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Syntheses of Heterocyeles, 191 Reactions of /3-Aminocrotononitrile with Heterocyclic Phenolic Compounds

F A R I D S . G . S O L I M A N * a n d T H O M A S K A P P E

Institute of Organic Chemistry, University of Graz, Austria

(Z. Naturforsch. 31b, 495-499 [1976]; received November 12,1975)

/S-Aminocrotononitrile, 4-Hydroxycoumarin, 4-Hydroxycarbostyril, 4-Hydroxy-2-pyrones, 4-Hydroxy-2-pyridones

Condensation of /5-aminocrotononitrile (2a) with 4-hydroxycoumarin (la, X = 0 , R = R 2 =H, Ri = OH) afforded the tricyclic compound 7 and the bicyclic compound 11a from 4-hydroxy-6-methyl-2-pyrone (4). Analogous compounds could not be obtained from 4-hydroxy-6-methyl-2-pyridone (5) or 4-hydroxycarbostyril (6) due to the failure of the resulting condensation products 12 a and 13, respectively to undergo intramolecular cyclization. The structures assigned to 7, 11a, 12 a, 13, as well as to 5-eyano-4,6-dimethyl-2-pyridone (14), obtained by self-condensation of j5-aminocrotononitrile, were substantiated by spectroscopic studies.

Substituted acetonitriles are known to condense with phenols giving the corresponding imino-coumarins and/or coumarins (1). 3-Cyano-4-methyl-imino-coumarin ( 1 , X = N H , R = C N , R I = R 2 = H ) I

and 3-substituted-3-aminocoumarins ( 1 , X = N H ,

R 1 = R 2 = H ) 2 - 4 have been obtained by the base-catalysed condensation of 2-hydroxyacetophenone or salicylaldehyde, respectively with substituted nitriles. On the other hand, S A T O 5 condensed benzoylacetonitrile with resorcinol or its mono-methyl ether in presence of two equivalents of anhydrous aluminum chloride in isopropyl ether saturated with hydrogen chloride and obtained 2-imino-4-phenylumbelliferone hydrochloride (1, X = N H , R = H , R I = C 6 H 5 , R 2 = 7 - O H ) or its methyl ether. In absence of the inert solvent, excess of m-cresol yielded the corresponding iminocoumarin hy-drochloride, whereas p-cresol afforded 6-methyl-4-phenylcoumarin (1, X = 0 , R = H , Ri=C6H5, R2=6-CH3). In a trial to avoid the polymerization of acetoacetonitrile with anhydrous aluminium chloride and hydrogen chloride, these authors effected its condensation with resorcinol, its mono-

* Present adress: Department of Pharm. Chemistry, Faculty of Pharmacy, University of Alexandria, Egypt.

Requests for reprints should be sent to Prof. Dr. TH. KAPPE, Institut für Organische Chemie der Uni-versität, A-8010 Graz, Austria.

methyl ether, or cresols using polyphosphoric acid and obtained the respective coumarins. Subse-quently, S A T O and co-workers6 condensed phenol, cresols and resorcinol with /?-aminocrotononitrile (2 a) in presence of polyphosphoric acid and obtained 6-amino-3-cyano-2,4-lutidine (3) alongside 4-methyl-coumarin derivatives. They conceived the reaction to proceed via addition of the phenols to the nitrile followed by intramolecular cyclization to imino-coumarin and subsequent acid hydrolysis.

i CH n

H 2 N / N C H 3

2 a R=CN 2b R=C02C2H5

CH3

XX H3C^N^NH2

In our attempt to build up 4-methyl-2-imino-pyrone moiety on to different heterocyclic phenolic compounds and some phenols, /3-aminocrotono-nitrile (2 a) has been used in absence of acid or basic catalysts. In this respect 2 a has been condensed with the pharmacologically active 4-hydroxy-coumarin (la, X = 0 , R = R 2 = H , R i = O H ) , 4-hydroxy-6-methyl-2 [H]-pyran-2-one (4),4-hydroxy-6-methyl-2-pyridone (5), 4-hydroxycarbostyril (6), resorcinol, orcinol, 2-naphthol and 1,3-dihydroxy-naphthalene following the conditions of K A P P E ,

B A X E V A N I D I S and Z I E G L E R 7 in which ethyl-/?-

496 F. S. G. S OLIM AN-TH. KAPPE • SYNTHESES OF HETEROCYCLES 496

aminocrotonate (2 b) was used to incorporate the 4-methyl-2[H]-pyran-2-one residue in various phe-nolic compounds.

