Phenylfurylthieno[2,3-b]pyridyl-methanes. synthesis and reactions of the furan ring transformation

Article abstract of DOI:10.1007/s10593-009-0401-9

Triarylmethane derivatives with various substituents, phenyl, 5-methyl-2-furyl, and 3-acylamino-thieno[2,3-b]pyrid-2-yl have been obtained for the first time. The behavior of these compounds under protolytic conditions has been studied. It was shown that

Full text of DOI:10.1007/s10593-009-0401-9

Chemistry of Heterocyclic Compounds, Vol. 45, No. 9, 2009
PHENYLFURYLTHIENO[2,3-b]PYRIDYL-
METHANES. SYNTHESIS AND REACTIONS
OF THE FURAN RING TRANSFORMATION
D. Yu. Kosulina1, V. K. Vasilin1, T. A. Stroganova1,
E. A. Sbitneva1, A. V. Butin1, and G. D. Krapivin1*
Triarylmethane derivatives with various substituents, phenyl, 5-methyl-2-furyl, and 3-acylamino-
thieno[2,3-b]pyrid-2-yl have been obtained for the first time. The behavior of these compounds under
protolytic conditions has been studied. It was shown that the character of the protection of the amino
group of the thienopyridine fragment affects the type of transformation of the furan ring.
Keywords: 3-amino-2-benzoylthieno[2,3-b]pyridines, N-[2-(2,5-dioxo-1-phenylhexyl)thieno[2,3-b]pyrid-
3-yl]benzamides, (phenyl)(2-acylaminothieno[2,3-b]pyrid-2-yl)carbinols, (phenyl)(5-methylfur-2-yl)-
(2-acylaminothieno[2,3-b]pyrid-2-yl)methanes, 4-(3-phenyl-1H-pyrrolo[2',3':4,5]thieno[2,3-b]pyrid-2-yl)-
butan-2-ones, alkylation, acylation, reduction, transformation of the furan ring.
Derivatives of benzylfuran of type A containing a functional group X in the ortho position of the
benzene ring, are attractive as intermediates for obtaining the most varied condensed carbo- and heterocyclic
compounds [1]. Depending on the character of substituent X two routes of conversion are possible in principle:
1) closing of the hetero- or carbocycle between the furan and benzene rings with the formation of a product of
type B [2, 3] or 2) cleavage of the heterocycle and annelation of the benzene nucleus with the formation of a
product of type C (Scheme 1).
Scheme 1
O
R1
R2
R1
R1
R2
X
Y
2
z
R4
1
R4
R4
R2
O
O
R3
R3
R3
A
B
C
_______
* To whom correspondence should be addressed, e-mail: organics@kubstu.ru.
1Kuban State University of Technology, Krasnodar 350072, Russia.
__________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1380-1394, September, 2009.
Original article submitted April 1, 2008; revision submitted July 30, 2008.
0009-3122/09/4509-1105©2009 Springer Science+Business Media, Inc.
1105

From the second route, named by us "furan ring opening – heterocyclic ring closing" [4], derivatives of
benzofuran [5, 6], indole [4, 7], isochromone [8], isoquinolone [9, 10], benzopyran [11], and cinnoline [12] were
obtained. In particular, derivatives of indole of type C (Z = NTs) were synthesized by us starting from ortho-
acylaminoarenes D (Scheme 2), converted through carbinols E into compounds of type A (X = NHTs).
Scheme 2
H
H
R1
R2
N
Ts
N
Ts
A
C
O
OH
R3
R3
D
E
The problem of the present work was to show the possibility of using analogs of compounds A with a
heterocyclic acylamino-substituted fragment in transformations according to pathway 2. To solve this, readily
available analogs of compounds D were selected as starting materials, viz. derivatives of 2-acyl-3-amino-
thieno[2,3-b]pyridine 1 obtained by the Torp reaction from the appropriate 3-cyanopyridine-2-thiones [13].
We showed in [14] that the direct conversion of amino ketones 1 into the corresponding alcohols by the
action of NaBH4 was not possible. In their place derivatives of 6-phenyl-7,12-dithia-1,5,8-triaza-
indeno[1,2-a]fluorene were formed, products of intermolecular dimerization accompanied by the elimination of
benzonitrile. Consequently acyl protection of the amino group of compounds 1 was carried out before reduction
of the carbonyl group. It is known [4, 7] that such protection is also necessary at the following stage of
alkylation of the furan by carbinols. The acylamino derivatives 2 were obtained in high yield (70-95%, Table 1)
by boiling amino ketones 1 with the appropriate acid chlorides of carboxylic acids in dioxane or toluene by the
procedure of [15] (Scheme 3).
Scheme 3
R2
R2
O
O
O
R
N
R
N
R
N
NH
NH2
R2
NH
3
Ph
Ph
O
Ph
O
NaBH4
EtOH
Cl
5
R1
R1
S
R1
OH
S
S
1
3a–j
1a–e
2a–j
1 а R = R1 = Me, b R = CH2OMe, R1 = Me, c R = R1 = Ph, d R = 5-methyl-2-furyl, R1 = Ph,
e R = C6H4Br-4, R1 = Ph; 2, 3 a–e R2 = Ph, a R = R1 = Me, b R = CH2OMe, R1 = Me,
c R = R1 = Ph, d R = 5-methyl-2-furyl, R1 = Ph, e R = C6H4Br-4, R1 = Ph, f R = R1 = Me,
R2 = 2-furyl, g R = CH2OMe, R1 = Me, R2 = 2-furyl, h R = CH2OMe, R1 = Me,
R2 = 2-thenoyl, i R = R1 = R2 = Me, j R = CH2OMe, R1 = R2 = Me
We note that amino ketones 1 do not react with carboxylic acid anhydrides. For example, boiling
compounds 1 with an excess of acetic anhydride for 5-6 h does not lead to the formation of appreciable
quantities of products of type 2.
The acyl derivatives 2a-j are colorless crystalline substances with sharp melting points (Table 1). In the
IR spectra of these compounds (Table 2) there are two narrow intense absorption bands in the region of
1630-1635 and 1670-1680 cm-1 corresponding to the stretching vibrations of the amide and ketone carbonyl
groups. A broad absorption band is also present in the region of 3230-3360 cm-1 corresponding to the stretching
1106

