Effect of Microwave Irradiation on the Condensation of 6-Substituted 3-Formylchromones with Some Five-membered Heterocyclic Compounds

Lacova, Margita; Gasparova, Renata; Loos, Dusan; Liptay, Tibor; Pronayova, Nada

doi:10.3390/50200167

Open AccessArticle

Effect of Microwave Irradiation on the Condensation of 6-Substituted 3-Formylchromones with Some Five-membered Heterocyclic Compounds

by

Margita Lacova

^1,*,

Renata Gasparova

¹,

Dusan Loos

^1,*,

Tibor Liptay

² and

Nada Pronayova

²

¹

Department of Organic Chemistry, Faculty of Natural Sciences, Comenius University, Mlynska dolina CH-2, SK-842 15 Bratislava, Slovak Republic

²

Central Laboratories, Faculty of Chemical Technology, Slovak University of Technology, SK-812 37 Bratislava, Slovak Republic

^*

Authors to whom correspondence should be addressed.

Molecules 2000, 5(2), 167-178; https://doi.org/10.3390/50200167

Submission received: 14 October 1999 / Published: 19 February 2000

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Abstract

:

Different types of 3-substituted 4H-4-oxobenzopyrans were prepared by microwave irradiation as well as by a classical method. The beneficial effect of microwave irradiation on the aldol condensation of 3-formylchromones with 2-imino-1-methyl-imidazolidine-4-one (creatinine), 2-thioxoimidazolidine-4-one (thiohydantoin) and 2-ethyl-2-thioxothiazolidin-4-one (3-ethylrhodanine) in different reaction media is described. Our results show that the effect of microwave irradiation on the reactions studied was a shortening of the reaction times and a smooth increase in the yields. The subsequent reactions of the product with some nucleophiles are discussed. The structure of the products was proven by elemental analysis, IR and NMR spectra.

Keywords:

Creatinine; thiohydantoin; rhodamine; carbamoic acids; guanidine derivatives; Diels - Alder reaction; IR; ¹H NMR; ¹³C NMR

Introduction

This study is a continuation of our earlier publications [1,2,3,4,5,6,7], in which we described the theoretical, spectral and biological properties of newly synthesized chromone and chromanone derivatives. The aim of this work was the preparation of some new five-membered nitrogen heterocyclic derivatives of chromone as potentially useful intermediates for synthesis.

3-Formylchromones 1 were chosen as being synthetically versatile molecules with a reactive carbonyl group. They have considerable significance for their biological activities [8,9,10] and for their reactivity towards nucleophiles which allows the synthesis of a wide variety of heterocycles. A study of the influence of microwave irradiation on the condensation reactions was the next goal of this paper. Five-membered ring heterocycles 2-4 are known as precursors of α-amino acids and they can be condensed easily with aldehydes. It is known that condensations of creatinine with aldehydes [11, 12] as well as the Gränacher synthesis [13] with rhodanine under classical conditions take several hours at high temperatures (160–180°C).

As we have shown before [14], microwave irradiation is a suitable method for shortening the duration of condensation reactions. Condensations of creatinine [15] and thiohydantoin [16] with aromatic aldehydes without a solvent under microwave irradiation and giving good yields of products were described by Villemin and al. The starting 3-formylchromones used in this work are accessible via Vilsmeier-double formylation of appropriate o-hydroxyacetophenones [17]. Commercially available nitrogen heterocycles were used for the reactions. The reactions are outlined in Scheme 1 and Scheme 2. Details of the experimental results are listed in Table 1.

Results and Discussion

2-Acetamido-1-methyl-5-[(6-R-4-oxo-4H-benzopyran-3-yl)methylidene]-4,5-dihydroimidazol-4-ones 5a-5f were obtained by condensations of 1a-1f with creatinine 2 in acetic anhydride, both under microwave irradiation (A) and classical (B) conditions. Although the yields by both methods were almost the same (46-84%), the reactions in a microwave oven were considerably faster (Table 1). Imino derivatives 6a-6e (2-imino-1-methyl-5-[(6-R-4-oxo-4H-[1]-benzopyran-3-yl) methylidene]- imidazoli-din-4-ones) were obtained using dimethylsulfoxide as a solvent and boric acid as a catalyst by both methods A and B.

