Synthesis and properties of (thieno[2,3-b]pyridin-3-yl) iminotriphenylphosphoranes. Molecular structure of (2-benzoyl-4-methoxymethyl-6- methylthieno[2,3-b]pyridin-3-yl)iminotriphenylphosphorane

Article abstract of DOI:10.1007/s10593-005-0104-9

Iminophosphoranes containing a thieno[2,3-b]pyridine fragment were obtained through a sequence of reactions: 1) alkylation of 3-cyano-2(1H)-pyridinethiones in alkaline medium by an α-halocarbonyl compound with subsequent Thorpe-Ziegler cyclization of the

Full text of DOI:10.1007/s10593-005-0104-9

Chemistry of Heterocyclic Compounds, Vol. 40, No. 12, 2004
SYNTHESIS AND PROPERTIES OF
(THIENO[2,3-b]PYRIDIN-3-YL)IMINOTRIPHENYL-
PHOSPHORANES. MOLECULAR STRUCTURE OF
(2-BENZOYL-4-METHOXYMETHYL-6-METHYL-
THIENO[2,3-b]PYRIDIN-3-YL)IMINO-
TRIPHENYLPHOSPHORANE
E. A. Kaigorodova, V. K. Vasilin, M. M. Lipunov, V. E. Zavodnik, and G. D. Krapivin
Iminophosphoranes containing a thieno[2,3-b]pyridine fragment were obtained through a sequence of
reactions: 1) alkylation of 3-cyano-2(1H)-pyridinethiones in alkaline medium by an α-halocarbonyl
compound with subsequent Thorpe–Ziegler cyclization of the resultant 2-thioalkylpyridines to give
3-aminothieno[2,3-b]pyridines, 2) diazotization of the amino group and nucleophilic substitution of the
diazonium group by an azido group without isolation of the diazonium salts, and 3) reaction of the
3-azidothieno[2,3-b]pyridines with triphenylphosphine.
Keywords: 3-aminothieno[2,3-b]pyridines, 3-azidothieno[2,3-b]pyridines, 3-cyano-2(1H)-pyridine-
thiones, (thieno[2,3-b]pyridin-3-yl)-iminotriphenylphosphoranes, molecular structure, synthesis.
Iminophosphoranes, in light of their electronic structure, are promising intermediates for the synthesis of
many compounds of different types [1-3]. In the present work, we synthesized thieno[2,3-b]-
pyridinyliminophosphoranes, for which no data have been available in the literature, and studied the
physicochemical properties of these compounds.
Pyridinethione 1, α-haloacetic acid derivatives 2a-d, and phenacyl bromide 2e served as the starting
compounds for the preparation of (thieno[2,3-b]pyridin-3-yl)iminotriphenylphosphoranes.
The reaction of pyridinethione 1 with α-halocarbonyl compounds 2a-e were carried out in the presence
of two equivalents of KOH to bind the hydrogen halide liberated and provide for the Thorpe–Ziegler
isomerization of intermediate S-alkyl derivatives 3a-e to give 3-aminothieno[2,3-b]pyridines 4a-e (Scheme 1).
3-Aminothieno[2,3-b]pyridines 4 are bright-yellow compounds, which are highly soluble in polar
solvents (Table 1). Pyridines 4a and 4e have already been prepared and some of their properties have been
reported in our previous work [4, 5].
The structure of the 3-aminothieno[2,3-b]pyridines was confirmed by IR, UV, and 1H NMR
spectroscopy (Table 2). The IR spectra of 4a-e lacked the nitrile group band at 2210 cm-1 and thioamide group
band at 1215 cm-1 characteristic for starting pyridinethione 1 but have stretching bands for the amino group N–H
bond at 3465-3400 and 3330-3255 cm-1 as well as stretching bands for the conjugated carbonyl group in ester 4a
__________________________________________________________________________________________
Kuban State Technological University, 350072 Krasnodar, Russia; e-mail: organics@kubstu.ru.
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1853-1862, December, 2004. Original
article submitted July 5, 2002; revision submitted May 10, 2004.
1600
0009-3122/04/4012-1600©2004 Springer Science+Business Media, Inc.