When /3-aminocrotononitrile (2 a) was heated with 4-hydroxycoumarin ( la) at 180 °C for 30 minutes ammonia and water were liberated. The resulting nitrogenous product dissolves in dilute mineral acids and gives an acetyl derivative. Elemental analysis and mass peak showed this product and its acetate to have the molecular formulae C13H10N2O2 and C 1 5 H 1 2 N 2 O 3 , respectively. The I R spectrum of the compound showed sharp bands at 3415 cm - 1 , 3330 cm-1 and at 3195 cm"1 attributed to the NH stretching absorption and a strong broad band (1700 cm- 1 -1550 cm-1) splitted at 1660 cm-1, 1630 cm-1, 1605 cm-1 and at 1580 cm-1 followed by a sharp band at 1535 cm - 1 are due to the mixed absorption of the C = 0 , C = C , C = N and aromatics. The acetyl derivative showed the NH as weak band between 3300 cm - 1 and 2800 cm - 1 and now an additional (not associated) sharp band of the a-pyrone carbonyl at 1725 cm - 1 . The properties of this compound and its acetyl derivative are, therefore, in accord with the structures 7 and 8 (Scheme la ) , for 2-amino-4-methyl-5 H[l]-benzo-pyrano[4,3-b]pyridin-5-one and 2-acetamido-4-methyl - 5 H - [l]benzopyrano [4,3 - b] pyridin - 5 - one, respectively. Further, the NMR (6 ppm) spectrum of 7 showed a doublet CH3 protons signal at 2.65,

Scheme l a

OH

2a la

CC^Cgf^Clg

+ CH-CHjCgHg COCcHgCU

10a 0 ^ 0

10b

Scheme l b

8 -CH2C0> 7 -HCN

m/e 268 m/e 226

CH3 -H - m/e 198

-coj m/e 170

the H at C-3 as doublet at 6.15 (both J = 1 Hz), the NH2 protons at 7.0 and four multiplet aromatic protons in the region 7.10-7.95. The acetyl derivative 8 revealed the acetyl-CH3 at 2.1, the 4-CH3 signal at 2.72, the four aromatic protons between 7.0 and 7.96 overlapping the C-3 proton at 7.70, and the NH at 10.6. An isomeric compound namely, 4-amino-l-methyl-5 H-[l]benzopyrano[3,4-c]pyridin-5-one has been reported in literature8. The structure 7 is supported by the formation of 10 in 40% yield when it was heated with bis-2,4,6-trichlorophenyl benzyl-malonate (9) (Scheme la ) . The spectral data are in favour of structures 10 a and 10b. (Compare the structures of other "malonyl-a-amino-pyridines"9'10).

The predominant fragmentation process of 7 and 8 are illustrated in Scheme l b .

Heating /5-aminocrotononitrile with 4-hydroxy-6-methyl-2-[H]-pyran-2-one (4) at 150 °C for 30 minu-tes afforded a nitrogenous compound, having the formula C 1 0 H 9 N O 3 , which is assigned the structure 11a and not l i b or 11c (Scheme Ha). However,

Scheme H b

11a -m/e 191

-CO m/e 163

- H m/e 162

-CO m/e 134

l i b (4,7-dimethyl-2,5-dioxo-5,6-dihydro-2 H-pyrano[3,2-c]pyridine) has been synthesized before by condensing ethyl ^-aminocrotonate (2b) with 4-hydroxy-6-methyl-2-pyridone (5)7. Further, exclu-sion of 11c is based upon the stability of the synthesized product towards acid hydrolysis as well as the sequential loss of two molecules of C = 0 during its fragmentation in the mass spectrum (Scheme l i b ) . The I R spectrum of 11a namely, 3,8-dimethyl-2,5-dioxo-5,6-dihydro-2 H-pyrano-[4,3-b]-pyridine revealed a weak broad band in the region 3200 cm_ 1-2500 cm - 1 due to the NH stretching absorption followed by a strong band of medium intensity at 1735 cm - 1 shouldered at 1760 cm - 1