1
vibrations of the amide N–H bond. In the H NMR spectra of compounds 2 (Table 3), together with signals for
HPh and HHet, there are signals for the protons of the introduced N-acyl fragment and a one-proton singlet for the
NHCO group.
The formation of cation Φ1 at the first stage of fragmentation (electron impact, 70 eV) is general for the
molecular ions of compounds 1, 2 (Scheme 4). This has maximum intensity in the mass spectra of amino
ketones 1, but in the spectra of their acyl derivatives 2 is 60-80% of maximum, which in these cases is the
intensity of the peak of cation R2CO+.
Scheme 4
R2
NH
O
H
.
+
.
R
+
NH2
N
.
.
– R2CO
O
+
Ph
O
Ph
– Н
Ph
R1
N
S
S
O
S
M (2)
Ф1
M (1)
.
– PhCO
NH
.
+
S
Ф2
The second step of the fragmentation, the thermodynamically unfavorable process of removing a PhCO
radical from cation Φ1, leads to the odd-electron fragment Φ2.
Reduction of the carbonyl group of compounds 2 with sodium borohydride in ethanol at 40-60oC leads
to the corresponding alcohol 3 in 75-90% yield (Scheme 3, Table 1). Products 3a-j were colorless crystalline
substances with sharp melting points. In the IR spectra of alcohols 3 there were bands for the stretching
vibrations of the OH group at 3381-3245 cm-1, but the band for the amide NH group at 3380-3417 cm-1 was
displaced towards long wave in comparison with the analogous band in the spectra of the corresponding ketones
2. The 1H NMR spectra also indicate the presence of the CH–OH grouping, the protons of which have coupling
constants ~3.0-4.5 Hz (Table 3). The singlet signal of the CONH group is found at low field in the region of
9.4-10.1 ppm. Reduction of the ketone group to alcohol leads to the formation of an asymmetric center in the
alcohol molecules, which is clearly displayed in the spectra of compounds 3b,g,h,j, having a CH2OCH3 group.
The prochiral methylene protons in the alcohol molecules become diastereotopic and resonate as pairs of one-
proton doublets with a common geminal coupling constant J = 14.5 Hz.
The molecular ions of alcohols 3 are extremely unstable and are not found when using standard values
for the energy of the ionizing electrons. The first step of their fragmentation, the rearrangement with elimination
of a water molecule, is common to all the series of compounds investigated. The [M-18] cation-radical formed is
decomposed in two directions, with cleavage of molecules of R2CN and R2NCO. When R2 = Alk (compounds
3i,j) simple removal of radical R2 occurs in parallel.
Furylhetarylmethanes 4a-i were obtained by the alkylation of 2-methylfuran with alcohols 3a-i by
boiling equimolar quantities of reactants in dioxane (3-12 h) in the presence of catalyst, which was a mixture of
70% perchloric acid, acetic anhydride, and glacial acetic acid (Scheme 5).
The carrying out of the reaction with the aid of the indicated catalytic system makes possible, even on
extended contact with the acid catalyst, a reduction in resinification of the furan substrate and prevent side
conversions of both the initial methylfuran and of the reaction products 4 containing the acidophobic furan ring.
1107

Scheme 5
R2
NH
2
O
R
N
HClO4
dioxane
4
Ph
5
3a–i
+
Me
O
R1
O
S
Me
4а–i
Products 4, isolated from the reaction mixture in 65-95% yield, were colorless crystalline compounds, soluble in
methylene chloride, ethyl acetate, and alcohol (Table 1).
1
In the H NMR spectra of methanes 4 (Table 3) signals were present for the two β-protons of the furan
ring as a pair of doublets at 6.0-6.1 ppm with coupling constant typically 3J = 2.8-3.3 Hz and a singlet signal for
the protons of the methyl group in position 5 of the furan fragment. The methine proton at the central
sp3-hybridized carbon atom resonates as a singlet in the 5.8-6.0 ppm region. The diastereotopic protons of the
methylene unit of the CH2OCH3 group of compounds 4b,g,h, as in the spectra of the corresponding alcohols
3b,g,h, also resonate as a pair of one-proton doublets with 2J = ~14 Hz.
The molecular ions of methanes 4 had low intensities, but for compounds 4b,g, having a methoxymethyl
fragment, were generally absent. Peaks of cation radicals [M-CH3OH] had the greatest value of m/z. The typical
sequence of fragmentation reactions of the molecular ion (or [M-CH3OH] ion) was separation of a R2CO radical
and subsequent rearrangement with extrusion of a ketene molecule. We note in all mass spectra of this series of
compounds the presence of a characteristic peak of the (phenyl)(5-methyl-2-furyl)-methyl cation with m/z 171.
Investigation of the behavior of methanes 4 in acidic medium (acetic acid with added perchloric acid or
ethanol saturated with dry HCl) showed that the character of the proceeding reactions depended on the type of
acyl substituent at the nitrogen atom. Extended boiling (up to 8 h) of compounds 4b-d,g,h, having an aryl or
hetaryl substituent R2, leads only to the products of hydrolytic breakdown of the furan ring 5a-e, without the
formation of recyclization products of type 6 (Scheme 6). It should be noted that in the reaction mixture an
equilibrium was established between the initial furans 4 and diketones 5 significantly more rapidly in acetic acid
than in ethanol.
Scheme 6
R2
O
Me
R
N
O
NH
+ H2O
–H2O
4b–d,g,h
O
S
Ph
R1
R2
O
O
R
5a–e
N
Me
R1
N
S
6
5 a R = CH2OMe, R1 = Me, R2 = Ph, b R = R1 = R2 = Ph, c R = 5-methyl-2-furyl, R1 = R2 = Ph,
d R = CH2OMe, R1 = Me, R2 = 2-furyl, e R = CH2OMe, R1 = Me, R2 = 2-thenoyl
1108