Scheme 1
O
O
O
X
O
R
NH2
CN
S
CN
2a–e
KOH
O
R
KOH
S
N
H
N
S
R
N
4a–e
O
1
3a–e
2-4 а R = OEt, b R = N(CH2Ph)2, c R = NPh2, d R = morpholino, e R = Ph;
а, е Х = Br, b-d Х = Cl
1
at 1660 cm-1, amides 4b-d at 1600-1590 cm-1, and ketone 4e at 1595 cm-1. The H NMR spectra of 4a-e have
signals for the protons of all the groups; the broad singlet of the amino group is found at 6.13-8.12 ppm.
TABLE 1. Physicochemical Properties of 3-Aminothieno[2,3-b]pyridines
4a-e, 3-Azidothieno[2,3-b]pyridines 6a-e, and (Thieno[2,3-b]pyridin-3-yl)-
iminotriphenylphosphoranes 7a-e
Found, %
Calculated, %
mp,
(or dec. p.)
°С
——————
Com-
pound
Empirical
formula
UV spectrum, λmax
nm (log ε)
,
Yield,
%
С
Н
N
78
4a
4b
4c
4d
4e
С13H16N2O3S
C25H25N3O2S
C23H21N3O2S
С15Н19N3O3S
C17H16N2O2S
55.68 5.76
55.70 5.75
9.95
9.99
147.5-148 208 (4.35), 240 (4.05),
288 (4.61), 373 (3.81)
69.53 5.84
69.58 5.84
9.70
9.74
128-129
187-188
157-158
137-138
207 (4.56), 243 (3.93),
293 (3.27), 367 (3.59)
69
90
71
92
68.64 5.24
68.46 5.25
10.39
10.41
207 (4.62), 298 (4.28),
393 (3.91)
56.02 5.94
56.06 5.96
13.05
13.07
207 (4.33), 242 (3.95),
290 (4.27), 366 (3.61)
65.31 5.13
65.36 5.16
8.93
8.97
212 (4.44), 283 (4.23),
311 (4.40), 415 (4.05)
6a
6b
6c
6d
6e
7a
C13H14N4O3S
C25H23N5O2S
C23H19N5O2S
C15H17N5O3S
C17H14N4O2S
50.97 4.61
50.93 4.58
65.63 5.07
65.59 5.00
64.32 4.46
64.27 4.43
51.86 4.93
51.85 4.91
18.29 (118-119)
18.22
—
82
82
97
50
74
69
15.31
15.27
56-58
—
16.31 (177-178)
16.30
20.16 (138-139)
20.14
—
60.28 4.17
60.34 4.20
16.49
16.56
115-117
C31H29N2O3PS 68.82 5.38
68.87 5.41
5.14
5.18
235-236
208 (4.83), 246 (4.32),
286 (4.37), 388 (3.99)
7b
7с
7d
7e
С43H38N3O2S
74.66 5.50
74.65 5.54
6.03
6.07
214-215
289-290
238-239
215-216
209 (4.97), 217 (4.42),
340 (3.76)
47
72
64
56
C41H34N3O2РS 74.16 5.15
6.29
6.33
206 (4.80), 250 (4.77),
394 (3.83)
74.19 5.16
C33H32N3O3РS 68.13 5.52
7.19
7.22
208 (4.89), 263 (4.39),
340 (3.82)
68.14 5.54
C35H29N2O2PS 73.38 5.10
73.41 5.10
4.86
4.89
208 (4.85), 280 (4.23),
322 (4.15), 442 (3.86)
1601

