH2 N); 3.50 m (8H, CH2 O); 7.28 d
JHH = 7.2 (2H, m-Ar); 7.50 d
JHH = 7.2 (2H, o-Ar)
26
27
6, 98 dd (JHP = 6.1)
(JHP = 3.0)
–
–
7.55 d (JHP = 6.5)
7.59 d (JHP = 6.2)
3.1 m (8H, CH2 N); 3.5 m (8H, CH2 O);
7.5 m (3H, m-Ph + p-Ph); 7.9 m (2H, o-Ph)
3.2 m (8H, CH2 N); 3.6 m (8H, CH2 O);
7.69 d JHH = 8.1 (2H, m-Ar);
6, 96 dd (JHP = 4.0)
(JHP = 2.1)
7.92 d JHH = 8.1 (2H, o-Ar)
solution with sodium sulfate, it was evaporated and
the residue was washed with benzene on a filter.
of phosphorus tribromide (0.01 mol) in pyridine
(10 ml). The reaction mixture was allowed to stand at
room temperature (see Table 5). After filtration of the
mixture, the filtrate was evaporated under reduced
pressure. The product was purified by precipitation
from benzene with hexane.
General Procedure for Preparation
of N-Arylpyrrolyldibromophosphines 16 and 17
Method A. To a stirred solution of each pyr-
role 1 and 2 (0.01 mol) and pyridine (0.01 mol) in
methylene chloride (20 ml) was added dropwise a
solution of phosphorus tribromide (0.01 mol) in
methylene chloride (20 ml) over 10 min. The reac-
tion mixture was allowed to stand at room tempera-
ture (see Table 4). After filtration of the mixture, the
filtrate was evaporated under reduced pressure. The
product was crystallized from octane.
General Procedure for Preparation
of Each bis-Thioamide 24–27
To a stirred solution of each compound 20–23
(0.01 mol) in benzene (50 ml) was added dropwise a
solution of morpholine (0.02 mol) and triethylam-
mine (0.03 mol) in benzene (50 ml) over 10 min;
4 h later sulfur (0.01 mol) was added to the reaction
mixture. After heating at 60 C for 2 h, the mixture
was filtered and the filtrate was evaporated under re-
duced pressure. The product was crystallized from
ethanol.
Method B. To a stirred solution of each com-
pound 6 and 7 (0.01 mol) in methylene chlor-
ide (50 ml) was poured pyridine hydrobromide
(0.01 mol) and the mixture was allowed to stand at
room temperature (see Table 4). After filtration of the
mixture, the filtrate was evaporated under reduced
pressure. The product was crystallized from octane.
Preparation of bis-Thioamides 24, 25 from
Thioamides 18, 19. To a stirred solution of each
thioamide 18 and 19 (0.01 mol) in pyridine (50 ml)
was added dropwise a solution of phosphorus tri-
bromide (0.01 mol) in pyridine (10 ml). The reaction
mixture was allowed to stand at room temperature
(see Table 3), and then a solution of morpholine
(0.02 mol) and triethylamine (0.03 mol) in benzene
(20 ml), followed (2 h later) by sulfur (0.01 mol) was
added to it. After heating the mixture at 70 C for
4 h, it was allowed to cool and then filtered. The fil-
trate was evaporated under reduced pressure and the
product was crystallized from ethanol.
General Procedure for Preparation
of Thioamides 18 and 19
To a stirred solution of each compound 16 and 17
(0.01 mol) in benzene (50 ml) was added dropwise a
solution of morpholine (0.02 mol) and triethylam-
mine (0.03 mol) in benzene (50 ml) over 10 min;
4 h later sulfur (0.01 mol) was added to the reaction
mixture. After heating at 60 C for 2 h, the mixture
was filtered and the filtrate was evaporated under re-
duced pressure. The product was crystallized from
octane.
REFERENCES
General Procedure for Preparation
of N-Arylpyrrolyldibromophosphines 20–23
[1] Ivonin, S. P.; Terikovska, T. E.; Chaikovskaya, A. A.;
Marchenko, A. P.; Koydan, G. N.; Pinchuk, A. M.;
Tolmachev, A. A. Heteroat Chem 1999, 10, 213–221.
[2] Tolmachev, A. A.; Ivonin, S. P.; Pinchuk, A. M. Heteroat
Chem 1995, 6, 407–412.
To a stirred solution of thioamide 11–14 (0.01 mol)
in pyridine (50 ml) was added dropwise a solution