The fact of the equilibrium between the initial and final reaction products was confirmed by us
experimentally. Under the same conditions diketone 5b forms an analogous equilibrium mixture (~2:3) of
compounds 4c and 5b after a short time (~1 h), according to data of 1H NMR spectra.
TABLE 1. Physicochemical Characteristics of the Synthesized Compounds
Found, %
——————
Calculated, %
Com-
pound
Empirical
formula
Yield,
%
mp, °С
С
Н
N
2c
2d
2e
2h
2i
C33H22N2O2S
C32H22N2O3S
C33H21BrN2O2S
C22H18N2O3S2
C18H16N2O2S
C19H18N2O3S
С33Н24N2O2S
С32Н24N2O3S
С33Н23BrN2O2S
С21Н18N2O3S
С22Н20N2O3S2
C18H18N2O2S
C19H20N2O3S
C28H24N2O2S
C29H26N2O3S
C38H28N2O2S
C37H28N2O3S
C38H27BrN2O2S
77.55
77.62
74.63
74.69
67.33
67.24
62.67
62.54
66.75
66.64
64.47
64.39
77.43
77.32
74.52
74.40
67.13
67.01
66.57
66.65
62.33
62.24
66.27
66.23
64.07
64.02
74.25
74.31
72.22
72.17
79.27
79.14
4.33
4.34
4.25
4.31
3.50
3.59
4.37
4.29
5.06
4.97
4.98
5.12
4.58
4.72
4.81
4.68
3.99
3.92
4.91
4.79
4.68
4.75
5.66
5.58
5.56
5.66
5.21
5.35
5.52
5.43
4.85
4.89
5.53
5.49
5.54
5.44
4.58
4.75
6.54
6.63
8.77
8.64
7.82
7.90
5.39
5.46
5.56
5.42
4.59
4.74
7.50
7.40
6.68
6.60
8.66
8.58
7.75
7.86
6.30
6.19
5.93
5.80
4.71
4.86
153-154
185-186
203-204
169-170
161-162
166-167
257-258
200-201
222-223
137-138
165-166
178-179
133-134
229-230
204-205
198-199
218-219
85
60
80
70
50
45
90
70
90
85
80
73
72
80
75
71
60
65
2j
3c
3d
3e
3f
3h
3i
3j
4а
4b
4c
4d
4e
76.64
76.53
4.76
4.86
4.86
4.82
>135
(decomp.)
69.73
69.62
4.02
4.15
4.37
4.27
4f
C26H22N2O3S
C27H24N2O4S
C27H24N2O3S2
C23H22N2O2S
C29H28N2O4S
C38H30N2O3S
C37H30N2O4S
70.71
70.57
68.57
68.62
66.49
66.37
70.65
70.74
69.69
69.58
76.78
76.74
5.13
5.01
5.01
5.12
4.84
4.95
5.78
5.68
5.55
5.64
4.99
5.08
4.97
5.05
6.40
6.33
5.83
5.93
5.81
5.73
7.26
7.17
5.69
5.60
4.63
4.71
229-230
144-145
197-198
187-188
132-133
169-170
181-182
95
80
82
30
27
32
25
4g
4h
4i
5a
5b
5c
74.33
74.23
4.81
4.68
5d
5e
7a
7b
C27H26N2O5S
C27H26N2O4S2
С21Н20N2OS
C22H22N2O2S
66.22
66.10
63.93
64.01
72.49
72.38
5.23
5.34
5.27
5.17
5.91
5.79
5.64
5.71
5.59
5.53
7.94
8.04
121-122
171-172
178-179
35
40
67
40
>230
(sublimed)
69.88
69.81
5.77
5.86
7.48
7.40
1109

TABLE 2. IR Spectra of the Synthesized Compounds
Com-
pound
Com-
pound
IR spectrum, ν, cm-1
IR spectrum, ν, cm-1
2c
3230 (NH), 1645 (C=O)
3369 (NH), 1676 (C=O)
4c
3272 (NH), 1652 (C=O)
2d
4d
3267 (NH), 3147-3029
(C–H arom.), 1645 (C=O)
2e
2h
2i
3209 (NH), 1651 (C=O)
4e
4f
3636–3100 (NH),
3057 (C–H arom.), 1665 (C=O)
3354 (NH), 1666 (C=O),
1625 (C=O)
3471–3150 (NH),
3028 (C–H arom.), 1650 (C=O)
3245 (NH), 1662 (C=O),
1645 (C=O)
4g
4h
3251 (NH), 3058 (C–H arom.),
1672 (C=O)
2j
3431, 3134 (NH), 1697 (C=O),
1635 (C=O)
3286 (NH), 3093-3027
(C–H arom.), 1637 (C=O)
3c
3232 (OH), 1630 (C=O)
4i
3272 (NH), 1654 (C=O)
3d
3380 (ОН), 1647 (С=О)
5a
3330 (NH), 1710 (C=O ketone),
1668 (С=О amide)
3e
3384 (OH), 3217, 3185 (NH),
1626 (C=O)
5b
3423 (NH), 1716 (C=O ketone),
1701 (C=O ketone),
1682 (С=О amide)
3f
3245 (NH), 1655 (C=O)
5c
5d
5e
7a
7b
3305 (NH), 1710 (C=O ketone),
1647 (С=О amide)
3h
3i
3240 (ОН), 1633 (С=О)
3270 (NH), 1714 (C=O ketone),
1673 (С=О amide)
3280–3120 (br. peak,
NH and ОН), 1652 (C=O)
3373 (NH), 1701 (C=O ketone),
1655 (С=О amide)
3j
3384 (OH), 3230, 3185 (NH),
1654 (C=O)
3262 (NH), 1715 (C=O)
4а
4b
3278 (NH), 3122-3093
(C–H arom.), 1648 (C=O)
3485 (NH), 1712 (C=O)
3278 (NH), 3122-3062
(C–H arom.), 1654 (C=O)
Diketones 5a-e were colorless crystalline substances (Table 1). Bands were present in the IR spectra of
these compounds for the stretching vibrations of three carbonyl groups, two ketones at 1701-1716 and an amide in
the region of 1647-1682 cm-1 (Table 2). In the 1H NMR spectra there were two triplet signals for methylene protons
at 2.6-2.9 ppm having a vicinal coupling constant 3J = 5.8-6.4 Hz, and a singlet signal for the protons of the acetyl
group at 2.0-2.1 ppm (Table 3). Formally the diastereotopic protons of the methylene unit of the methoxymethyl
group of compounds 5a,d,e resonate in NMR spectra as homotopic as a two-proton singlet at 4.7-4.8 ppm. It is
possible that this is due to a rapidly proceeding inversion of the asymmetric center as a result of keto-enol
tautomerism involving the hydrogen atom of the methine unit and the carbonyl group neighboring it.
The molecular ions of compounds 5 are unstable and are not confirmed in the mass spectra (Table 4).
They are decomposed by two routes (Scheme 7) at the one bond between the methine carbon atom and the
neighboring carbonyl group, which indicates the localization of charge and spin precisely on the oxygen atom of
the "inner" carbonyl group.
Scheme 7
.
+
NHCOPh
O
R
.
NHCOPh
+
NHCOPh
Ph
Me
Ph
+
S
R1
N
S
S
O
Ph
[М – 99]
[М – 98]
M
1110