A convenient synthesis of carbamoic acid derivatives 7 (1-methyl-4-oxo-5-[(6-R-4-oxo-4H-[1]-benzopyran-3-yl)methylidene]-4,5-dihydroimidazol-2-carbamoic acids) was accomplished by reaction of creatinine with ethylchloroformate in N,N-dimethylformamide followed by the subsequent addition of aldehydes 1a-1e. The hydrolyzed products 7a-7e were obtained in 69-71% yields by both the classical and microwave irradiation condensation methods, even under anhydrous conditions. It is evident that compounds 7 resulted from the utilization of the water of condensation for the hydrolysis process. In the ¹H NMR spectra of compounds 7 no signals for the ethyloxy group were observed (Table 2).

3-Formylchromone condensations with thiohydantoin 3 and 3-ethylrhodanine 4 were carried out in acetic anhydride in the presence of potassium acetate under both irradiation and classical conditions. The yields of 2-thioxo-5-[(6-R-4-oxo-4H-[1]-benzopyran-3-yl) methylidene]imidazolidin-4-ones 8a-8e and 2-thioxo-5-[(6-R-4-oxo-4H-benzopyran-3-yl)methylidene]thiazolidin-4-ones, 9a and 9b, respectively, were comparable by both methods.

Attempts to hydrolyze the condensation products with diluted mineral acids to prepare ring opened heterocycles were unsuccessful. The 5-(2-hydroxyphenyl)-4-(hydroxy-methylidene)-2-(1-methyl-guanidino)-2-pentenoic acid hydrolysis products (10) were obtained only by refluxing compounds 5 in concentrated hydrochloric acid. We propose the structure of compounds 10, which contain guanidinyl, carboxyl and enolic groups on the basis of ¹H NMR, ¹³C NMR spectra and elemental analysis. Compounds 10 could be regarded as a mixtures of isomers with a very fast tautomeric equilibrium of both enolic and oxo groups. The assumption of this fast tautomeric equilibrium is supported by the data for the shift signals of C-9 in the ¹³C NMR spectra.

We next attempted to carry out Diels - Alder reactions with various dienophiles, using e.g. maleic anhydride, diethyl maleate and tetracyanoethylene, using both the classical and microwave irradiation procedures. Only heating and stirring a mixture of 5b in toluene with an excess of maleic anhydride at 40°C over 15 hr. was successful and the spiroheterocyclic adduct spiro[(1´-methyl-2´-imido-4´-oxo)-1´, 3´-diazolane-5´, 2-(7-methyl-9-oxo-2, 3, 4, 4a tetrahydroxantene)]-3, 4-dicarboxylic acid (11) was formed in 64% yield. The proposed structure was confirmed by ¹³C NMR. Similar Diels - Alder reactions were reported previously [18]. The use of microwave irradiation for the Diels - Alder experiments was unsuccessful.

All condensation products are stable solid compounds, rather insoluble in common solvents, with high melting points. Because of their poor solubility in DMSO we had to measure their ¹H NMR spectra at elevated temperatures (Table 2). The resonance signals and their multiplicity confirmed the proposed structures. The infrared spectra of the prepared compounds 5-9 showed strong absorption bands of the C=O stretching vibrations in two very well distinguished regions 1645 - 1668 cm⁻¹ and 1688 - 1745 cm⁻¹ (Table 3). The absorption bands in the lower region of the spectra belong to the ν(C=O) of the γ-pyrone ring. The higher region was attributed to the azole heterocyclic part of the prepared compounds. Compounds 10 lacked the ν(C=O) band at 1640 - 1660 cm⁻¹. Strong bands around 1740 cm⁻¹ confirmed the presence of unsaturated aldehyde groups (Table 4).