attributed to the C = 0 of the 2-pyrone. The strong broad band between 1700 cm - 1 and 1600 cm - 1

splitted at 1660 cm - 1 (strong) and at 1630 cm - 1

(medium intensity) is due to the C = 0 of the

F. S. G. S OLIM AN-TH. KAPPE • SYNTHESES OF HETEROCYCLES 497

2-pyridone and the C = C stretching absorptions. The NMR (6 ppm) spectrum showed the two methyl signals at 2.16 and at 2.41 and the two olefinic protons at 5.8 and at 5.95.

Heating ß-aminocrotononitrile (2 a) and 4-hydroxy-6-methyl-2-pyridone (5) at 230 °C for 30 minutes afforded a compound, C 1 0 H 1 1 N 3 O , which may be assigned the formula 12 a or b (Scheme III a). Structure 12 b has been excluded on the basis of spectral data. The I R spectrum clearly showed a nitrile band at 2220 cm - 1 and a very broad band of medium intensity between 3500 cm - 1 and 2400 cm - 1 attributed to the N H absorption. The broad band (1680 cm^-lSOO cm"1) splitted at 1655 cm - 1 (strong), at 1630 cm - 1 (weak), and at 1605 cm - 1 (medium) is attributed to the mixed absorption of the C = 0 , C = C and aromatics. The NMR (<5 ppm) spectrum showed the C-6 methyl protons as doublet (J — 2 Hz) at 2.15 and the a-CH3 as singlet at 2.31, and the ß-H at 6.55. Referring to the NMR spectrum of 5, the C-6 methyl appeared at 2.05, the C-3 proton at 5.25 (doublet, «7 = 2 Hz), the C-5 proton at 5.49 (dd, J = 2 Hz) and the OH at 10.65. The fragmentation of 12 a in the mass spectrum (Scheme I l l b ) indicates a C H 3 C N elimina-tion which is known to characterize eis structures11. Consequently, the pyridyl and the CN groups in 12 a have the trans configuration and formation of the hypothetical cyclic structure 12 b would not be sterically possible. In support of this view, trials to cyclize 12 a by the action of heat or sodium metal were abortive. An analogous compound, ß-(p-hydroxyphenyl)-crotononitrile, has been synthe-sized by S A T O et al.5 by the acid-catalysed reaction of phenol with benzoylacetonitrile. Apparently, the reactions leading to 7 and to 11a proceed through

ieme E l a

OH NH2 ana yCN

( S j c r c < h N^O H-jCN^O H

5

ieme M b

& 12a 1 2 b

2a E189

-CH3CN

NH5

ÄC=CH

.. 0 -co NH,

H m/e 148

rk H,C N C=CH

3 H m/e 120

-H •m/e 119

conversion of the 4-hydroxy compounds l a ( X = 0 , R = R 2 = H , R I = O H ) ; 4 and 5 to the corresponding 4-amino derivatives, subsequent formation of an intermediate acyclic nitriles such as 12 a, and intra-molecular cyclization to 7 and to 11a with loss of ammonia.

Heating 4-hydroxycarbostyril (6) with 2 a at 280 °C for 30 minutes afforded the compound C 1 7 H 1 3 N 3 O 2 which is assigned the structme 13 (Scheme IVa) on the basis of spectroscopic data.

Scheme IVa CH3

^ C = C H - C N OH 0 _ CH3

o c X — N^O H

13

J H

14

Scheme IVb

m/e 160

The I R spectrum showed a nitrile absorption band at 2220 cm - 1 , a broad band of medium intensity between 3500 cm"1 and 2400 cm"1 due to the NH, and a broad band between 1660 cm - 1 and 1500 cm - 1

peaked broadly at 1640 cm - 1 and splitted at 1590 cm - 1 with shoulders at 1660 cm - 1 and at 1510 cm - 1 due to the mixed absorption of C = 0 , C = C and aromatics. The NMR (d ppm) spectrum revealed two methyl groups signals at 2.16 (d, J = 1 Hz) and 2.35 (s), two olefinic protons at 6.01 and at 6.32 (s), three aromatic protons at C-6, 7, and 8 in the region between 6.82-7.32 (multiplet) and the C-5 proton at 7.68 (dd, J = 2 + 8 Hz). The mass spectrum (Scheme IVb) showed a mass peak at 224 indicating the loss of a crotononitrile moiety through a C - 0 cleavage followed by a mass peak at 160 due to the abundance of 4-hydroxycarbostyril ion formed by a second loss of a crotononitrile moiety. A similar C - 0 link has been reported to occur in a crotononitrile derivative obtained by condensing a-ethyl acetoacetonitrile with p-cresol of phenol in presence of anhydrous aluminum chloride and hydrogen chloride5.

