Isovaleric aldehyde in the synthesis of 4-isobutyl-substituted pyridine-2(1H)-thiones, 4H-pyrans, and 1,3-cyclohexadiene

Article abstract of DOI:10.1007/s11176-005-0247-5

Cyclocondensation of isovaleric aldehyde with various CH acids [benzoylacetonitrile, malononitrile, cyanothioacetamide, 4-hydroxycoumarin, resorcinol, 3-phenylpyrazol-5(1H)-one, 3-morpholinocrotonanilide] in the presence of amines yields isobutyl-substituted 4H-pyrans, 1,3-cyclohexadiene, and pyridine-2(1H)-thiones. The latter compounds were used in the synthesis of substituted 2-pyridino thioethers and thieno[2,3-b]pyridine. 2005 Pleiades Publishing, Inc.

Full text of DOI:10.1007/s11176-005-0247-5

Russian Journal of General Chemistry, Vol. 75, No. 3, 2005, pp. 440 446. Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 3, 2005,
pp. 476 482.
Original Russian Text Copyright
2005 by Dyachenko.
Isovaleric Aldehyde in the Synthesis of 4-Isobutyl-Substituted
Pyridine-2(1H)-thiones, 4H-Pyrans, and 1,3-Cyclohexadiene
V. D. Dyachenko
Shevchenko National Pedagogical University, Lugansk, Ukraine
Received July 24, 2003
Abstract Cyclocondensation of isovaleric aldehyde with various CH acids [benzoylacetonitrile, malono-
nitrile, cyanothioacetamide, 4-hydroxycoumarin, resorcinol, 3-phenylpyrazol-5(1H)-one, 3-morpholinocroton-
anilide] in the presence of amines yields isobutyl-substituted 4H-pyrans, 1,3-cyclohexadiene, and pyridine-
2(1H)-thiones. The latter compounds were used in the synthesis of substituted 2-pyridino thioethers and thi-
eno[2,3-b]pyridine.
Among alkyl-substituted pyridines there are central
nervous system activators [1], fungicides, and agents
for treating hyperlipoproteinemia [3], brain edema,
asthma, shock, and other human diseases [4]. At the
same time, alkyl-substituted pyridinechalcogenones
and pyrans, which are also potentially bioactive [5, 6],
are studied poorly [7].
lide III in ethanol at 20 C in the presence of morpho-
line yields N-phenyl-4-isobutyl-6-methyl-2-thioxo-3-
cyano-1,2-dihydropyridine-5-carboxamide VII. The
reaction pathway apparently involves formation of
alkene IV by the Knoevenagel reaction [11]. This is
followed by alkylation of enamine III with olefin IV,
which can be considered as Stork reaction [11]. The
resulting adduct V undergoes intramolecular cyclo-
condensation to form substituted morpholinium 1,4-
dihydropyridine-2-thiolate VI, transforming into pyri-
dinethione VII on treatment with HCl.
Studies of the synthesis of alkyl-substituted hetero-
cycles from aliphatic aldehydes and CH acids [8 10]
showed that condensation of isovaleric aldehyde I
with cyanoacetamide II and 3-morpholinocrotonani-
Me
Me
O
O
Me
Me
PhHN
CN
NH
CN
O
PhHN
Me
III
Me
CN
Me
+
+
Me
N
O
H2N
S
CHO
H2N
S
N
O
H2N
S
I
II
III
IV
V
Me
Me
Me
Me
O
O
CN
CN
H+
2[H]
PhHN
Me
PhHN
Me
N
H
S
S
N
+
H
NH2
O
VI
VII
1070-3632/05/7503-0440 2005 Pleiades Publishing, Inc.