Experimental

General

Products were characterized by elemental analyses (Table 1), NMR spectra (Table 2) and IR spectra (Table 3 and Table 4). The melting points were determined on a Kofler block and are uncorrected. Infrared spectra of nujol suspensions were recorded in 400 - 4000 cm⁻¹ region on a Specord IR 75 spectrometer (Zeiss Jena). ¹H and ¹³C NMR spectra were measured on a 300 MHz spectrometer VARIAN GEMINI 200 in deuterated DMSO at 50-80°C. All microwave assisted reactions were carried out in a Lavis - 1000 multi Quant microwave oven. The apparatus was adapted for laboratory applications with magnetic stirring and an external reflux condenser.

Synthesis of 5a-5f , 8a-8e and 9a, 9b

Method A

A mixture of 6-R-3-formylchromones 1a-1f (2.87 mmol), creatinine 2 (or thiohydantoin 3 or 3-ethylrhodanine 4) ( 2.87 mmol) in dry acetic anhydride (2 cm³) in the presence of freshly fused potassium acetate was stirred and irradiated in a microwave oven for the time given in Table 1. The solid was filtered off. The products were recrystallized from dioxane or toluene.

Method B

A mixture of the same composition as in method A was heated at 110-120°C for the time given in Table 1. Isolation of products was accomplished as described in method A.

Synthesis of 6a–6e

Method A

A mixture of 6-R-3-formylchromone 1 (2.87 mmol), creatinine 2 (2.87 mmol), a catalytic amount of H₃BO₃ (20 mg) in 1cm³ of dry dimethyl sulfoxide was stirred and irradiated at 270 W in a microwave oven. The solid product was filtered off and recrystallized from dioxane or toluene.

Method B

A mixture of the same composition as in method A was heated in 1cm³ of dry dimethyl sulfoxide at 120°C over 3 h. The solid product was filtered off and recrystallized from dioxane.

Synthesis of 7a, 7b

Method A

Creatinine 2 (2.87 mmol) was dissolved in 1 cm³ of dry dimethylformamide and then ethyl chloroformate was added to the solution. The mixture was stirred and irradiated in a microwave oven at 270 W. The solid product was filtered off and recrystallized from dioxane or toluene.

Method B

The mixture of creatinine 2 ( 2.87 mmol) and ethyl chloroformate ( 3.0 mmol ) in dry dimethyl-formamide ( 1 cm³) was stirred at room temperature for 3h and then 6-R-3-formylchromone 1 ( 2.87 mmol) was added to the mixture and heated at 90°C for 6 h. The isolation of products was the same as described above.

Acid hydrolysis of compounds 5a, 5e and 5f

The solution of 0.3 g (1 mmol) creatinine derivative 5a (or 5e, 5f) in 10 ml of concentrated hydro-chloride acid was heated at 90-100°C for 4 h. After cooling the resulting white crystals were filtered off, washed with cold water and recrystallized from dioxane. Thus prepared were compounds 10a, 10e and 10f

¹³C NMR spectral data for compound 10e [δ(ppm); DMSO - d₆, 300 MHz]

C-1	C-2	C-3	C-4	C-5	C-6	C-7
155.45	123.77	123.65	154.87	107.95	120.11	174.53
C-8	C-9	C-10	C-11	C-12	C-13	C-14
114.78	157.60	109.79	130.04	163.32	28.69	149.23

Diels - Alder reaction of compound 5b with maleic anhydride (11)

The mixture of 1g (2.51 mmol) of compound 5b and 0.52 g (5.02 mmol) of maleic anhydride in toluene (30 cm³) was heated at 40°C for 15 h. The solid adduct after cooling was filtered off, washed with 10 cm³ of toluene and dried. The product was suspended in 30 cm³ water was then stirred at 40°C for 3 h. The solid acid was removed by suction and recrystallized from ethanol. Yield 64%.

