Synthesis of derivatives of the new condensed system 4H,7H-furo[3′, 4′:6,7]cyclohepta[1,2-b]pyran

Article abstract of DOI:10.1007/s10593-008-0037-1

8-Hydroxy-1,3-dimethyl-4H-cyclohepta[c]furan-4-one reacts with arylidenemalononitriles and, like 1,3-oxo enols, forms the corresponding condensed 2-amino-4H-pyrans. The analogous reaction with 3-(dicyanomethylene) indolin-2-ones give spirocyclic 2-amino-4

Full text of DOI:10.1007/s10593-008-0037-1

Chemistry of Heterocyclic Compounds, Vol. 44, No. 2, 2008
SYNTHESIS OF DERIVATIVES
OF THE NEW CONDENSED SYSTEM
4H,7H-FURO[3′,4′:6,7]CYCLOHEPTA-
[1,2-b]PYRAN
M. Yu. Arsen'eva and V. G. Arsen'ev
8-Hydroxy-1,3-dimethyl-4H-cyclohepta[c]furan-4-one reacts with arylidenemalononitriles and, like 1,3-
oxo enols, forms the corresponding condensed 2-amino-4H-pyrans. The analogous reaction with
3-(dicyanomethylene)indolin-2-ones give spirocyclic 2-amino-4H-pyrans. The 4-aminopyrimidine ring is
formed on the basis of the enamino nitrile fragment of the new pyrans by successive reaction with
triethoxymethane and then with aqueous ammonia.
Keywords: 2-amino-4H-pyran, 4-aminopyrimidine, benzylidene malononitrile, hydroxytropone, enol,
pyrano[2,3-d]pyrimidine, tropolone, tropone, Michael addition.
2-Amino-4H-pyrans have attracted the attention of researchers for more than a decade [1-4]. This interest
is explained by the prospects of using them as drugs for the treatment of diseases of the central nervous system
(dementia, Parkinson’s disease) [5], arthritis, sclerosis, tumors [6], and arterial hypertension [7]. They are also
attracted by the comparative simplicity of their synthesis and the possibility of using them as synthons for the
production of more complicated condensed systems [8-10].
The aim of the present investigation was to synthesize condensed 2-amino-3-cyano-4H-pyrans from
8-hydroxy-1,3-dimethylcyclohepta[c]furan-4-one (1) and certain ylidene derivatives of malononitrile.
It had been shown by numerous investigations that ylidene malononitriles form 2-amino-3-cyano-
4H-pyrans in reaction with active enols having various structures – electron-rich phenols, naphthols, carbocyclic
and heterocyclic 1,3-oxo enols [1-4].
Compound 1, which became available comparatively recently, is also a typical enol (or, more accurately,
1
a vinylog of a cyclic 1,3-oxo enol – 1,5-oxo dienol). This is demonstrated by its IR and H NMR spectra and
also by its physical characteristics – it is a yellow substance with a comparatively high melting point and low
solubility in nonpolar or low-polarity solvents [11].
Earlier neither the hydroxytropone 1 itself nor its benzannulated analogs had been brought into similar
reactions with unsaturated nitriles. These reactions had also not been investigated for monocyclic hydroxytropones.
Their study is therefore of interest, while the expected products containing the 4H-pyran fragment, which has already
exhibited its medicinal activity, and the heteroannulated tropone cyclic system, which also exhibits various types of
activity in the composition of natural and synthetic compounds [12], may have useful physiological activity.
__________________________________________________________________________________________
Southern Federal University, Rostov-on-Don 344006, Russia; e-mail: arsenev.vg@gmail.com. Translated
from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 188-195, February, 2008. Original article submitted
February 14, 2007.
136
0009-3122/08/4402-0136©2008 Springer Science+Business Media, Inc.

Ar
O
CN
Ar
CN
CN
O
O
Et3N
OH
NH2
+
MeCN, 60°C
Me
Me
O
O
Me
Me
2a-k
1
2 a Ar = 4-MeOC6H4, b Ar = 4-EtOC6H4, c Ar = 4-MeSC6H4, d Ar = 4-FC6H4,
e Ar = 4-BrC6H4, f Ar = 2-FC6H4, g Ar = 2-ClC6H4, h Ar = 3,4-OCH2OC6H3,
i Ar = 2,4-Cl2C6H3, j Ar = Ph, k Ar = 2-thienyl
It was found that the hydroxytropone 1 reacts readily with arylidene derivatives of malononitrile with the
formation of the expected 2-amino-4H-pyrans 2a-k. The reaction takes place under mild conditions in
acetonitrile at 50-60°C after the addition of catalytic amounts of piperidine or triethylamine and gives yields of
30-80%.