TABLE 2. Spectral Data of Products
IR spectrum, ν, cm-1
1H NMR spectrum, δ, ppm (J, Hz)
НPy
(1H, s)
Com-
pound
СН3
(3H, s)
NH2
О−СН3
(3H, s)
О−СН2
(2H, s)
С=О
C−O−C
other signals
9
(N3)
1
2
3
4
5
6
7
8
4a
1660
3420,
3330
1275*,
1190*,
1120
2.56
3.41
4.82
7.20
1.32 (3Н, t , J = 7.2, СН2CH3); 4.30 (2Н, q, J = 7.2, CH2CH3);
6.92 (2Н, br. s, NH2)
4b
1595
3400,
3305
1145,
1100,
1070
2.80
3.43
4.81
7.08
4.71 (4H, s, N–CH2); 7.25-7.35 (10Н, m, 2С6Н5);
6.62 (2Н, br. s, NH2)
4c
1600
1590
3410,
3310
3420,
3310
1110,
1070
1120,
1090,
1065
2.50
2.58
3.40
3.41
4.80
4.79
7.14
7.10
7.20-7.44 (10Н, m, 2C6H5); 7.25 (2Н, br. s, NH2)
3.65–3.70 (8Н, m, morpholino); 6.13 (2H, br. s, NH2)
4d
4e
6a
1595
1720
3465,
3255
1095
2.66
2.55
3.45
3.41
4.80
4.88
7.0
7.27–7.89 (5H, m, C6H5); 8.12 (2H, br. s, NH2)
(2130)
1280*,
1190*,
1130,
1100,
1050
1.38 (3H, t , J = 7.2, CH2CH3); 4.27 (2H, q, J = 7.2, CH2CH3)
6b
6c
1620
1635
(2115)
(2120)
1120,
1085
2.59
2.54
3.52
3.46
4.93
4.92
4.67 (4Н, s, N–CН2); 7.20-7.36 (11Н, m, НPy,С6Н5)
7.22-7.45 (11Н, m, НPy, С6Н5)
1120,
1090

TABLE 2 (continued)
1
2
3
4
5
6
7
8
9
6d
1625
(2115)
1120,
1070
2.64
3.51
4.94
7.33
3.66-3.70 (8Н, m, ОСН2, NCH2)
6e
1625
1680
(2110)
—
1110
2.50
2.50
3.38
3.08
4.76
4.86
7.26
7.18
7.07-7.62 (5H, m, C6H5)
0.79 (3Н, t , J = 7.2, ОСН2СН3); 3.55 (2Н, q, J = 7,2, ОСН2СН3);
7.48-7.62 (15Н, m, С6Н5)
7а
1255*,
1170*,
1120,
1080
7b
1620
1640
1605
1600
—
—
—
—
1100,
1080
2.50
2.47
2.55
2.53
3.10
3.21
3.20
3.15
4.87
5.04
4.99
4.96
4.08 (4Н, s, N–СН2); 7.00-7.67 (26Н, m, НPy, С6Н5)
6.67-7.69 (26Н, m, НPy , С6Н5)
7c
1120,
1070
7d
1115,
1085
7.15
3.05 (4Н, s, N–СН2); 3.42 (4Н, s, О–СН2); 7.44-7.64 (15Н, m, С6Н5)
6.87-7.85 (21Н, m, НPy, С6Н5)
7e
1120,
1080
_______
* Bands for ester С−О−С.

The diazotization of 3-aminothieno[2,3-b]pyridines 4a-e was carried out in acetic acid in the presence of
conc. sulfuric acid. Diazonium salts 5a-e obtained in solution were used for nucleophilic substitution by means
of sodium azide immediately after eliminating excess nitrous acid.
O
O
_
+
N2
HSO4
N3
O
O
R
NaNO2
H2SO4
NaN3
4a–e
S
S
R
N
N
6a–e
5a–e
5, 6 a R = OEt, b R = N(CH2Ph)2, c R = NPh2, d R = N(CH2CH2)2O, e R = Ph
The resultant 3-azidothieno[2,3-b]pyridines 6a-e are colorless or light-yellow compounds, which
decompose upon storage (Table 1).
The IR spectral data provide the most helpful information for establishing the structure of
3-azidothieno[2,3-b]pyridines 6 (Table 2). The substitution of the amino groups at C(3) in thieno[2,3-b]pyridines
4 by azido groups leads to the disappearance of the two N–H stretching bands and a shift in the carbonyl group
band toward higher frequencies: by 60 cm-1 for ester 6a, by 25-65 cm-1 for amides 6b-d, and by 30 cm-1 for
ketone 6e. The characteristic band for the azido group appears at 2130-2110 cm-1. The 1H NMR spectra of azides
6 lack the amino group proton signals found in the spectra of starting thieno[2,3-b]pyridines 4 (Table 2).
The reaction of 3-azidothieno[2,3-b]pyridines 6 with triphenylphosphine was carried out in benzene.
This reaction proceeds with the liberation of nitrogen. The cessation of nitrogen liberation indicates the end of
this reaction.
Ph
Ph
Ph
+
O
_
P
N
O
PPh3
6a–e
S
R
N
7a–e
7 a R = OEt, b R = N(CH2Ph)2, c R = NPh2, d R = N(CH2CH2)2O, e R = Ph
The resultant iminophosphoranes 7a,c,e are yellow, while 7b and 7d are colorless. These products form
crystals with high melting points (Table 1). The presence of the heteroaromatic substituent at the nitrogen atom
in triphenylphosphoranes 7 provides for their resistance to the action of water. Phosphoranes 7 are insoluble in
alkanes and diethyl ether but have moderate solubility in ethanol and good solubility in DMF and DMSO.
In comparison to the IR spectra of the corresponding azides, the spectra of iminophosphoranes 7
(Table 2) lack the azido group band and show stronger C–Har stretching bands. The structure of
iminosphosphoranes 7 was confirmed by their 1H NMR spectra.
An X-ray diffraction structural analysis was carried out for iminophosphorane 7e which has a benzoyl
substituent at C(2) of the thiophene system (Fig. 1, Tables 3 and 4).
1604