ISOVALERIC ALDEHYDE IN THE SYNTHESIS
441
Table 1. Constants, yields, and elemental analyses of substituted pyridinethiones VII and XI, 2-pyridino thioethers XIIIa
and XIIIb, thieno[2,3-b]pyridine XIV, pyrans XXI, XXVII, and XXVIII, 1,3-cyclohexadiene XXXI, and pentanodinitrile
XXXIV
Found, %
H
Calculated, %
H
mp,
(solvent for)
crystallization)
C
Formula
C
N
C
N
VII
XI
XIIIa
XIIIb
XIV
82
66
93
74
80
76
85
90
77
67
243 245(AcOH)
220 222(AcOH)
168 169(i-PrOH)
109 111(MeOH)
263 265(AcOH)
262 264(EtOH)
186 188a (EtOH)
131 132(EtOH)
141 143(EtOH)
143 145(i-PrOH)
66.50
69.71
67.15
65.69
67.28
61.95
68.70
69.70
71.50
60.51
5.74
5.02
4.48
5.08
4.30
5.92
6.52
6.85
7.48
7.42
13.08
14.10
9.60
11.37
9.56
16.88
11.56
8.41
21.02
14.96
C18H19N3OS
C17H15N3S
66.43
69.60
67.33
65.73
67.33
62.17
68.83
69.92
71.61
60.62
5.88
5.15
4.52
5.24
4.52
6.14
6.60
6.79
7.51
7.50
12.91
14.32
9.42
11.50
9.42
17.06
11.47
8.58
20.88
14.88
C25H20ClN3OS
C20H19N3O2S
C25H20ClN3OS
C17H20N4OS
C14H16N2O2
C19H22N2O3
C16H20N4
XXI
XXVII
XXVIII
XXXI
XXXIV
C19H28N4O4
a
Sublimes at 150 C.
With benzoylacetonitrile VIII used in the above
reaction instead of enamine III, 4-isobutyl-2-thioxo-6-
phenyl-1,2-dihydropyridine-3,5-dicarbonitrile XI was
obtained. Its 4-aryl-substituted isostructural analog
was prepared previously by the reaction of arylmethyl-
enebenzoylacetonitrile with cyanothioacetamide [12].
pyridine-2-thiolate X. The latter product under the
reaction conditions is protonated and oxidized (appar-
ently, with atmospheric oxygen) to pyridinethione XI.
The structures of VII and XI were confirmed both
by physicochemical and spectral data (Tables 1, 2)
and by chemical transformations. In particular, the
reactions of thione XI with compounds XII in basic
media yield organic sulfides XIII. Treatment of XIIIa
with an alkali yielded substituted thieno[2,3-b]pyri-
dine XIV, which confirms the structure of thione XI
and thioether XIIIa [13].
The probable scheme of formation of XI is shown
below. CH Acid VIII adds by the Michael reaction
[11] to Knoevenagel reaction product IV; the resulting
adduct IX undergoes regioselective cyclocondensation
into substituted N-methylmorpholinium 1,4-dihydro-
Me
Me
Me
Me
CN
NC
Ph
NMe
I, II, O
CN
NC
Me
NC
Ph
S
N
H
IV
H2O
O
H2N
S
O
H2O
+
NHMe
O
VI
IX
Me
Me
Me
Cl
Me
Me
Me
CN
NH2
Z/KOH
XIIIa, XIIIc
Hlg
CN
NC
Ph
NC
Ph
H+
NC
Ph
KOH
DMF
2[H]
O
DMF
N
H
S
S
Z
N
H
N
S
XI
XIIIa, XIIIb
XIV
XII, Hlg = Br (a), Cl (b); XII, XIII, Z = 4-ClC6H4CO (a), COOMe (b).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 3 2005

442
DYACHENKO
1
Table 2. IR and H NMR data for substituted pyridinethiones VII and XI, 2-pyridino thioethers XIIIa and XIIIb, thieno-
[2,3-b]pyridine XIV, pyrans XXI, XXVII, and XXVIII, 1,3-cyclohexadiene XXXI, and pentanodinitrile XXXIV
1
IR spectrum, , cm
1H NMR spectrum, , ppm (J, Hz)
Comp.
no.