Since the result of the reaction corresponded to the expected result, the mechanism proposed earlier for
similar reactions can be used for its description. Electrophilic attack is probably directed at position 7 of the
initial hydroxytropone, after which the Michael-type adduct undergoes intramolecular cyclization, forming
compound 2.
TABLE 1. The Characteristics of the Synthesized Compounds
Found, %
——————
Calculated, %
Com-
pound
Empirical
formula
mp, °С
Yield, %
С
Н
N
2a
2b
2c
2d
2e
2f
2g
2h
2i
C22H18N2O4
C23H20N2O4
C22H18N2O3S
C21H15FN2O3
C21H15BrN2O3
C21H15FN2O3
C21H15ClN2O3
C22H16N2O5
C21H14Cl2N2O3
C21H16N2O3
C19H14N2O3S
C22H15N3O4
C23H17N3O4
C24H19N3O4
C25H22N2O5
C23H19N3O4
70.81
70.58
71.41
71.12
67.51
67.67
69.56
69.61
59.12
59.59
69.82
69.61
66.59
66.58
67.75
68.04
61.10
61.03
73.22
73.24
65.19
65.13
68.61
68.57
69.03
69.17
69.70
69.72
69.38
69.76
69.02
68.82
4.67
4.85
4.97
5.19
4.67
4.65
4.27
4.17
3.73
3.57
4.11
4.17
3.91
3.99
4.27
4.15
3.35
3.41
4.69
4.68
3.77
4.03
3.99
3.92
4.39
4.29
4.69
4.63
5.09
5.15
4.75
4.77
7.55
7.48
7.30
7.21
7.01
7.17
7.72
7.73
6.42
6.62
7.67
7.73
7.31
7.40
7.21
7.21
6.73
6.78
8.43
8.13
8.29
7.99
10.77
10.90
10.71
10.52
10.46
10.16
6.65
6.51
10.68
10.47
246-248
82
44
57
42
45
53
52
63
59
32
54
75
28
56
53
46
274-276
259-261
230-232
280-282
256-258
277-279
277-279 (dec.)
252-254
2j
2k
4a
4b
4c
5
260-262
272-273
>350 (dec.)
336-337 (dec.)
265-267
160-162
7
244-246
137

The pyran 2a was synthesized successfully by a three-component condensation, when the
hydroxytropone 1, 4-methoxybenzaldehyde, and malononitrile were brought into reaction in equimolar amounts.
In this case, however, a less pure product was obtained, and after repeated recrystallization the total yield was
lower than with the use of the previously prepared ylidene derivative.
Compounds 2a-k are yellow crystalline substances poorly soluble in chloroform and alcohol and readily
soluble in pyridine and DMF.
1
The H NMR spectra of the products 2a-k contain signals for the methyl groups of the furan ring in the
form of three-protons singlets at 2.50-2.75 and 2.68-2.75 ppm, two doublets for the methine protons of the
seven-membered ring at 6.05-6.20 and 6.20-6.65 ppm, and a signal for the pyran proton in the region of
1
4.20-4.90 ppm. The broad singlet for the protons of the amino group in the H NMR spectra of the compounds,
recorded in DMSO-d6, appears in the region of 7.00-7.15 ppm, and those in the spectra obtained in CDCl3 appear
in the region of 4.50-4.60 ppm.
The IR spectra of compounds 2a-k contain absorption bands corresponding to the vibrations of the N–H
bonds of the amino groups at 3153 cm-1, the nitrile group at 2180-2193 cm-1, and the conjugated carbonyl at
1666-1693 cm-1.
In order to synthesize spiroannulated 4H-pyrans the initial hydroxytropone 1 was brought into reaction
with a series of ylidene derivatives of malononitrile obtained from such cyclic ketones as isatin, N-alkylisatins,
ninhydrin, and cyclohexanone.