Fig. 1. Projection of the structure of 7e.
The steric strain in the O(2)–C(11)–C(2)–C(1)–N(2)–P(1) fragment leads to significant distortions of the
bond angles at these atoms. Thus, the C(24)–P(1)–C(30), N(2)–P(1)–C(24), and N(1)–P(1)–C(30) bond angles
are expanded to 113.59, 115.74, and 114.34°, respectively, probably due to the repulsion of the
TABLE 3. Bond Lengths (d) in 7e Obtained in an X-Ray Diffraction
Structural Analysis
Bond
S(1)−C(3)
d, Å
Bond
d, Å
1.723(3)
1.763(3)
1.575(2)
1.799(3)
1.814(3)
1.817(3)
1.404(4)
1.416(4)
1.231(3)
1.330(4)
1.346(3)
1.354(3)
1.403(4)
1.458(4)
1.432(4)
1.397(4)
1.394(4)
1.502(4)
1.374(4)
1.405(4)
1.495(4)
1.498(4)
1.376(4)
1.378(4)
1.373(4)
1.365(5)
1.357(5)
1.386(5)
1.379(4)
1.379(4)
1.377(5)
1.366(6)
1.368(6)
1.384(5)
1.382(4)
1.391(4)
1.375(5)
1.359(6)
1.370(6)
1.388(5)
1.386(4)
1.389(4)
1.381(5)
1.359(6)
1.364(6)
1.388(5)
C(12)−C(13)
C(13) −C(14)
C(14)−C(15)
C(15)−C(16)
C(16)−C(17)
C(18)−C(23)
C(18)−C(19)
C(19)−C(20)
C(20)−C(21)
C(21)−C(22)
C(22)−C(23)
C(24)−C(29)
C(24)−C(25)
C(25)−(26)
C(26)−C(27)
C(27)−C(28)
C(28)−C(29)
C(30)−C(35)
C(30)−C(31)
C(31)−C(32)
C(32)−C(33)
C(33)−C(34)
C(34)−C(35)
S(1)−C(2)
P(1)−N(2)
P(1)−C(24)
P(1)−C(30)
P(1)−C(18)
O(1)−С(9)
O(1)−C(10)
O(2)−C(11)
N(1)−C(4)
N(1)−C(3)
N(2)−C(1)
C(1)−C(2)
C(1)−C(7)
C(2)−C(11)
C(3)−C(7)
C(4)−C(5)
C(4)−C(8)
C(5)−C(6)
C(6)−C(7)
C(6)−C(9)
C(11)−C(12)
C(12)−C(17)
1605