¹³C NMR spectral data for compound 11 [δ(ppm); DMSO - d₆, 300 MHz]

C-1	C-1a	C-2	C-3	C-4	C-4a	C-5
131.1	131.6	107.8	39.2	39.2	135.8	116.0
C-6	C-7	C-8	C-8a	C-9	C-10a	C-11
135.7	130.9	124.6	153.8	190.0	118.5	20.5
C-12	C-13	C-2′	C-4′	C-6′
166.8	166.8	157.6	174.8	28.4

Analytical Data

References and Notes

Stankovicova, H.; Fabian, W. M.; Lacova, M. Molecules 1996, 1, 223.
Stankovicova, H.; Gasparova, R.; Lacova, M.; Chovancova, J. Collect. Czech. Chem. Commun. 1997, 62, 781.
Lacova, M.; Stankovicova, H.; Odlerova, Z. Il Pharmaco 1995, 50, 885.
El-Shaaer, H.M.; Perjessy, A.; Zahradnik, P.; Lacova, M.; Matulova, M. Monatsh. Chem 1993, 124, 539.
Lacova, M.; El-Shaaer, H.M.; Loos, D.; Matulova, M.; Chovancova, J.; FurdIk, M. Molecules 1998, 3, 120.
Gasparova, R.; Lacova, M.; El-Shaaer, H.M.; Odlerova, Z. Il Pharmaco 1997, 52, 251.
Lacova, M.; Chovancova, J.; Veverkova, J.; Toma, S. Tetrahedron 1996, 52, 14995.
Nohara, A.; Sugihara, H.; Ukawa, K. Japan. Kokai Tokyo Koho 1978, 78, 111,070. ; Chem. Abstr. 1979, 90, 54828z.
Klutchko, S.; Kaminski, D.; Von Strandtmann, M. U.S. Patent 4,008,252, 1977. ; Chem. Abstr. 1977, 87, 5808a.
Lacova, M.; El-Shaaer, H. M.; Odlerova, Z.; Furdik, M. Chem. Papers 1994, 48, 344.
Deulofeu, V.; Guerrero, T. J. Org. Synth. Coll. 1955, 3, 586.
Coirnwaite, W. R.; Lazarus, S.; Snelling, R. H.; Denoon, C. E. J. Am. Chem. Soc. 1936, 58, 628.
Fitton, A. O.; Frost, J. R.; Suschitsky, H.; Houghton, P. G. Synthesis 1977, 133.
Gasparova, R.; Lacova, M. Collect. Czech. Chem. Commun. 1995, 60, 1178.
Villemin, D.; Martin, B. Synth. Commun. 1995, 25, 3135.
Villemin, D.; Ricard, M. Synth. Commun. 1987, 17, 283.
Nohara, A.; Ishiguto, T.; Sanno, Y. Tetrahedron Lett. 1974, 13, 1183.
Silva, A. M. S.; Silva, A. M. G.; Tome, A. C.; Cavaleiro, J. A. S. J. Org. Chem. 1999, 135.

Samples Availability: Available from the authors and MDPI.

Scheme 1.

Scheme 2.

Table 1. Characterization of the prepared compounds.