The reactions with isatin derivatives 3a-c were successful. The reaction takes place under the same
conditions as the reaction of hydroxytropone 1 with arylidene malononitriles. The spiro compounds 4a-c are
formed in good yields.
1
The H NMR spectra of the products 4a-c contain signals for the methyl groups of the furan ring in the
form of three-proton singlets at 2.60 and 2.73 ppm, two doublets for the methine protons of the seven-membered
ring at 5.70 and 5.95 ppm, and a broad singlet for the protons of the amino group at 6.82 or 7.35 ppm.
R
N
O
CN
CN
O
CN
R
O
N
Et3N
O
+
OH
MeCN, 60°C
NH2
O
Me
O
Me
Me
O
Me
3a-c
1
4a-c
3, 4 a R = H, b R = Me, c R = Et
Since the carbon atom at position 4 of the pyran ring in compounds 2 and 4 is asymmetric, the
introduction of a diastereotopic group into the molecule would make it possible to detect its presence in the
1H NMR spectrum. In fact the signal for the diastereotopic methylene of the N-ethyl fragment in the spectrum of
compound 4c is complicated and represents a doublet of quartets and not the usual quartet.
The IR spectra of compounds 4a-c contain absorption bands corresponding to the vibrations of the N–H
bonds of the amino group at 3273 and 3153 cm-1, the nitrile group at 2180 cm-1, the carbonyl of the isatin
fragment at 1693 cm−1, and the conjugated carbonyl at 1653 cm-1.
With the ninhydrin derivative the reaction probably takes place in a more complicated way in so far as
under standard conditions the reaction mixture becomes very dark, and a poorly soluble dark tarry precipitate
that could not be purified separates. Cyclohexylidene malononitrile exhibited low reactivity; even when the
reaction mixture was kept for several days, according to TLC, it contained significant amounts of unreacted
hydroxytropone 1 and a complex mixture of several products, which could not be separated or identified.
138

As already mentioned, on the basis of the enamino nitrile fragment of 2-amino-3-cyano-4H-pyrans it is
possible to form more complex pyrimidine-, pyrido-, or pyrazolo-condensed systems.
TABLE 2. The Spectral Characteristics of the Synthesized Compounds
IR spectrum,
Com-
pound
1Н NMR spectrum, δ ppm (J, Hz)*
ν, cm-1
1
2
3
2a
3286, 3153, 2180,
1666, 1593, 1540,
1500, 1240, 1206
2.60 (3Н, s, 10-CH3); 2.72 (3Н, s, 8-CH3); 3.72 (3Н, s, OCH3);
4.25 (1Н, s, H-4); 6.05 (1Н, d, J = 13, H-6);
6.43 (1Н, d, J = 13, H-5); 6.90 (2Н, d, J = 9, H-3'+H-5');
7.00 (2Н, br. s, NH2); 7.15 (2Н, d, J = 9, H-2'+H-6')
2b
3286, 3140, 2180,
1673, 1633, 1600,
1533, 1246, 1200
1.38 (3Н, t, J = 8, OCH2CH3); 2.70 (6Н, s, 8-CH3+10-CH3);
4.00 (2Н, q, J = 8, OCH2CH3); 4.20 (1Н, s, H-4);
4.48 (2Н, br. s, NH2); 6.12 (1Н, d, J = 13, H-6);
6.30 (1Н, d, J = 13, H-5); 6.82 (2Н, d, J = 9, H-3'+H-5');