TABLE 4. Bond Angles (θ) in 7e Obtained in an X-Ray Diffraction
Structural Analysis
Angle
θ, deg
Angle
θ, deg
91.16(13)
115.74(13)
114.34(13)
113.59(13)
104.81(13)
104.56(13)
101.74(13)
111.8(3)
115.2(3)
137.5(2)
130.9(2)
118.3(2)
110.8(2)
127.5(2)
112.5(2)
119.3(2)
126.5(3)
120.4(2)
113.1(2)
122.7(3)
117.2(3)
120.2(3)
121.9(3)
116.8(3)
120.7(3)
122.5(2)
116.9(2)
112.5(2)
130.6(2)
110.5(2)
122.4(3)
117.8(3)
119.7(2)
118.6(3)
124.0(3)
117.3(3)
120.8(3)
120.0(4)
120.1(3)
120.3(3)
120.1(3)
118.7(3)
123.4(3)
117.9(2)
120.9(4)
119.9(4)
120.1(4)
120.1(4)
120.3(4)
118.5(3)
124.4(2)
117.0(2)
120.9(4)
120.1(4)
120.2(4)
120.5(4)
119.8(4)
119.2(3)
119.5(2)
121.1(2)
119.8(3)
120.7(4)
120.1(4)
120.6(4)
119.6(3)
C(3)−S(1)−C(2)
N(2)−P(1)−C(24)
N(2)−P(1)−C(30)
C(24)−P(1)−C(30)
N(2)−P(1)−C(18)
C(24)−P(1)−C(18)
C(30)−P(1)−C(18)
C(9)−O(1)−C(10)
C(4)−N(1)−C(3)
C(1)−N(2)−P(1)
N(2)−C(1)−C(2)
N(2)−C(1)−C(7)
C(2)−C(1)−C(7)
C(1)−C(2)−C(11)
C(1)−C(2)−S(1)
C(11)−C(2)−S(1)
N(1)−C(3)−C(7)
N(1)−C(3)−S(1)
C(7)−C(3)−S(1)
N(1)−C(4)−C(5)
N(1)−C(4)−C(8)
C(5)−C(4)−C(8)
C(6)−C(5)−C(4)
C(5)−C(6)−C(7)
C(5)−C(6)−C(9)
C(7)−C(6)−C(9)
C(3)−C(7)−C(6)
C(3)−C(7)−C(1)
C(6)−C(7)−C(1)
O(1)−C(9)−C(6)
O(2)−C(11)−C(2)
O(2)−C(11)−C(12)
C(2)−C(11)−C(12)
C(17)−C(12)−C(13)
C(17)−C(12)−C(11)
C(13)−C(12)−C(11)
C(14)−C(13)−C(12)
C(15)−C(14)−C(13)
C(16)−C(15)−C(14)
C(15)−C(16)−C(17)
C(12)−C(17)−C(16)
C(23)−C(18)−C(19)
C(23)−C(18)−P(1)
C(19)−C(18)−P(1)
C(20)−C(19)−C(18)
C(21)−C(20)−C(19)
C(20)−C(21)−C(22)
C(21)−C(22)−C(23)
C(18)−C(23)−C(22)
C(29)−C(24)−C(25)
C(29)−C(24)−P(1)
C(25)−C(24)−P(1)
C(26)−C(25)−C(24)
C(27)−C(26)−C(25)
C(26)−C(27)−C(28)
C(27)−C(28)−C(29)
C(24)−C(29)−C(28)
C(35)−C(30)−C(31)
C(35)−C(30)−P(1)
C(31)−C(30)−P(1)
C(32)−C(31)−C(30)
C(33)−C(32)−C(31)
C(32)−C(33)−C(34)
C(33)−C(34)−C(35)
C(30)−C(35)−C(34)
C(24)···C(29) and C(30)···C(35) benzene rings and C(1)–O(1) carbonyl group. This repulsion would also
account for the expansion of the bond angle at N(2) (by 17.5°) relative to the standard value for sp2-hybridized
nitrogen.
The phosphorus atom is found in an sp3-hybridized state: the mean value of the bond angles at the
phosphorus atom is 109.12°.
The phenyl ring of the benzoyl substituent is extruded from the plane of the heterocyclic system by 65.2°
as the result of repulsion of the sulfur atom and hydrogen atom at C(17).
The S(1)–C(3) bond (1.723 Å) is shortened relative to the S(1)–C(2) bond (1.763 Å) due to displacement
of an electron pair of this sulfur atom toward the pyridine ring with π-electron deficiency.
1606