On heating 2-naphthol, resorcinol or 1,3-di-hydroxynaphthalene with 2 a only tarry products were obtained. However, heating orcinol with 2 a at

498 F. S. G. S OLIM AN-TH. KAPPE • SYNTHESES OF HETEROCYCLES 498

180 °C for 30 minutes yielded a nitrogenous product whose analytical and spectral data agreed with formula C s H g ^ O having the structure 14 for 5-cyano-4,6-dimethyl-2-pyridone. Formation of this pyridone by heating ß - amino crotononit rile alone at the same temperature suggests that 2 a undergoes preferential self-condensation rather than inter-molecular condensation with the phenolic com-pounds. Previously, 14 has been obtained in the course of condensing privaldehyde with 2 a in presence of glacial acetic acid12. Variation in the temperatures adopted in effecting the above mentioned condensations is due to the differences in the melting points of the phenolic compounds utilized; otherwise autocondensation of /S-amino-crotononitrile predominates.

Experimental All melting points are corrected. IR spectra were

determined on Perkin Elmer 421 using potassium bromide pellets. NMR spectra were recorded on A 60 A Varian using DMSO-dö as solvent unless otherwise stated. Mass spectral analyses were performed on Organic MS 20 AEI (70 eV).

1. 2-Amino-4-methyl-5 H-[ 1 Jbenzopyrano [ 4,3-b]-pyridin-5-one (7)

An intimate mixture of 4-hydroxycoumarin (1 a) (0.81 g, 0.005 mole) and /3-aminocrotononitrile (2 a) (0.46 g, 0.005 mole) was placed in an oil bath previously heated to 180 °C. The melt was main-tained for 30 minutes during which water and ammonia were liberated. The dark brown mass was cooled and crystallized from ethanol with charcoal treatment to yield 0.95 g of an orange product (85%). It was then purified by recrystallization from ethanol as fine needles, m.p. 267.5-268.5 °C. It is soluble in dilute hydrochloric acid and apparently insoluble in dilute sodium hydroxide.

MS: m/e (relative abundance) 227 ( M - f l , 16); 226 (M+, 100); 225 (17); 200 (5); 199 (15); 198 (15); 170(5); 121(13); 113(5); 99(5) ; 65(5) ; 44(9) ; 43 (5). C 1 3 H 1 0 N 2 O 2

Calcd C 69.02 H 4.45 N 12.38, Found C 68.87 H 4.51 N 12.09.

2. 2-Acetamido-4-methyl-5 H-[ 1 Jbenzopyrano-[4,3-b]pyridin-5-one (8)

It was obtained in an almost quantitative yield when 7 (0.7 g) was refluxed with acetic anhydride (8 ml) for 30 minutes. The acetyl derivative which crystallized in the course of heating was separated, treated with sodium hydrogen carbonate solution and filtered. It was then crystallized from ethanol as fine needles, m.p. 283-284 °C.

MS: m/e (relative abundance) 269 (M + , 8); 268 (M+, 42); 227 (55); 226 (100); 225 (12); 199(27); 198 (23); 170 (10); 121 (11); 65 (7); 52 (6); 43 (24). C 1 5 H 1 2 N 2 O 3

Calcd C 67.15 H 4.51 N 10.44, Found C 67.30 H 4.48 N 10.30.