7.15 (2Н, d, J = 9, H-2+H-6')
2c
2d
2e
3286, 3140, 2180,
1673, 1600, 1553,
1200
2.50 (3Н, s, SCH3); 2.75 (6Н, s, 8-CH3+10-CH3); 4.28 (1Н, s, H-4);
4.57 (2Н, br. s, NH2); 6.20 (1Н, d, J = 13, H-6);
6.35 (1Н, d, J = 13, H-5); 7.22 (2H, d, J = 9, H-3'+H-5');
7.28 (2Н, d, J = 9, H-2'+H-6')
3300, 3166, 2186,
1673, 1600, 1553,
1500, 1206
2.68 (6H, s, 8-CH3+10-CH3); 4.23 (1H, s, H-4); 4.50 (2H, br. s, NH2);
6.13 (1H, d, J = 13, H-6); 6.26 (1H, d, J = 13, H-5);
7.02 (2H, dd, J = 9, J = 9, H-3'+H-5');
7.19 (2H, dd, J = 9, H-2'+H-6')
3326, 3193, 2193,
1673, 1633, 1606,
1540, 1213
2.60 (3Н, s, 10-CH3); 2.72 (3Н, s, 8-CH3); 4.39 (1Н, s, H-4);
6.06 (1Н, d, J = 13, H-6); 6.47 (1Н, d, J = 13, H-5);
7.10 (2Н, br. s, NH2); 7.22 (2Н, d, J = 9, H-3'+H-5');
7.55 (2Н, d, J = 9, H-2'+H-6')
2f
3313, 3160, 2186,
1673, 1600, 1553,
1500, 1206
2.60 (3Н, s, 10-CH3); 2.72 (3Н, s, 8-CH3); 4.60 (1Н, s, H-4);
6.07 (1Н, d, J = 13, H-6); 6.43 (1Н, d, J = 13, H-5);
7.10 (2Н, br. s, NH2); 7.15-7.35 (4Н, m, H-3'+H-4'+H-5'+ H-6')
2g
2h
3313, 3180, 2186,
1673, 1600, 1553,
1206
2.60 (3Н, s, 10-CH3); 2.72 (3H, s, 8-CH3); 4.83 (1Н, s, H-4);
6.05 (1Н, d, J = 13, H-6); 6.28 (1Н, d, J = 13, H-5);
7.05 (2H, br. s, NH2); 7.18-7.48 (4Н, m, H-3'+H-4'+H-5'+ H-6')
3286, 3140, 2180,
1673, 1633, 1600,
1533, 1246, 1200
2.61 (3H, s, 10-CH3); 2.71 (3H, s, 8-CH3); 4.27 (1H, s, H-4);
5.99 (2H, s, OCH2O); 6.07 (1H, d, J = 13, H-6);
6.50 (1H, d, J = 13, H-5); 6.70-6.78 (2H, m, H-4'+H-7');
6.87 (1H, d, J = 8, H-6'); 7.00 (2H, br. s, NH2)
2i
3313, 3180, 2186,
1673, 1600, 1553,
1206
2.68 (3H, s, 10-CH3); 2.70 (3H, s, 8-CH3); 4.60 (2H, br. s, NH2);
4.90 (1H, s, H-4); 6.12 (1H, d, J = 13, H-6);
6.20 (1H, d, J = 13, H-5); 7.14 (1H, d, J = 8, H-6');
7.22 (1H, dd, J = 8, J = 2, H-5'); 7.40 (1H, d, J = 2, H-3')
2j
3300, 3153, 2186,
1673, 1593, 1553,
1206
2.62 (3Н, s, 10-CH3); 2.72 (3H, s, 8-CH3); 4.34 (1Н, s, H-4);
6.05 (1Н, d, J = 13, H-6); 6.50 (1Н, d, J = 13, H-5);
7.03 (2H, br. s, NH2); 7.20-7.38 (5Н, m, C6H5)
2k
3433, 3140, 2180,
1673, 1633, 1600,
1553, 1193
2.61 (3Н, s, 10-CH3); 2.68 (3Н, s, 8-CH3); 4.72 (1Н, s, H-4);
6.12 (1Н, d, J = 13, H-6); 6.67 (1Н, d, J = 13, H-5);
6.95 (1Н, dd, J = 5, J = 3, H-4'); 7.03 (1Н, d, J = 3, H-3');
7.13 (2Н, br. s, NH2); 7.43 (1Н, d, J = 5, H-5')
4a
3273, 3153, 2180,
1693, 1653, 1600,
1553, 1206
2.60 (3H, s, 10-CH3); 2.73 (3H, s, 8-CH3); 5.75 (1H, d, J = 13, H-6);
6.05 (1H, d, J = 13, H-5); 6.92 (1H, d, J = 8, H-7');
7.05 (1H, t, J = 8, H-5'); 7.18-7.38 (4H, m, NH2+H-4'+H-6');
10.75 (1H, s, CO–NH)
4b
4c
3273, 3153, 2180,
1693, 1653, 1600,
1553, 1206
2.62 (3H, s, 10-CH3); 2.73 (3H, s, 8-CH3); 3.20 (3H, s, N–CH3);
5.70 (1H, d, J = 13, H-6); 5.95 (1H, d, J = 13, H-5);
7.08-7.19 (2H, m, H-7'+H-5'); 7.23–7.45 (4H, m, NH2+H-4'+H-6')