CH(Me)2, CH(Me)2,
(C N)
(NH2), (NH2), (C=O)
3300, 1666
CH2
other signals
d
m
VIIa
XIa
2230
0.89
(J 8.40)
1.04
(J 8.48)
1.00
2.00
2.12
2.10
2.60 d 2.41 s (3H, C6Me), 7.13 7.63 m
(J 7.95) (5H, Ph), 10.48 br.s (1H, NHCO)
2.73 d 7.51 7.73 m (5H, Ph)
(J 8.14)
2.87 d 5.01 s (2H, SCH2), 7.30 d and
(J 8.05) 8.03 d (2H each, C6H4, J 8.3), 7.41
7.69 m (5H, Ph)
2232 sh
XIIIa
2228 sh 1712
(J 8.39)
XIIIb
XIV
2227
2225
1740
1.02
(J 8.20)
2.13
2.09
1.24
1.65
2.84 d 3.60 s (3H, MeO), 4.25 s (2H,
(J 8.11) SCH2), 7.69 m (3H, Ph), 7.88 m
(2H, Ph)
2.79 d 7.48 d and 8.15 d (2H each, C6H4, J
(J 8.10) 8.0), 7.60 7.92 m (5H, Ph),
3214, 3352, 3418, 1670,
1738
1.14
(J 8.18)
8.17 br.s (2H, NH2)
XXI
3214, 3300, 3452, 1647
3150, 3196, 3335, 1644
0.68
(J 8.27)
1.93 m 3.84 t (1H, C4H, J 9.15), 7.02
7.66 m (9H, NH2, CSNH2, Ph),
11.82 br.s (1H, N2H)
XXVII 2200
XXVIII 2199
0.89
(J 8.30)
1.34 m 3.36 d (1H, C4H, J 6.20), 6.34 s
(1H, C8H), 6.07 d (1H, C5H, J 9.10),
6.68 br.s (2H, NH2), 6.94 d (1H,
C6H), 9.55 br.s (1H, OH)
3211, 3332, 3420, 1648,
1688
0.95 mb
1.90
1.58
1.76
1.47 d.d 0.95 m (2H, CH2CH3),b 3.30 t (1H,
(J 7.12) C4H, J 5.64), 3.94 q (2H, OCH2, J
7.10), 6.54 br.s (2H, NH2), 7.38 br.s
(5H, Ph)
XXXI
2210,
2254
3212,
1676
3450,
1650
0.95 d
(J 8.14)
1.40 m 1.14 d [6H, (CH3)2, J 8.15], 2.19 m
[1H, CH(Me)2], 3.10 t (1H, C5H, J
7.12), 5.22 s (1H, C3H), 7.46 br.s
(2H, NH2)
1.54 m 3.20 3.78 m [16H, (C4H8NO)2],
4.29 d and 4.38 d [1H each,
(CHCN)2], 4.50 m (1H, CH)
XXXIV 2249
0.91 d,
0.98 d
(J 8.33)
a
6
b
The N H proton signal is not observed, probably besause of deuterium exchange.
The signals overlap.
The three-component condensation of isovaleric
in the presence of amines, adducts of type XVII can
aldehyde I, cyanothioacetamide II, and 4-hydroxy-
coumarin XV in ethanol at 20 C in the presence of
morpholine yields 2-amino-4-isobutyl-5-oxo-4H,5H-
pyrano[3,2-c]chromene-3-carbonitrile XX (method a).
With 3-phenylpyrazol-5(1H)-one XVI used as the
third component instead of XV, 6-amino-4-isobutyl-
3-phenyl-2H,4H-pyrano[2,3-c]pyrazole-5-carbothiox-
amide XXI is obtained. It is reasonable to assume the
formation of the corresponding Michael adducts XVII
and XVIII in the course of these reactions. It is known
that, in three-component condensation of aromatic al-
dehydes, cyanothioacetamide, and 4-hydroxycoumarin
be isolated and characterized as ammonium salts [14].
The structures of XX and XXI were confirmed by
1
IR, H NMR, and mass spectra (Table 2), and also by
independent synthesis from isovaleric aldehyde I,
malononitrile XIX, and 4-hydroxycoumarin XV
(method b) [15].
The condensation of isovaleric aldehyde I with
malononitrile XIX and resorcinol XXII in ethanol in
the presence of N-methylmorpholine yields 2-amino-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 3 2005

ISOVALERIC ALDEHYDE IN THE SYNTHESIS
443
7-hydroxy-4-isobutyl-4H-chromene-3-carbonitrile
XXVII. Its isostructural analogs can be used for pro-
tection of agricultural plants from the damage caused
by herbicides [16] and as antiasthmatic agents [17].