3. 2-Benzyl-3-hydroxy-6-methyl-l H, 7 H-[l]-benzopyranof 3',4': 5,6]pyrido[ l,2-a]-pyrimidin-1,7-dione (10 a)

A mixture of 7 (1.13 g ; 0.005 mole) and bis-2,4,6-trichlorophenyl benzylmalonate (2.78 g; 0.005 mole) was heated at 240 °C for 1 h. After cooling, the pale brown reaction product was digested with ethanol and the insoluble portion (10a) was filtered; yield 0.77 g (41%). It was purified by crystallization from dimethylformamide then from pyridine as pale yellow crystals, m.p. 297.5-299.5 °C (decomp.).

Its I R spectrum is characterized by the OH stretching absorption between 3540 cm - 1 and 2600 cm - 1 , and a strong broad band located between 1750 cm-1 and 1500 cm - 1 shouldered at 1730 cm - 1 and at 1705 cm - 1 attributed to the mixed absorption of the C = 0 , C = C , C = N and aromatics. The NMR (d ppm) in trifluoroacetic acid: 3.12 (s, CH3); 3.78 (s, CH2); 6.75-7.82 (m, nine aromatic protons); 7.11 (s, olefinic proton).

MS: m/e (relative abundance) 385 ( M + l , 26); 384 (M+, 100); 383 (M—1, 10); 369 (5); 368 (5); 355 (6); 327 (5); 307 (8); 294 (15); 293 (M-C6H5CH2-, 83); 279 (10); 264 (10); 253 (5); 196 (6); 131 (5); 93 (15); 91 (8); 77 (8); 44 (8). C23H16N2O4

Calcd C 71.87 H4.19 N 7.28, Found C 71.73 H4.18 N 7.57.

4. 3,8-Dimethyl-2,5-dioxo-5,6-dihydro-2 H-pyranof4,3-b]-pyridine (11a)

A mixture of 4-hydroxy-6-methyl-2[H]pyran-2-one (4) (3.78 g, 0.03 mole) and 2a (2.76 g, 0.03 mole) was heated at 150 °C in an oil bath for 30 minutes. After cooling, the dark brown reaction mixture was warmed with ethanol and filtered. The brownish-red insoluble product was then purified by recrystalliza-tion from dimethylformamide as brownish-red microcrystals, m.p. above 340 °C; yield 1.2 g (36.6%). It remained unchanged upon treatment with boiling 2 N hydrochloric acid.

MS: m/e (relative abundance) 192 (M + l , 14); 191 (M+, 93); 164 (10): 163 (100); 162 (28); 135 (10); 134 (73); 117 (10); 116 (13); 82 (13); 65 (10); 53 (17); 52 (17); 51 (10); 44 (13); 42 (28). C 1 0 H 9 N O 3

Calcd C 62.83 H 4.74 N 7.33, Found C 62.82 H 4.91 N 7.71.

5. 3-(4-Amino-6-methyl-2-oxo-l,2-dihydro-3-pyridyl)-erotononitrile (12 a)

A powdered mixture of 4-hydroxy-6-methyl-2-pyridone (5) (1.25 g, 0.01 mole) and ß - amino crotono-

F. S. G. S OLIM AN-TH. KAPPE • SYNTHESES OF HETEROCYCLES 499

nitrile (0.92 g, 0.01 mole) was heated at 230 °C to effect melting then the temperature of the melt was maintained at 190 °C for 30 minutes. After cooling, the product was extracted from the dark brown mass comprising unreacted 5 and any other products with a large volume of boiling benzene. A yellow impure crystalline product separated out after con-centrating and cooling; yield 0.65g (22%). Repeated crystallizations from benzene afforded a yellow microcrystalline substance which has no definite melting point but darkens at 192 °C and decomposes between 242 and 252 °C.

MS: m/e (relative abundance) 189 (M+, 20); 170 (20); 169 (20); 163 (13); 149 (20); 148 (87); 147 (20); 120 (47); 119 (100); 105 (20); 98 (20); 97 (20); 95 (20); 85 (27); 84 (27); 83 (33); 81 (27); 73 (33); 71 (33); 69 (53); 67 (27); 60 (33); 57 (66); 55 (66); 45 (67); 44 (100); 43 (73); 42 (33); 41 (67). C 1 0 H 1 1 N 3 O

Calcd C 63.47 H 5.85 N 22.20, Found C 62.64 H 5.45 N 21.61.