TABLE 3. 1H NMR Spectra of the Synthesized Compounds
Com-
pound
Chemical shifts, δ, ppm, SSCC (J, Hz)
1
2
2c
6.95 (4Н, d, J = 7.3, о-Н 4-, 6-Ph); 7.11-7.60 (12Н, m, m-, p-Н 4-, 6-Ph, PhCO, PhCN);
7.75 (2Н, d, J = 6.8, o-H PhCO); 7.92 (1Н, s, Н-5); 8.30 (2Н, d, J = 7.8, o-H PhCON);
9.56 (1Н, s, NH)
2d
1.81 (3Н, s, СН3); 6.09 (1Н, d, J = 2.9, H-4 methylfuryl);
7.02 (1Н, d, J = 2.9, H-3 methylfuryl); 7.25-7.65 (11Н, m, Н arom);
7.78 (2Н, d, J = 2.8, o-H PhСОN); 8.13 (1H, s, H-5); 8.30 (2Н, d, J = 8.3, o-H PhСO);
10.14 (1Н, s, NH)
2e
6.96 (2Н, d, J = 7.3, o-H C6H4Br-4); 7.22 (2Н, t, J = 8.1, m-H 6-Ph);
7.30-7.46 (9Н, m, Н arom); 7.55 (2Н, d, J = 7.3, m-H C6H4Br-4);
7.74 (2Н, d, J = 7.3, m-H PhCO); 7.95 (1H, s, H-5); 8.30 (2Н, d, J = 7.3, o-H PhCON);
9.70 (1Н, s, NH)
2h
2.50 (3H, s, 4-CH3); 3.32 (3H, s, OCH3); 4.92 (2H, s, OCH2);
7.10 (1Н, t, J = 3.9, H-3 thenoyl); 7.32-7.49 (5Н, m, 2 m-Н, p-H PhCO, H-5, H-4 thenoyl);
7.57 (1Н, d, J = 3.4, H-5 thenoyl); 7.77 (2Н, d, J = 7.8, o-H PhCON); 10.24 (1H, s, NH)
2i
1.50 (3H, s, CH3CO); 2.57 (3Н, s, 4-CH3); 2.62 (3H, s, 6-CH3); 7.19 (1H, s, H-5);
7.52 (2Н, t, J = 7.3, C6H5); 7.62-7.74 (3Н, m, C6H5); 9.76 (1H, s, NH)
2j
3c
3d
1.52 (3H, s, CH3CO); 2.63 (3H, s, 6-CH3); 3.95 (3H, s, OCH3); 4.92 (2Н, s, OCH2);
7.43 (1H, s, Н-5); 7.52 (2Н, t, J = 8.1, C6H5); 7.60-7.70 (3Н, m, C6H5); 9.82 (1H, s, NH)
6.12 (1Н, d, J = 4.4, CHOH); 6.44 (1Н, d, J = 4.4, OH); 7.06-7.54 (18Н, m, Н arom);
7.74 (1H, s, H-5); 8.15-8.26 (2Н, m, Н PhСО); 9.54 (1H, s, NH)
1.96 (3H, s, CH3 methylfuryl); 6.00 (1Н, d, J = 4.39, СНOH); 6.22 (1Н, br. s, ОН);
6.50 (1Н, d, J = 2.4, Н-4 methylfuryl); 6.88 (1Н, d, J = 2.4, Н-3 methylfuryl);
7.25 (2Н, d, J = 7.3, m-H PhCON); 7.36-7.65 (9H, m, Н arom);
7.80 (2Н, d, J = 7.3, o-H PhCH)); 7.96 (1Н, s, Н-5); 8.20 (2Н, d, J = 6.8, m-H 6-Ph);
9.97 (1H, s, NH)
3e
3f
6.13 (1Н, d, J = 4.4, СНOH); 6.50 (1Н, d, J = 4.4, ОН); 7.15-7.56 (17Н, m, H arom);
7.76 (1Н, s, Н-5); 8.19 (2Н, d, J = 6.6, m-H PhCO); 9.62 (1H, s, NH)
2.47 (6Н, s, 4-, 6-СН3); 6.02 (1Н, d, J = 4.4, CHOH); 6.36 (1Н, d, J = 4.4, OH);
6.72 (1H, s, H-3 furoyl); 7.02 (1H, s, H-5); 7.17-7.34 (4Н, m, 3Н Ph, H-4 furoyl);
7.37 (2Н, d, J= 6.6, o-H arom); 7.95 (1H, s, H-2 furoyl); 9.97 (1Н, br. s, NH)
2.6 (3H, s, 6-CH3); 3.27 (3H, s, OCH3); 4.74 (1H, d, J = 14.4, OCH2);
4.76 (1H, d, J = 14.4, OCH2); 6.03 (1Н, d, J = 2.9, CHOH); 6.51 (1H, d, J = 2.9, OH);
7.21-7.41 (7Н, m, 5 Н Ph, H-5, Н-4 thenoyl); 7.91 (1Н, d, J = 4.4, H-3 thenoyl);
7.96 (1H, d, J = 3.4, H-5 thenoyl); 10.04 (1H, s, NH)
3h
3i
3j
2.03 (3H, s, CH3CO); 3.35 (6Н, s, 4-, 6-CH3); 5.98 (1H, d, J = 3.7, CHOH);
6.36 (1H, d, J = 3.7, OH); 7.00 (1H, s, H-5); 7.2 -7.4 (5Н, m, C6H5); 9.51 (1H, s, NH)
2.04 (3H, s, CH3CO); 2.55 (3Н, s, 6-CH3); 3.35 (3H, s, OCH3);
4.75 (1Н, d, J = 14.7, OCH2); 4.77 (1Н, d, J = 14.7, OCH2); 5.96 (1H, d, J = 3.7, CHOH);
6.40 (1H, d, J = 3.7, OH); 7.22-7.42 (6Н, m, C6H5, H-5); 9.44 (1H, s, NH)
4а
2.21 (3H, s, CH3 methylfuryl); 2.5 (6H, s, 4-, 6-CH3); 5.85 (1Н, s, PhCH);
6.01 (1H, d, J = 3.1, Н-4 methylfuryl); 6.06 (1H, d, J = 3.1, Н-3 methylfuryl);
7.06 (1Н, s, Н-5); 7.26 (2Н, d, J = 7.94, o-H PhCON); 7.30-7.35 (3H, m, o-, p-H PhCH);
7.51-7.65 (3Н, m, m-, р-Н PhCON); 7.97 (2Н, d, J = 7.9, m-Н PhCН); 10.13 (1H, s, NH)
4b
2.22 (3H, s, CH3 methylfuryl); 2.58 (3H, s, 6-CH3); 3.28 (3H, s, OCH3);
4.76 (1Н, d, J = 14.0, OCH2); 4.79 (1H, d, J = 14.0, OCH2); 5.86 (1Н, s, PhCH);
6.0 (1H, d, J = 2.8, Н-4 methylfuryl); 6.10 (1H, d, J = 2.8, Н-3 methylfuryl);
7.3 (6Н, m, C6H5, H-5); 7.52-7.66 (3Н, m, m-, р-Н PhCON);
7.97 (2Н, d, J = 7.4, o-Н PhCН); 10.02 (1H, s, NH)
4c
2.2 (3H, s, CH3 methylfuryl); 5.92 (1Н, s, PhCH); 6.04 (1H, d, J = 2.9, Н-4 methylfuryl);
6.10 (1H, d, J = 2.9, Н-3 methylfuryl); 7.02-7.55 (18Н, m, Н arom); 7.76 (1H, s, H-5);
8.19 (2Н, d, J = 6.4, о-Н PhCH); 9.65 (1H, s, NH)
4d
1.89 (3Н, s, СH3 methylfuryl-СН); 2.23 (3H, s, СН3 4-methylfuryl); 6.02 (1H, s, PhCH);
6.10 (2H, d, J = 2.9, methylfuryl-СH); 6.90 (2Н, d, J = 2.9, СН3 4-methylfuryl);
7.21-7.35 (5Н, m, Н arom); 7.41-7.59 (6H, m, H arom); 7.77 (2Н, d, J = 7.3, о-H PhCH);
7.97 (1Н, s, Н-5); 8.18 (2Н, d, J = 6.6, o-H PhCON); 10.08 (1H, s, NH)
4e
2.23 (3Н, s, СH3 methylfuryl); 5.94 (1H, s, PhCH); 6.02 (1H, d, J = 2.9, Н-4 methylfuryl);
6.10 (1H, d, J = 2.9, Н-3 methylfuryl); 7.22-7.58 (17Н, m, Н arom); 7.75 (1H, s, H-5);
8.18 (2Н, d, J = 5.9, о-H PhCON); 9.57 (1Н, s, NH)
1111