**Table 1.** Characterization of the prepared compounds.
Comp.	R	Formula M_r	m.p. °C	w_i (calcd)/ % w_I (found)/ %			Yield %	t_r min
Comp.	R	Formula M_r	m.p. °C	C	H	N	Yield %	t_r min
5a	H	C₁₆H₁₃ N₃ O₄	246 - 248	61.73	4.21	13.50	75	3
		311.29		61.31	4.14	13.41	71	60
5b	CH₃	C₁₇H₁₅ N₃O₄	277 - 279	62.76	4.65	12.92	60	4
		325.32		62.15	4.66	12.59	57	120
5c	Cl	C₁₆H₁₂ClN₃O₄	268 - 270	55.58	3.50	12.15	76	2
		345.74		55.58	3.59	12.13	72	60
5d	Br	C₁₆H₁₂BrN₃O₄	270 - 272	49.25	3.10	10.77	84	1
		390.19		48.91	3.02	10.54	-	-
5e	AcO	C₁₈H₁₅N₃O₆	259 - 262	58.54	4.09	11.38	46	3
		369.33		58.06	4.07	11.28	40	90
5f	NO₂	C₁₆H₁₂N₄O₆	285 - 286	53.94	3.39	15.72	84	3
		356.29		53.83	3.29	15.43	-	-
6a	H	C₁₄H₁₁N₃O₃	250 - 252	62.45	4.12	15.61	70	3
		269.26		62.38	3.96	15.72
6b	CH₃	C₁₅H₁₃N₃O₃	294 - 297	63.60	4.63	14.83	67	3
		283.28		63.24	4.68	14.06
6c	Cl	C₁₄H₁₀ClN₃O₃	356 - 360	55.36	3.32	13.83	92	3
		303.7		55.21	3.49	13.22
6d	Br	C₁₄H₁₀BrN₃O₃	276 - 278	48.30	2.89	12.07	68	3
		348.16		48.25	2.96	12.44
6e	NO₂	C₁₄H₁₀N₄O₅	237 - 240	53.51	3.21	17.83	98	3
		314.26		52.94	2.99	17.39
7a	H	C₁₅H₁₁N₃O₅	253 - 255	57.82	3.51	13.41	69	6
		313.3		57.50	3.90	13.08
7b	Cl	C₁₅H₁₀ClN₃O₅	356 - 360	54.34	3.76	11.18	71	4
		375.76		54.69	3.23	11.23
7c	CH₃	C₁₆H₁₃N₃O₅	299 - 301	58.71	3.97	12.84	58	7
		327.3		58.44	4.30	12.75
7d	Br	C₁₅H₁₀BrN₃O₅	350	45.92	2.55	10.71	60	7
		392.2		46.28	2.36	10.48
8a	H	C₁₃H₈N₂O₃S	292 - 295	57.35	2.96	10.29	79	8
		272.3		56.98	2.91	10.05	72	60
8b	CH₃	C₁₄H₁₀N₂O₃S	315 - 317	58.73	3.52	9.78	70	6
		286.3		58.50	3.52	9.04	66	30
8c	Cl	C₁₃H₇ClN₂O₃S	319 - 321	50.91	2.30	9.13	74	4
		306.7		51.03	2.34	9.05	71	30
8d	Br	C₁₃H₇BrN₂O₃S	329-331	44.46	2.01	7.98	96	9
		351.2		44.53	2.02	7.16	88	60
8e	AcO	C₁₅H₁₀N₂O₅S	303 - 305	54.54	3.05	8.48	62	10
		330.3		53.82	2.98	7.99	59	120
9a	H	C₁₅H₁₁NO₃S₂	215 - 217	56.77	3.49	4.41	70	5
		317.4		57.07	3.48	4.45	74	60
9b	Cl	C₁₅H₁₀ClNO₃S₂	231 - 233	51.21	2.86	3.98	67	5
		351.8		50.96	2.82	3.79	65	60
10a	H	C₁₄H₁₅N₅O₅	325 - 327	55.08	4.95	13.76	0	20
		305.3	decomp.	55.35	4.59	13.65	52	240
10e	OH	C₁₄H₁₅N₃O₆	315 - 317	52.33	4.70	13.08	0	20
		321.3	decomp.	52.12	4.59	12.72	47	260
10f	NO₂	C₁₄H₁₄N₄O₇	>360	48.00	4.02	15.98	0	20
		350.3	decomp.	48.09	3.855	15.77	56	250
11	CH₃	C₁₉H₁₇N₃O₇	221 - 223	57.16	4.25	10.51	0	20 - 30
		399.3		57.10	4.22	10.41	89	15 hr.

^aThe upper yield and reaction time (t_r) data are given for the condensation in microwave oven, the lower data for the classic condensation.

Table 2. ¹H NMR spectra data of prepared compounds.