6. 3-[4- (l-Cyano-2-,pro'penyloxy)-2-oxo-l,2-dihydro-3-quinolinyl]-crotononitrile (13)

An intimate mixture of 4-hvdroxycarbostyril (6) (3.22 g, 0.02 mole) and 2a (1.84 g, 0.02 mole) was heated at 280 °C for 30 minutes. The dark brown reaction product was then extracted with a large volume of boiling ethanol and after filtration and evaporation, the extract yielded 1.5 g (26%) of crude product. It was then obtained upon repeated crystallizations from ethanol as microcrystals, m.p. 288-291 °C (decomp.).

MS: m/e (relative abundance) 224 (M—67, 4); 223 (4); 161 (23); 160 (96); 149 (12); 148 (100); 133 (21); 132 (28); 131 (12); 120 (49); 119 (100); 118 (9); 105 (26); 104 (17); 92 (12); 91 (5); 78 (10); 77 (12); 76 (8); 66 (10); 65 (10); 64 (5); 63 (5).

1 H. JUNEK, Monatsh. Chem. 95, 234 [1964]. 2 R . K U H N and D. W E I S E R , Liebigs Ann. Chem. 6 0 0 ,

1 4 4 [ 1 9 5 6 ] . 3 G . P. SCHIEMENZ , Chem. Ber. 95, 483 [1962]. 4 H . J U N E K , Monatsh. Chem. 9 4 , 1 9 2 [ 1 9 6 3 ] . 5 K. SATO and T. A M A K A S U , J. Org. Chem. 33, 2446

[1968]. 6 K . SATO , M . OHASHI , T . A M A K A S U , a n d K . T A K E D A ,

Bull. Chem. Soc. Japan 42, 2319 [1969], 7 T H . K A P P E , G . B A X E V A N I D I S , a n d E . Z I E G L E R ,

Monatsh. Chem. 1 0 2 , 1 3 9 2 [ 1 9 7 1 ] .

C 1 7 H 1 3 N O 2

Calcd N 14.42, Found N 15.28.

7. 5-Cyano-4,6-dimethyl-2-,pyridone (14) It was prepared in an almost quantitative yield

upon heating 2 a (1 g) at 180 °C for 30 minutes, and crystallized from ethanol as needles, m. p. 299-301 °C (decomp.)12. It was also obtained when orcinol (1.24 g, 0.01 mole) and 2a (0.92 g, 0.01 mole) were heated together at the same temperature for 30 minutes. Its I R spectrum revealed the N H between 3180 cm - 1 and 2400 cm - 1 and the nitrile band at 2220 cm - 1 . The broad strong band located in the region 1750 cm - 1 -1500 cm - 1 peaked at 1660 cm-1 and shouldered at 1730 cm"1, 1615 cm-1

and at 1560 cm - 1 is due to the mixed absorption of the C = 0 , C = C and aromatics.

NMR (<5 ppm) spectrum: 2.20 (s, CH3); 2.4 (s, CH3); 6.15 (s, H at C-3).

MS: m/e (relative abundance) 149 ( M + l , 10); 148 (M+, 100); 120 (M-CO, 48); 119 (M-28 + 1, 89); 105 (18); 78 (17); 65 (7); 52 (10); 51 (17); 44 (10); 42 (23).

C8H8N2O Calcd N 18.90, Found N 18.97.

One of us (F. S. G. Soliman) thanks the Austrian Ministry of Science for a maintenance grant and the University of Alexandria, Alexandria, Egypt, for a study-leave. Thanks are also due to Professor Dr. E. Z I E G L E R , Head of the Institut für Organische Chemie der Karl-Franzens-Universität Graz, Austria, for affording research facilities.

8 S. A K I O , M. H I R O S H I , and H . Y A S U A , Bull. Chem. Soc. Japan 43, 2925 [1970].

9 A. R. K A T R I T Z K Y and A. J. W A R I N G , J. Chem. Soc. 1962, 1544.

1 0 T H . K A P P E , P. F . F R I T Z , and E. Z I E G L E R , Monatsh. Chem. 102, 412 [1971].

11 M. C. H A N M I N G and N. G. F O S T E R , Interpretation of Mass Spectra of Organic Compounds, p. 303, Academic Press New York and London 1972.

12 B. L O E V and K . M. S N A D E R , J. Org. Chem. 30, 1914 [1965].