TABLE 3 (continued)
1
2
4f
2.2 (3H, s, CH3 methylfuryl); 2.5 (6H, s, 4,6-CH3); 5.81 (1Н, s, PhCH);
6.02 (1H, d, J = 2.9, Н-4 methylfuryl); 6.06 (1H, d, J = 2.9, Н-3 methylfuryl);
6.71 (1H, d, J = 3.5, Н-4 furoyl); 7.05 (1Н, dd, J = 3.5, J = 1.9, Н-3 furoyl);
7.20-7.38 (6Н, m, C6H5, H-5); 7.94 (1H, d, J = 1.9, Н-5 furoyl); 10.03 (1H, s, NH)
4g
2.22 (3H, s, CH3 methylfuryl); 2.6 (3H, s, 6-CH3); 3.27 (3H, s, OCH3);
4.74 (1H, d, J = 14.2, ОCH2); 4.78 (1H, d, J = 14.2, ОCH2); 5.82 (1Н, s, PhCH);
6.00 (1H, d, J = 2.9, Н-4 methylfuryl); 6.06 (1H, d, J = 2.9, Н-3 methylfuryl);
6.73 (1H, dd, J = 1.5, J = 3.9, Н-4 furoyl); 7.21-7.36 (7Н, m, 5Н Ph, H-5, Н-3 furoyl);
7.96 (1H, d, J = 1.5, Н-5 furoyl); 9.98 (1H, s, NH)
4h
2.22 (3H, s, CH3 methylfuryl); 2.6 (3H, s, 6-CH3); 3.27 (3H, s, OCH3);
4.76 (1H, d, J = 14.2, ОCH2); 4.78 (1H, d, J = 14.2, ОCH2); 5.82 (1Н, s, PhCH);
6.03 (1H, d, J = 2.9, Н-4 methylfuryl); 6.07 (1H, d, J = 2.9, Н-3 methylfuryl);
7.21-7.37 (7Н, m, C6H5, H-5, Н-4 thenoyl); 7.88 (1Н, d, J = 4.9, H-3 thenoyl);
7.97 (1H, d, J = 3.9, H-5 thenoyl); 10.08 (1H, s, NH)
4i
2.04 (6H, s, CH3CO, CH3 methylfuryl); 2.23 (6Н, s, 4-, 6-CH3); 5.77 (1Н, s, PhCH);
6.02 (1H, d, J = 3.2, Н-4 methylfuryl); 6.04 (1H, d, J = 3.2, Н-3 methylfuryl);
7.03 (1H, s, H-5); 7.21-7.38 (5Н, m, C6H5); 9.57 (1H, s, NH)
5a
2.07 (3H, s, CH3CO); 2.63 (2Н, t, J = 6.4, CH2CO); 2.82 (2Н, t, J = 6.4, СН2CH2CO);
3.3 (3H, s, OCH3); 4.76 (2H, s, OCH2); 5.71 (1H, s, PhCH);
7.31 (2H, d, J = 10.9, o-H PhCH); 7.55-7.71 (6Н, m, Н arom);
8.07 (2Н, d, J = 6.4, o-H PhCO); 10.09 (1H, s, NH)
5b
5c
2.07 (3H, s, CH3); 2.64 (2Н, t, J = 6.4, CH2CO); 2.84 (2Н, t, J = 6.4, СН2CH2CO);
5.74 (1H, s, CHPh); 7.02-7.58 (18Н, m, Н arom); 7.75 (1H, s, H-5);
8.20 (2Н, d, J = 6.4, o-H PhCO); 9.63 (1H, s, NH)
1.86 (1H, s, CH3 methylfuryl); 2.07 (3H, s, CH3CO); 2.65 (2Н, t, J = 5.9, CH2CO);
2.85 (2Н, t, J = 5.9, CH2CH2CO); 5.85 (1H, s, PhCH);
6.01 (1Н, d, J = 3.7, H-4 methylfuryl); 6.9 (1Н, d, J = 3.7, H-3 methylfuryl);
7.28-7.37 (2Н, m, o-H PhCH); 7.44-7.63 (9Н, m, Н arom);
7.87 (2Н, d, J = 6.6, o-H 6-Ph); 7.95 (1Н, s, H-5); 8.18 (2Н, d, J = 7.3, o-H PhСО);
10.07 (1H, s, NH)
5d
5e
2.07 (3H, s, CH3CO); 2.63 (2Н, t, J = 6.9, CH2CO); 2.81 (2Н, t, J = 6.9, СН2CH2CO);
3.28 (3H, s, OCH3); 4.74 (2H, s, OCH2); 5.69 (1H, s, PhCH);
6.76 (1Н, dd, J = 3.0, J = 1.5, H-4 furoyl); 7.25-7.42 (7Н, m, C6H5, H-5, H-3 furoyl);
8.00 (1H, d, J = 1.5, H-5 furoyl); 9.99 (1H, s, NH)
2.06 (3H, s, CH3CO); 2.63 (2Н, t, J = 5.9, CH2CO); 2.78 (2Н, t, J = 5.9, СН2CH2CO);
3.3 (3H, s, OCH3); 4.75 (2H, s, OCH2); 5.69 (1H, s, PhCH);
7.24-7.39 (7Н, m, C6H5, H-5, H-4 thenoyl); 7.92 (1Н, d, J = 4.4, H-3 thenoyl);
8.04 (1H, s, H-5 thenoyl); 10.09 (1H, s, NH)
7a
7b
2.11 (3H, s, CH3CO); 2.70 (6Н, s, 6-, 8-СН3); 2.92 (2Н, t, J = 7.3, CH2CH2CO);
3.12 (2Н, t, J = 7.3, CH2CO); 7.06 (1Н, s, Н-7); 7.25-7.29 (2Н, m, C6H5);
7.43-7.57 (3Н, m, C6H5); 11.46 (1H, s, NH)
2.13 (3H, s, CH3CO); 2.59 (3Н, s, 8-СН3); 2.94 (2Н, t, J = 6.6, CH2CH2CO);
3.09 (2Н, t, J = 6.6, CH2CO); 3.46 (3H, s, OCH3); 4.93 (2H, s, OCH2);
7.27-7.33 (2Н, m, C6H5); 7.45-7.53 (4Н, m, 3 Н arom, H-7); 11.33 (1H, s, NH)
As a result two reactions classical for mass spectrometry take place: dissociation with cleavage of an
acyl radical and the formation of a cation [M-99] and rearrangement with elimination of a molecule of ketene
and the formation of an odd-electron fragment [M-98]. The latter discards an acyl radical giving a stable
aminohetarylphenylmethyl cation [M-98-R2CO].
In difference to compounds 4b-d,g,h acetylamino derivative 4i under the same conditions is smoothly
converted into the corresponding recyclization and deacetylation product, a derivative of pyrrolothienopyridine
7a (Scheme 8). We note that a similar transformation, including the two reactions, was observed by us
previously for aromatic analogs [7, 16, 17]. The conversion 4i → 7a occurs in ethanol in a shorter time and with
a higher yield than in acetic acid.
1112