**Table 2.** ¹H NMR spectra data of prepared compounds.
Compound	Solvent	¹H NMR spectrum δ (ppm)
5a	CDCl₃	2.25 (s, 3H, CH₃); 3.39 (s, 3H, CH₃-N); 6.86 - 8.32 (m, 5H, H-Ar); 9.68 (s, 1H, H-2); 10.84 (s, 1H, NH).
5b	DMSO-d₆	2.50 (s, 3H, CH₃); 2.54(s, 3H, CH₃); 3.57(s, 3H, CH₃-N); 6.56 (s, 1H, H-9); 7.60 - 7.70 (m, 5H, H-Ar); 7.97 (s, 1H, H-5); 9.56 (s, 1H, H-2).
5c	DMSO-d₆	2.76 (s, 3H, CH₃); 3.52 (s, 3H, CH₃-N); 6.72 (s, 1H, H-9); 8.02 (d, 1H, H-8, ³J=9Hz); 8.11 (d, 1H, H-7, ³J=9Hz); 8.32 (d, 1H, H-5, ⁴J=2Hz); 9.54 (s, 1H, H-2).
5d	DMSO-d₆	2.78 (s, 3H, CH₃); 3.53 (s, 3H, CH₃-N); 6.74 (s, 1H, H-9); 7.95 (d, 1H, H-8, ³J=9Hz); 8.24 (d, 1H. H-7, ³J=9Hz); 8.49 (d, 1H, H-5, ⁴J=1.8Hz), 9.55 (s, 1H, H-2).
5e	DMSO-d₆	2.13 (s, 3H, CH₃O); 2.3 (s, 3H, CH₃O); 3.45 (s, 3H, CH₃-N); 6.47 (s, 1H, H-9); 7.6 - 7.85 (m, 3H, H-8, 7, 5); 9.30 (s, 1H, H-2); 11.41 (s (broad), 1H, N-H).
5f	DMSO-d₆	2.13 (s, 3H, CH₃O); 3.21 (s, 3H, CH₃-N); 6.43 (s, 1H, H-9); 8.00(s, 1H, H-8); 8.64 (s, 1H, H-7); 8.85 (s, 1H, H-7); 8.85 (s, 1H, H-5); 9.353 (s, 1H, H-2).
6a	DMSO-d₆	3.35 (s, 3H, CH₃-N); 6.24 (s, 1H, H-9); 7.52 (dd, 1H, H- 7,³J=7.8Hz); 7.69 (dd, 1H, H-8, ³J=7.8Hz); 7.81 (dd, 1H, H-6, ³J=7.8Hz); 8.12 (dd, 1H, H-5, ³J=7.8Hz); 9.88 (s, 1H, H-2); 7.4 - 8.4 (broad, 1H, NH).
6b	DMSO-d₆	2.45 (s, 3H, CH₃); 3.38 (s, 3H, CH₃N); 6.25 (s, 1H, H-9); 7.60 - 7.95 (m, 3H, H-8, 7, 5); 9.86 (s, 1H, H-2); 7.4 - 8.4 (broad, 1H, NH).
7a	DMSO-d₆	3.39 (s, 3H, CH₃CN); 6.19 (s, 1H, H-9); 7.53 (dd, 1H, H-6, ³J=7Hz); 7.69 (d, 1H, H-8, ³J=7Hz); 7.84 (dd, 1H, H-7, ³J=7Hz); 8.12 (d, 1H, H-5, ³J=7Hz); 9.8 (s, 1H, H-2).
7d	DMSO-d₆	3.39 (s, 3H, CH₃CN); 6.19 (s, 1H, H-9); 7.70 (d, 1H, H-8, ³J=8Hz); 7.97 (dd, 1H, H-7, ³J=8Hz, ⁴J=2.2Hz); 8.17 (d, 1H, H-5, ⁴J=2.2Hz); 9.895 (s, 1H, H-2).
7e	DMSO-d₆	3.44 (s, 3H, CH₃-N); 6.59 (s, 1H, H-9); 8.00 (d, 1H, H-8, ³J=9Hz); 8.61 (dd, 1H, H-7, ³J=9Hz, ⁴J=2.5Hz); 8.79 (d, 1H, H-5, ⁴J=2.54Hz); 9.395 (s, 1H, H-2); 9.64 (s( broad), 1H, NH).
8c	DMSO-d₆	6.36 (s, 1H, H - 9); 7.78 (d, 1H, H-8, ³J=10Hz); 7.87 (dd, 1H, H - 7, ³J=10Hz, ⁴J=2.2Hz); 8.23 (d, 1H, ⁴J=2.2Hz); 8.94 (s, 1H, H-5); 11.65 (s, 1H, NH); 12.46 (s, 1H, OH).
8d	DMSO-d₆	6.35 (s, 1H, H - 9); 7.74 (d, 1H, H-8, ³J=8.8Hz); 8.02 (dd, 1H, H - 7, ³J=8.8Hz, ⁴J=2.2Hz); 8.22 (d, 1H, ⁴J=2.2Hz); 8.92 (s, 1H, H-2);
8e	DMSO-d₆	2.33 (s, 3H, CH₃); 6.38 (s, 1H, H - 9); 7.60 (dd, 1H, H-7, ³J=9Hz, ⁴J=1.9Hz); 7.83 (d, 1H, H-8, ³J=9Hz); 7.88 (d, 1H, H-5, ⁴J=1.9Hz); 8.94 (s, 1H, H-2); 11.80 (s, 1H, NH); 12.45 (s, 1H, OH).
9b	DMSO-d₆	2.490 (t, 3H, CH₃); 5.346 (q, 2H, CH₂); 8.84 (s, 1h, H-2); 9.07 (d, 1H, H-8, ³J=9.1Hz); 9.072 (dd, 1H, H-7, ³J=9.1Hz, ⁴J=2Hz); 9.36 (d, 1H, H-5, ⁴J=2Hz); 10.27 (s, 1H, H-9).
10a	DMSO-d₆	6.27 (s, 1H, CH); 7.23 - 7.66 (m, H, Ar - H); 9.25 (s, 1H, CH); 10.26 (b., 6H, NH₂, NH, OH).
10e	DMSO-d₆	3.38 (s, 3H, CH₃); 6.70 (s, 1H, CH); 7.29 - 7.39 (dd, 1H, H-5, J=9Hz); 7.39 - 7.41 (d, 1H, H-3, J=3Hz); 7.57 - 7.60 (d, 1H, H-6, J=9Hz); 9.23 (s, 1H, CH); 10.28 (b., 7H, OH, NH, NH₂).
10f	DMSO-d₆	3.68 (s, 3H, CH₃); 7.95 - 8.81 (m, 3H, Ar-H); 9.32 (s, 1H, CH); 10.00 (b., 6H, OH, NH, NH₂).
11	DMSO-d₆	2.46 (s, 3H, CH₃); 2.48 (s, 3H, CH₃); 4.71 (broad, 5H, NH amide, CO2H, CH); 6.23 - 6.56 (m, 4H, Ar-H, H-2); 7.64 (s, 1H, =CH); 9.47 (s, 1H, NH-imine).