With ethyl 3-oxo-3-phenylpropanoate XXIII used
instead of resorcinol XXII in this reaction, ethyl
6-amino-4-isobutyl-2-phenyl-5-cyano-4H-pyran-3-car-
boxylate XXVIII is obtained.
Ph
OH
Me
O
O
,
Me
N
Me
C(S)NH2
O
,
N
Me
N
H
O
XV
O
N
H
Ph
N
O
H
XVI
CN
O
C
I + II
OH
N
H
a
OH
N<
NH2
S
XVIII
Me
XVII
Me
H2S
NMe
Me
O
CN
CN
,O
CN
XIX
O
Me
NH2
Ph
C(S)NH2
NH2
O
I + XV
b
HN
XX
O
XXI
N
Me
O
O
O
NMe
OH,
O
NMe
Me
Me
OEt,
Ph
XXIII
HO
Me
CN
XXII
H2O
EtOOC
Ph
C(S)NH2
I + XIX
H2O
C
N<
OH
CN
XXIV
XXVI
Me
Me
Me
Me
CN
Me
CN
Me
EtOOC
Ph
CN
C
N<
NH2
O
OH
XXV
HO
HO
NH2
O
XXVII
XXVIII
Compounds XXVII and XXVIII are apparently
formed via intermediate isopentylidenemalononitrile
XXIV to which CH acids XXII and XXIII add by the
Michael reaction. The corresponding adducts XXV
and XXVI undergo intramolecular cyclization to give,
respectively, XXVII and XXVIII. This reaction path-
way is confirmed by two-component cyclization of
isovaleric aldehyde I with malononitrile XIX. This
reaction yielded 1-amino-5-isobutyl-4-isopropyl-1,3-
cyclohexadiene-2,6,6-tricarbonitrile XXXI as a result
of Michael dimerization of alkene XXIV into adduct
XXIX followed by the Thorpe Ziegler [18] transfor-
mation into imine XXX. The latter is stabilized in the
form of substituted 1,3-cyclohexadiene XXXI.
The structure of XXXI is confirmed by the spectral
data (Table 2). Its mass spectrum contains a molecular
peak at m/z 268, in accordance with the nitrogen
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 3 2005

444
DYACHENKO
Me
Me
Me
Me
O
NMe
Me
CN
Me
CN
Me
Me
Me
I + XIX
XXIV
Me
Me
CN
Me
CN
NH
CN
H2O
C N CN
NH2
^
CN
XXX
CN
XXXI
CN
XXIX
rule [19]. The high intensity of the [M]+ peak (see
Experimental) at the ionizing electron energy of 70 eV
is typical of compounds with the high formal degree
of unsaturation [20].
characteristic signals of the protons of aliphatic sub-
stituents and C5H proton (Table 2).
The two-component condensation of isovaleric
aldehyde I with 3-morpholino-3-oxopropanonitrile
XXXII in the presence of morpholine follows the
Knoevenagel reaction pattern and yields alkene
XXXIII. However, we failed to isolate it because of
easy subsequent Michael addition of CH acid XXXII
to XXXIII under the reaction conditions. Adduct
XXXIV formed in the process is stable; it was iso-
lated and characterized (Tables 1, 2).
The IR spectrum contains stretching vibration
1
bands of a conjugated nitrile group at 2210 cm and
1
a nonconjugated nitrile group at 2254 cm , and also
1
1
stretching (3212, 3450 cm ) and bending (1650 cm )
1
vibration bands of the amino group. The H NMR
spectrum of XXXI contains characteristic signal of
amino group protons as a broadened singlet at
7.46 ppm, a C3H proton singlet at 5.22 ppm, and
Me
Me
Me
NH
O
CN
N
Me
CN
XXXII
I +
NC
N
CN
N
O
O
N
O
O
O
O
O
O
XXXII
XXXIII
XXXIV
The yield of XXXIV is the highest at I : XXXII =
1 : 2, which confirms the suggested reaction mechan-
ism. Similar adducts were obtained previously by con-
densation of aliphatic aldehydes with cyanoacetamide
[21]. At the same time, sulfur analogs of adducts
XXXIV cannot be prepared because of their easy
transformation into 5-amino-8-isobutyl-7-isopropyl-6-
thiocarbamoyl-4-cyano-2-azabicyclo[2.2.2]oct-5-ene-
3-thione [9, 22].