Compound 7b was obtained from the corresponding alcohol 3j on attempting to synthesize methane 4j
in dioxane in the presence of HClO4. A significant quantity of the recyclization and deacetylation product 7b
was rapidly formed in this way mixed with the intermediate methane 4j, isolation of which from the reaction
mixture was unsuccessful.
Scheme 8
O
H
1
R
N
Me
H+
7
4i, 3j
Ph
3
S
4
Me
N
5
7a,b
7 a R = Me, b R = CH2OMe
The pyrrolothienopyridines 7a,b were pale-yellow crystalline substances (Table 1). In the IR spectra
there was one narrow intense absorption band for the stretching vibrations of the ketonic carbonyl group at
1700-1712 cm-1 (Table 2). The methylene protons of the 3-oxobutyl substituent resonate as two triplets with
vicinal coupling constant 5.5-7.5 Hz at 2.9-3.1 ppm, and the protons of the terminal methyl group as a singlet
(2.1 ppm). The signal of the NH group proton is found at low field (11.3-11.5 ppm).
The molecular ions of compounds 7 were fairly stable (Table 4). The characteristic process of their
fragmentation is simple cleavage of the β-carbon–carbon bond in the 3-oxobutyl substituent which leads to a
cation of the "benzyl" type [M-57] (Scheme 9), possibly being isomerized into the even more stable ion Φ4.
Scheme 9
H
Me
Ph
+
N
Me
N
+
– MeCOCH2
M(7)
Ph
S
S
[M – 57]
Ф4
The intensity of the [M-57] ion in the spectrum was maximal, its fragmentation did not lead to any ion
comparable in stability. Competing with the [M-57] ion is the acetonyl cation with m/z 57, which has an
intensity less than 20%.
The conversions considered above of compounds 4 in acidic medium indicate that the character of the
protecting acyl group at the amine nitrogen determines the possibility or impossibility of carrying out
cyclization following protolytic opening of the furan ring. It is possible that in this case the difference in basicity
of benzoyl- and acetylamides is displayed, which on the whole leads to a different result for the reaction.
EXPERIMENTAL
1
The IR spectra were recorded on a Infralyum FT-2 spectrometer (nujol suspensions), the H NMR
spectra on a Bruker AC 200 instrument (200 MHz) in DMSO-d6 and CDCl3, internal standard was TMS. The
mass spectra were obtained on a Finnigan MAT INCO S50 instrument with direct insertion of samples into the
ion source (energy of ionizing electrons was 70 eV, temperature of ionization chamber was 56-180oC).
1113