3270, 3153, 2186,
1693, 1653, 1600,
1206
1.20 (3H, t, J = 7, CH2CH3); 2.63 (3H, s, 10-CH3);
2.75 (3H, s, 8-CH3); 3.80 (2H, dq, J = 7, J = 10, CH2CH3);
5.67 (1H, d, J = 13, H-6); 5.96 (1H, d, J = 13, H-5);
6.82 (2H, br. s, NH2); 7.07–7.17 (2H, m, H-7'+H-5');
7.25 (1H, d, J = 8, H-4'); 7.40 (1H, t, J = 8, H-6')
139

TABLE 2. (continued)
1
2
3
5
7
2193, 1660, 1626,
1606, 1560, 1233,
1180
1.37 (3Н, t, J = 7, CH2CH3); 2.68 (6Н, s, 10-CH3+8-CH3);
3.77 (3Н, s, OCH3); 4.28 (1Н, s, H-4); 4.38 (2Н, q, J = 7, CH2CH3);
6.13 (1Н, d, J = 13, H-6); 6.28 (1Н, d, J = 13, H-5);
6.87 (2Н, d, J = 8, H-3'+H-5'); 7.18 (2Н, d, J = 8, H-2'+H-6');
8.24 (1Н, s, CH=N)
3393, 3153, 1653,
1606, 1540, 1260,
1193
2.61 (3H, s, 1-CH3); 2.83 (3H, s, 3-CH3); 3.68 (3H, s, OCH3);
4.75 (1H, s, H-7); 6.12 (1H, d, J = 13, H-5);
6.57 (1H, d, J = 13, H-6); 6.82-6.90 (4H, m, NH2+H-3'+H-5');
7.30 (2H, d, J = 9, H-2'+H-6'), 8.12 (1H, s, H-10)
_______
1
* The H NMR spectra were recorded in DMSO-d6 (compounds 2a, e-h,
j,k, 4a-c, 7) and CDCl3 (compounds 2b-d, i, 5).
In the case of compound 2a we were able to realize the synthesis of the corresponding annulated
4-aminopyrimidine in two stages. First, the corresponding ethoxymethylene derivative 5 was obtained by boiling
the initial pyran 2a in triethyl orthoformate for an hour. Its solution in alcohol was then treated with aqueous
ammonia. After standing at room temperature for two days the aminopyrimidine 7 was isolated.
In the 1H NMR spectrum of compound 7 there is a signal for the methine proton of the pyrimidine ring at
8.1 ppm and also a broad signal for the amino group at 6.9 ppm, partly overlapping with the signal of the protons
of the aryl group. Further evidence for the cyclization that occurs is the absence of the absorption band of the
C≡N bond in the region of ~2180-2193 cm−1, which is present in the spectrum of the initial pyran 5.
Ar
Ar
CN
N
CN
HC(OEt)3
O
O
O
O
NH2
OEt
Me
Me
O
O
5
2a
Me
Me
NH3(aq)
EtOH
Ar
Ar
NH2
N
CN
O
O
O
N
O
N
NH2
Me
Me
O
O
Me
Me
7
6
5-7 Ar = 4-MeOC6H4
Thus, 8-hydroxy-1,3-dimethyl-4H-cyclohepta[c]furan-4-one (1) exhibits high nucleophilic reactivity in
reaction with ylidene malononitriles. These reactions lead to the formation of the expected respective condensed
2-amino-3-cyano-4H-pyrans, including spirocyclic compounds. The obtained pyrans can be converted into
pyranopyrimidines in two stages.
140

EXPERIMENTAL
1
The IR spectra were recorded in vaseline oil on a Specord IR-71 spectrometer. The H NMR spectra
were recorded on Bruker DPX-250 (250 MHz) and Varian VXR-300 Unity (300 MHz) spectrometers in CDCl3
13
and DMSO-d6. The C NMR spectra were recorded on a Varian VXR-300 Unity spectrometer (75.5 MHz) in
DMSO-d6 with TMS as internal standard.