(300.13 MHz, compounds XI, XXXIV), and Bruker
DR-500 (500.13 MHz, compound XIIIb) spectrom-
eters (solutions in DMSO-d6, internal reference TMS).
The mass spectra were recorded on a Kratos MS-890
spectrometer (70 eV). The melting points were deter-
mined with a Koefler unit. The reaction progress was
monitored by TLC (Silufol UV-254, acetone hexane,
3 : 5, development with iodine vapor).
N-Phenyl-4-isobutyl-6-methyl-2-thioxo-3-cyano-
1,2-dihydropyridine-5-carboxamide VII. A drop of
morpholine was added to a mixture of 1.08 ml of iso-
valeric aldehyde I and 1.0 g (10 mmol) of cyanothio-
acetamide II in 15 ml of ethanol at 20 C. The mixture
was stirred for 10 min. Then 2.46 g of enamine III
EXPERIMENTAL
The IR spectra were taken on an IKS-29 spectrom-
1
eter (mulls in mineral oil). The H NMR spectra were
taken on Bruker WP-100SY (100 MHz, compounds
VII, XIIIa, XXVII), Gemini-200 (199.975 MHz, com- was added, and the mixture was stirred for 30 min and
pounds XX, XXVIII), Bruker WM-250 (250.13 MHz,
compounds XIV, XXI, XXXI), Bruker AM-300
allowed to stand at room temperature for 24 h. After
that, the mixture was diluted with 10% HCl to pH 5
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ISOVALERIC ALDEHYDE IN THE SYNTHESIS
445
and allowed to stand for 48 h. The precipitate of pyri-
dinethione VII (Tables 1, 2) was filtered off and
washed with water, ethanol, and hexane.
to XX (method a) using XVI instead of XV. The
characteristics of XXI are given in Tables 1 and 2.
Mass spectrum, m/z (Irel, %): 330 (7) [M + 2]+, 328
(9) [M]+, 326 (10) [M 2]+, 253 (64), 229 (21), 228
(79), 214 (20), 213 (82), 186 (15), 185 (24), 173 (85),
161 (26), 160 (100), 144 (20), 129 (28), 115 (27), 104
(30), 103 (87), 91 (14), 77 (85), 58 (92).
4-Isobutyl-2-thioxo-6-phenyl-1,2-dihydropyridi-
ne-3,5-dicarbonitrile
XI.
N-Methylmorpholine
(1.1 ml) was added to a suspension of 1.0 g of cyano-
thioacetamide II in 15 ml of ethanol at 20 C. The
mixture was stirred for 8 min until a homogeneous
solution formed. Then 1.08 ml of isovaleric aldehyde
I was added, and the mixture was stirred for 10 min.
After that, 1.45 g of VIII was added, and the mixture
was stirred for an additional 30 min. After standing
for a day, the mixture was diluted with 10% HCl and
left for 48 h at room temperature. The precipitate of
pyridinethione XI (Tables 1, 2) was separated and
washed with water, ethanol, and hexane. Mass spec-
trum, m/z (Irel, %): 295 (2) [M + 2]+, 294 (11) [M +
1]+, 293 (40) [M]+, 292 (63) [M 1]+, 279 (7), 278
(25), 253 (6), 252 (17), 251 (100), 250 (15), 224 (7),
207 (9), 77 (13).
2-Amino-7-hydroxy-4-isobutyl-4H-chromene-3-
carbonitrile XXVII. To a solution of 1.08 ml of iso-
valeric aldehyde I in 15 ml of ethanol, we added
0.66 g of malononitrile XIX and three drops of
N-methylmorpholine; the mixture was stirred for
10 min. Then 1.10 g of resorcinol XXII was added,
and the mixture was stirred for 30 min and left at
room temperature. In 3 days, colorless crystals of
XXVII (Tables 1, 2) formed, which were filtered off
and washed with ethanol and hexane.