TABLE 4. Mass Spectra of the Synthesized Compounds
Com-
pound
m/z (Irel, %)
1
2
2c
510 (32), 405 (15), 105 (100), 76 (35), 43 (27)
2d
2e
2h
514 (30), 409 (17), 105 (100), 101 (38), 77 (27), 59 (38) 43 (24)
588* (48), 483 (28), 105 (94), 77 (100), 60 (16), 55 (22), 43 (27)
422 (57), 317 (48), 311 (24), 295 (10), 285 (15), 111 (100), 105 (81), 76 (29), 59 (21),
43 (18), 42 (11)
2i
2j
324 (29), 281 (100), 121 (11), 105 (13), 59 (25), 43 (49)
354 (63), 312 (66), 311 (56), 298 (27), 297 (82), 279 (34), 249 (65), 175 (33),
105 (100), 77 (91), 59 (36), 43 (62), 42 (42)
3c
510 [M–H2] (1), 496 [M–16] (46), 391 [M–121] (48), 389 ([M–H2–121]), 178 (13),
105 (100), 101 (30), 77 (51), 55 (24), 43 (53), 42 (44)
3d
500 [M–16] (28), 395 [M–121] (100), 393 [M–H2–121] (20), 105 (82), 77 (38),
59 (40), 57 (17), 55 (12), 43 (41)
3e
3f
574* [M–16] (15), 469* [M–121] (33), 105 (100), 91 (46), 77 (95), 59 (41), 43 (64)
378 (5), 360 [M–H2O] (3), 267 [M–111] (100), 190 [M–111] (61), 105 (38), 95 (73),
77 (36), 51 (12), 39 (35)
3h
3i
406 [M–H2O] (27), 392 [M–CH3OH] (14), 376 [M–CH2O] (24),
281 [M–CH3OH–111] (13), 111 (100), 105 (48), 95 (10), 77 (11), 57 (19), 43 (38)
326 (0.7), 308 [M–H2O] (20), 293 [M–H2O–CH3] (40), 267 [M–59] (100),
265 [M–59–H2] (98), 251 [M–H2O–CH3NCO] (12), 105 (21), 101 (10), 80 (38),
76 (17), 59 (24), 43 (59), 42 (43)
3j
338 [M–H2O] (15), 323 [M–H2O–CH3] (45), 308 [M–H2O–CH2O] (25),
297 [M–59] (28), 281 [M–H2O–CH3NCO] (100), 265 (43), 91 (45),
77 (45), 59 (71), 43 (69)
4а
452 (7), 347 (42), 332 (19), 331 (13), 305 (13), 183 (10), 171 (14), 155 (11),
141 (12), 107 (14), 105 (100), 101 (21), 83 (13), 78 (13), 77 (74), 60 (14), 57 (36),
56 (13), 55 (25), 43 (19)
4b
4c
4d
450 [M–CH3OH] (50), 407 (13), 377 [M–105] (6), 345 [M–CH3OH–105] (13),
302 (10), 171 (5), 105 (100), 77 (34), 59 (40), 43 (35)
576 (46), 472 (100), 457 (11), 180 (16), 105 (27), 101 (34), 95 (27), 76 (15), 59 (35),
57 (16), 55 (15), 43 (41), 42 (21), 41 (20)
580 (8), 475 (100), 433 (23), 171 (17), 141 (12), 105 (97), 101 (36), 84 (20), 83 (25),
78 (10), 77 (61), 73 (13), 70 (10), 60 (12), 59 (35), 58 (14), 57 (29), 56 (25), 55 (26),
43 (43), 42 (27), 41 (18), 39 (19), 38 (14)
4e
4f
654* (8), 613* (17), 549* (56), 507* (9), 171 (5), 105 (100), 101 (11), 59 (30),
58 (30), 57 (13), 56 (16), 51 (13), 45 (15), 44 (36), 43 (51)
442 (71), 425 (11), 399 (19), 347 (86), 332 (69), 305 (22), 272 (13), 268 (13),
171 (17), 105 (13), 101 (55), 98 (31), 95 (98), 93 (15), 82 (14), 70 (15), 69 (17),
59 (100), 57 (55), 56 (36), 55 (26), 53 (15), 45 (10), 43 (88), 41 (37), 39 (47)
4g
440 [M–CH3OH] (100), 411 (41), 397 (27), 377 (12), 372 (17), 370 (12), 329 (13),
301 (14), 171 (9), 149 (11), 105 (29), 95 (86), 76 (12), 59 (50), 57 (31), 56 (17),
55 (22), 43 (57), 42 (36), 41 (18), 39 (30), 38 (21)
4h
4i
488 (0.5), 456 [M–CH3OH] (78), 413 (24), 377 (16), 345 (15), 329 (14), 301 (10),
171 (8), 111 (100), 105 (15), 82 (16), 59 (15), 39 (11)
390 (82), 374 (12), 347 (100), 332 (88), 305 (49), 303 (18), 291 (28), 289 (18),
271 (11), 265 (19), 229 (12), 184 (17), 183 (10), 178 (20), 171 (37), 165 (11),
155 (12), 141 (32), 139 (10), 127 (15), 115 (13), 105 (25), 101 (16), 76 (14), 59 (21),
53 (16), 51 (10), 44 (29), 43 (54), 42 (40), 41 (26)
5a
5b
5c
402 [M–98] (65), 372 (12), 371 (29), 370 (16), 297 (7), 265 (13), 105 (100),
95 (21), 77 (8), 76 (75), 59 (31), 57 (13), 55 (13), 53 (12), 43 (33), 42 (11), 39 (12)
496 [M–98] (44), 495 [M–99] (12), 391 [M–98–105] (22), 105 (100), 101 (15),
95 (11), 82 (16), 76 (38), 59 (24), 57 (16), 43 (35), 42 (24), 41 (18), 39 (16)
500 [M–98] (12), 499 [M–99] (22), 396 (23), 395 (21), 105 (100), 101 (35), 99 (22),
83 (21), 78 (14), 77 (75), 59 (31), 57 (27), 56 (15), 55 (27), 43 (27), 42 (20),
40 (11), 39 (14), 38 (14)
5d
392 [M–98] (20), 391 [M–99] (16), 360 [M–98–CH3OH] (100), 95 (42), 59 (13),
44 (12), 43 (16)
1114