The required 8-hydroxy-1,3-dimethyl-4H-cyclopenta[c]furan-4-one (1) was obtained by the previously
developed method [11]. The ylidene malonitriles were prepared by the Knoevenagel reaction of malononitrile
and the corresponding aldehyde or ketone according to the described procedures.
2-Amino-4-((het)aryl)-8,10-dimethyl-7-oxo-4H,7H-furo[3′,4′:6,7]cyclohepta[1,2-b]pyran-3-carbo-
nitriles 2a-k and 2-Amino-8,10-dimethyl-2′,7-dioxo-1′,2′-dihydro-7H-spiro[furo[3′,4′:6,7]cyclohepta-
[1,2-b]pyran-4,3′-indole]-3-carbonitriles 4a-c (General Method). To a suspension of the hydroxytropone 1
(1.9 g, 10 mmol) in acetonitrile with stirring we added the ylidene malononitrile (10 mmol) and triethylamine
(0.1 ml), and we heated the mixture to 50-60°C. In most cases a precipitate of the product began to separate after
3-5 min. The reaction mixture was left at room temperature overnight. The product was filtered off, washed with
acetonitrile, and recrystallized from a mixture of acetonitrile and DMF or from dichloroethane. The yields of the
13
products amounted to 32-82%. The characteristics of the obtained compounds are given in Table 1. C NMR
spectrum for 2b: 14.3, 14.7, 16.3, 42.6, 57.4, 63.0, 111.1, 111.8, 114.7 (2С); 119.5, 119.8, 128.8 (2С); 129.4,
13
136.7, 137.6, 146.3, 151.1, 156.5, 157.7, 158.1, 183.6. C NMR spectrum for 4b: 14.1, 16.5, 26.6, 51.7, 54.9,
107.4, 109.3, 111.5, 117.6, 119.5, 123.7, 124.8, 129.7, 130.2, 133.2, 133.9, 143.3, 148.1, 152.2, 156.7, 159.0,
176.7, 183.4.
2-Amino-4-(4-methoxyphenyl)-8,10-dimethyl-7-oxo-4H,7H-furo[3′,4′:6,7]cyclohepta[1,2-b]pyran-
3-carbonitrile 2a (from hydroxytropone, aldehyde, and malononitrile). To a mixture of compound 1 (1.9 g,
10 mmol), 4-methoxybenzaldehyde (12 ml, 10 mmol), and malononitrile (0.66 g, 10 mmol) in acetonitrile with
stirring was added triethylamine (0.1 ml), and we heated the mixture to 50-60°C. A precipitate of the product
began to separate after 1-2 min. The reaction mixture was left at room temperature overnight. The product was
filtered off, washed with acetonitrile, and crystallized twice from a mixture of acetonitrile and DMF. The yield
was 62%.
2-(1-Ethoxymethyleneamino)-4-(4-methoxyphenyl)-8,10-dimethyl-7-oxo-4H,7H-furo[3′,4′:6,7]cyclo-
hepta[1,2-b]pyran-3-carbonitrile (5). A suspension of the pyran 2a (0.5 g, 1.3 mmol) was boiled in triethyl
orthoformate (10 ml) for 1.5 h. The solution was evaporated to dryness. The residue was dissolved in chloroform
and passed through a small column of aluminum oxide, eluted with chloroform, and evaporated. The residue was
crystallized from a 1:1 mixture of toluene and petroleum ether.
8-Amino-7-(4-methoxyphenyl)-1,3-dimethyl-4H,7H-furo[3″,4″:3′,4′]cyclohepta[1′,2′:5,6]pyrano-
[2,3-d]pyrimidin-4-one (7). A suspension of the pyran 2a (0.5 g, 1.3 mmol) in triethyl orthoformate (10 ml) was
boiled for 1.5 h and evaporated to dryness. The residue was dissolved in chloroform and passed through a
column of aluminum oxide and eluted with chloroform. The eluate was evaporated. The residue was dissolved
with gentle heat (40-50°C) in ethanol (15 ml), and aqueous ammonia (0.5 ml) was added. The flask was covered
and kept at room temperature for two days. The precipitate was filtered off and purified by recrystallization from
ethanol.
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