Ethyl 6-amino-4-isobutyl-2-phenyl-5-cyano-4H-
pyran-3-carboxylate XXVIII was prepared similarly
to XXVII, with ethyl 3-oxo-3-phenylpropanoate
XXIII used instead of resorcinol XXII. The charac-
teristics of XXVIII are given in Tables 1 and 2. Mass
spectrum, m/z (Irel, %): 326 (4) [M]+, 271 (18), 269
(100), 241 (18), 197 (5), 105 (27), 77 (14), 41 (6).
4-Isobutyl-6-phenyl-2-(Z-methylsulfanyl)pyridi-
ne-3,5-dicarbonitriles XIIIa and XIIIb. To a solu-
tion of 2.93 g of pyridinethione XI in 8 ml of DMF,
we added successively 5.6 ml of 10% aqueous KOH
and 100 ml of appropriate halide XII. The mixture
was stirred for 30 min and diluted with an equal
volume of water. The precipitate of XIIIa or XIIIb
(Tables 1, 2) was separated and washed with water,
ethanol, and hexane.
1-Amino-5-isobutyl-4-isopropyl-1,3-cyclohexadi-
ene-2,6,6-tricarbonitrile XXXI. A mixture of 1.08 ml
of isovaleric aldehyde I, 0.66 g of malononitrile XIX,
and three drops of N-methylmorpholine in 15 ml of
ethanol was stirred for 1 h and allowed to stand for
a day. A colorless crystalline precipitate of XXXI
(Tables 1, 2) formed, which was separated and washed
with ethanol and hexane. Mass spectrum, m/z (Irel,
%): 270 (8) [M + 2]+, 269 (22) [M + 1]+, 268 (87)
[M]+, 254 (10), 253 (25), 226 (25), 225 (76), 212
(28), 211 (95), 198 (28), 197 (95), 186 (30), 184 (69),
171 (30), 170 (96), 169 (100), 156 (60), 145 (28), 144
(96), 119 (20), 109 (18), 79 (8), 69 (17).
3-Amino-4-isopropyl-6-phenyl-2-(4-chlorophe-
nylbenzoyl)thieno[2,3-b]pyridine-5-carbonitrile
XIV. To a solution of 4.46 g of XIIIa in 15 ml of
DMF, we added with stirring 5.6 ml of 10% aqueous
KOH. The mixture was stirred for 1 h and then grad-
ually diluted with an equal volume of water. The
precipitate of XIV (Tables 1, 2) was filtered off and
washed with water, ethanol, and hexane.
2-Amino-4-isobutyl-5-oxo-4H,5H-pyrano[3,2-c]-
chromene-3-carbonitrile XX. a. A 0.87-ml portion
of morpholine was added with stirring at 20 C to a
mixture of 1.08 ml of isovaleric aldehyde I and 1.0 g
of cyanothioacetamide II in 15 ml of ethanol. The
mixture was stirred for 5 min, after which 1.62 g of
4-hydroxycoumarin was added, and the mixture was
stirred for 15 min and allowed to stand for a day. The
finely crystalline colorless precipitate of XX was
filtered off and washed with ethanol and hexane.
Yield 74%. As judged from the melting point, chro-
3-Isobutyl-2,4-di(morpholinocarbonyl)pentano-
dinitrile XXXIV. A mixture of 1.08 ml of isovaleric
aldehyde I, 3.08 g of 3-morpholino-3-oxopropano-
nitrile XXXII, and three drops of morpholine in 15 ml
of ethanol was stirred for 25 min at room temperature
to obtain a homogeneous solution. The mixture was
allowed to stand at room temperature for 48 h. The
precipitate was filtered off and washed with ethanol
and hexane. Compound XXXIV (Tables 1, 2) was
thus obtained as a colorless powder. Mass spectrum,
m/z (Irel, %): 376 (14) [M]+, 308 (10), 290 (43), 223
(100), 154 (19), 114 (25), 86 (27), 70 (51), 56 (78),
41 (63).
1
matographic data, and H NMR and IR spectra, the
product is identical to that obtained by method b [15].
6-Amino-4-isobutyl-2H,4H-pyrano[2,3-c]pyra-
zole-5-carbothioxamide XXI was prepared similarly
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446
DYACHENKO
pounds: Coll. of Scientific Papers), Saratov, 2000,
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