TABLE 4 (continued
1
2
5e
7a
408 [M–98] (12), 377 [M–98–CH3O] (21), 376 [M–98–CH3OH] (36),
297 [M–98–111] (18), 265 (15), 252 (11), 181 (10), 180 (14), 179 (29), 164 (21),
113 (21), 111 (100), 101 (17), 99 (24), 91 (11), 84 (15), 83 (16), 81 (12), 77 (11),
71 (17), 59 (29), 57 (19), 56 (17), 55 (10), 53 (13), 46 (12), 45 (44), 41 (20)
348 (44), 291 (100), 151 (15), 145 (15), 128 (29), 115 (30), 101 (26), 89 (11), 76 (26),
66 (11), 59 (16), 58 (40), 57 (12), 51 (24), 45 (14), 44 (12), 43 (56), 42 (29), 41 (26)
7b
378 (100), 346 (5), 321 (98), 303 (37), 289 (66), 274 (29), 101 (44), 59 (62), 43 (72)
_______
*Peaks are given for the light 79Br isotope.
A check on the progress of reactions and the homogeneity of substances was carried out by TLC on
Sorbfil plates, eluent was methylene chloride–acetone–petroleum ether, 4.5:7:14. Visualization was with iodine
or bromine vapor.
N-(2-Benzoyl-4,6-disubstituted[2,3-b]pyrid-3-yl)amides 2a,b,f,g were synthesized as described
previously in [15].
N-(2-Benzoyl-4,6-diphenylthieno[2,3-b]pyrid-3-yl)benzamide (2c). Benzoyl chloride (1.2 g, 8.8 mmol)
was added to a hot solution of amine 1c (3 g, 7.4 mmol) in chlorobenzene (50 ml). The reaction mixture was
boiled for 16 h. The crystals precipitated on cooling were filtered off, dried, and recrystallized from ethanol.
Colorless crystals of compound 2c (3.2 g) were obtained.
Compounds 2d,e were obtained analogously from amines 1d,e, thenoyl-substituted 2h from amine 1h
and thiophene-2-carboxylic acid chloride, and compounds 2i,j from amines 1ij and acetyl chloride in dioxane.
N-{2-[Hydroxy(phenyl)methyl]-4,6-disubstituted[2,3-b]pyrid-3-yl}amides 3a,b,g were obtained by
the reduction of ketones 2a,b,g with NaBH4 by the procedure of [15].
N-{2-[Hydroxy(phenyl)methyl]-4,6-diphenylthieno[2,3-b]pyrid-3-yl}benzamide (3c). Compound 2c
(2.7 g, 5.3 mmol) was dissolved in ethanol (50 ml) by heating with constant stirring. NaBH4 (0.24 g, 6.4 mmol)
was added in portions to the obtained solution. The reaction mixture was maintained at 60-70oC for 3 h, then
cooled, and poured into H2O (250-300 ml) with vigorous stirring. The precipitated crystals were filtered off,
dried, and recrystallized from ethanol. Compound 3c (2.4 g) was obtained as colorless crystals.
Compounds 3d-f,h-j were obtained analogously from the appropriate acyl derivatives 2d-f,h-j.
N-{2-[(5-Methyl-2-furyl)(phenyl)methyl]-4,6-dimethylthieno[2,3-b]pyrid-3-yl}benzamide
(4a).
Catalyst (0.3 ml), prepared from 70% perchloric acid (2 ml, 3.3 mmol), acetic anhydride (5.3 ml, 5.6 mmol), and
acetic acid (3 ml, 5.2 mmol), was added to a solution of alcohol 3a (0.2 g, 5 mmol) and α-methylfuran (0.67 ml,
7.5 mmol) in dioxane (20 ml). The mixture obtained was boiled for 4 h until complete consumption of the initial
alcohol (check by TLC), then the mixture was poured into water (100 ml), and neutralized with dry NaHCO3 to
pH ≈ 7. The precipitated crystalline solid was filtered off, dried, and recrystallized with silica gel from an ethyl
acetate–petroleum ether, 2:1 mixture. Compound 3a (0.18 g) was obtained as colorless crystals.
Compounds 4b-i were obtained analogously from alcohols 3b-i.
N-[2-(2,5-Dioxo-1-phenylhexyl)-4,6-diphenylthieno[2,3-b]pyrid-3-yl]benzamide (5b). Concentrated
HCl (1 ml) was added to a solution of compound 4c (1.0 g, 1.7 mmol) in glacial acetic acid (20 ml) and the
mixture boiled for 3 h. After the equilibrium 4c ↔ 5b had been established (check by TLC) the reaction mixture
was poured into water (50 ml), and neutralized with dry NaHCO3 to pH ≈ 7. The precipitated crystalline solid
1
was filtered off and dried. A mixture (0.96 g) of compounds 4c and 5b (according to H NMR data) was
obtained. Product 5b (0.32 g) was isolated as colorless crystals by chromatography on a column (2×20 cm, silica
gel 40-100 mesh, eluent acetone–petroleum ether–methylene chloride, 7:28:4.5).
Compounds 5a,c-e were obtained analogously from amides 4b,d,g,h.
1115

4-(6,8-Dimethyl-3-phenyl-1H-pyrrolo[2',3':4,5]thieno[2,3-b]pyrid-2-yl)butan-2-one (7a). A.
A
solution of compound 4i (0.5 g, 1.28 mmol) in acetic acid (10 ml) and HCl (0.5 ml) was maintained at 40-50oC
for 18 h (check by TLC). The reaction mass was poured into water (100 ml) and neutralized with dry NaHCO3
to pH ≈ 7. The precipitated crystalline solid was filtered off, dried, and recrystallized from alcohol with the
addition of activated carbon. Compound 7a (0.2 g, 45%) was obtained as colorless crystals.
B. A solution of compound 4i (0.7 g, 1.8 mmol) in ethyl alcohol (20 ml) saturated with dry HCl was
boiled for 5 h (check by TLC), then poured into water (70 ml), and neutralized with dry NaHCO3 to pH ≈ 7. The
precipitated crystalline solid was filtered off, dried, and recrystallized from chloroform with addition of silica
gel. Compound 7a (0.42 g, 67%) was obtained as pale-yellow crystals.
4-(8-Methoxymethyl-6-methyl-3-phenyl-1H-pyrrolo[2',3':4,5]thieno[2,3-b]pyrid-2-yl)butan-2-one
(7b). A solution of alcohol 3j (0.8 g, 2.2 mmol), α-methylfuran (0.3 ml, 3.4 mmol), catalyst (see synthesis of
compound 4a) (0.3 ml) in dioxane (30 ml) was boiled for 5 h until disappearance of the initial alcohol. The
reaction mass was poured into water (100 ml), and neutralized with dry NaHCO3. The precipitated solid, a
mixture of methane 4j and indolothienopyridine 7b, was dissolved in alcohol (20 ml), the solution was saturated
with dry HCl, and boiled for 12 h until disappearance of methane 4j. After cooling, the solution was poured into
water (100 ml), and neutralized with dry NaHCO3. The precipitated solid was filtered off, recrystallized from
ethanol, and the target product 7b (0.33 g) was obtained as pale-yellow crystals.
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