EXPERIMENTAL
The UV spectra were taken in ethanol on Specord UV-vis and Specord M-40 spectrometers at
200-700 nm in quartz cells; the path length was 10 mm. The IR spectra were taken on Specord-71 and UR-20
spectrometers at 3600-650 cm-1 using NaCl and KBr plates. The crystalline compounds were taken in vaseline
1
mull. The H NMR spectra were taken on a Bruker WM-250 spectrometer at 250 MHz in DMSO-d6 with TMS
as the internal standard.
N,N-Diphenyl-3-amino-4-methoxymethyl-6-methylthieno[2,3-b]pyridine-2-carboxamide (4c). 10%
aq. KOH (5.6 ml, 10 mmol) was added to a suspension of 3-cyano-2(1H)-pyridinethione 1 (1.94 g, 10 mmol) in
DMF (20 ml). Then, N,N-diphenylchloracetamine (2c) (2.46 g, 10 mmol) was added with stirring. The mixture
was maintained for 10-15 min at room temperature. Then, an additional 10% aq. KOH (5.6 ml, 10 mmol) was
added and the reaction mixture was stirred for 6 h at 80-85°C. After cooling of the reaction mixture, the
precipitate formed was separated, washed consecutively with water and 1:1 ethanol–water, and dried in the air.
The filtrate was diluted with a two-fold volume of water and the flocculent precipitate was separated, washed
with water, and dried. The product was recrystallized from ethanol–DMF. The total yield was 3.63 g (90%).
Products 4b,d,e were similarly obtained.
N,N-Diphenyl-3-azido-4-methoxymethyl-6-methylthieno[2,3-b]pyridine-2-carboxamide
(6c).
Compound 4c (2.02 g, 5 mmol) was dissolved in glacial acetic acid (12 ml) and conc. sulfuric acid (0.6 ml) was
added. The reaction mixture was cooled in an ice bath to 5-9°C and then, a solution of NaNO2 (0.48 g, 7 mmol)
in water (2 ml) was added slowly in small portions. The mixture was stirred for 20 min and then, the excess
nitrous acid was neutralized by adding urea (monitored by iodine–starch paper). A solution of NaN3 (0.46 g,
7 mmol) in water (2 ml) was added dropwise over 10 min. The mixture was stirred for 1 h and then slowly
poured into water containing finely ground ice. The precipitate of azide 6c was separated, washed on the filter
with cold water until the wash water was neutral, and dried over conc. sulfuric acid in the absence of light to
give 2.08 g (97%) of 6c.
3-Azidothieno[2,3-b]pyridines 6a,b,d were similarly obtained.
(2-Benzoyl-4-methoxymethyl-6-methylthieno[2,3-b]pyridin-3-yl)iminotriphenylphosphorane (7e).
Triphenylphosphine (2.62 g, 10 mmol) was added to a solution of 3-azidothieno[2,3-b]pyridine 6e (3.38 g,
10 mmol) in benzene (100 ml). The reaction mixture was stirred until gas bubbles were no longer observed and
left overnight. The precipitate formed was filtered off, washed with benzene, and dried in the air. The filtrate was
evaporated in vacuum and the residue was triturated with diethyl ether. The crystals formed were filtered off,
washed with benzene, and dried in the air. The product was recrystallized from ethanol–DMF. The total yield of
7e was 3.2 g (56%). Yellow monoclinic crystals of 7e were obtained by crystallization from ethanol. The unit
cell parameters are as follows: a = 9.869(2), b = 16.644(3), c = 17.853(4) Å, β = 92.58(3)°, V = 2929.6(10) Å3,
space group P2(1)/n, Z = 4. The unit cell parameters and intensities of 2293 independent reflections were
measured on a CAD-4 automatic diffractometer using MoKα radiation, β-filter, and θ/2θ-scanning to 2θmax
=
44.6°. The structure was deciphered by the direct method using the SHELXTL program package [6] and refined
anisotropically for the nonhydrogen atoms and isotropically for the hydrogen atoms to R1 = 0.0268 and Rw =
0.0709.
Products 7a,c were similarly obtained.
(N-Morpholyl-2-carbamoyl-4-methoxymethyl-6-methylthieno[2,3-b]pyridin-3-yl)iminotriphenyl-
phosphorane (7d). Triphenylphosphine (2.62 g, 10 mmol) was added to a solution of 3-azidothieno[2,3-b]-
pyridine 6d (3.47 g, 10 mmol) in benzene (100 ml). The reaction mixture was stirred until there was no further
liberation of gas and left overnight. The mixture was then evaporated in vacuum by 4/5 and hexane (10 ml) was
added. The crystals formed were filtered off, washed with hexane, and dried in the air. The product was
recrystallized from ethanol–DMF. The total yield of 7d was 3.66 g (63%).
Product 7b was similarly obtained.
1607

This work was carried out with the financial support of the Russian Basic Research Fund (RFFI) (Grant
No. 03-03-96636).
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