Table 3. IR spectral data of synthesized compounds 5-9.

**Table 3.** IR spectral data of synthesized compounds 5-9.
	ν (cm⁻¹)
Comp.	ν(NH)	ν(C=O)_heterocycl	ν(C=O)_pyrone	ν(C=O)_other
5a	3078 - 3162	1739	1650	1643
5b	3070 - 3175	1740	1650	1642
5c	3075 - 3179	1735	1659	1636
5d	3075 - 3180	1729	1658	1640
5e	3081 - 3181	1739	1652	1630, 1758
5f	3080 - 3177	1745	1660	1641
6a	3070 - 3185	1720	1650
6b	3095 - 3180	1720	1645
6c	3070 - 3175	1735	1655
6d	3090 - 3180	1721	1655
6e	3094 - 3186	1719	1658
7a	3080 - 3230	1719	1657	1740
7b	3075 - 3225	1721	1658	1742
8a	3038 - 3180	1740	1665
8b	3086 - 3185	1739	1668
8c	3070 - 3190	1742	1665
8d	3060 - 3180	1736	1668
8e	3078 - 3185	1745	1663	1750
9a	3069 - 3110	1688	1660
9b	3060 - 3110	1688	1662

Table 4. IR spectral data of synthesized compounds 10 and 11.

**Table 4.** IR spectral data of synthesized compounds 10 and 11.
	ν (cm⁻¹)
Comp.	ν(OH)	ν(NH)	ν(C=O)	ν(C=O)_acid	ν(C=C)
10a	3480-3400	3080-3040	1740	1700	1646
10e	3540-3440	3080-3020	1748	1700	1642
10f	3560-3480	3110-3010	1723	1700	1660
11	3460	3190-3120	1647^a	1720-1722	1620
	-	-	1708^b	-	-

^aν(CO)_pyr, ^bν(CO)_het

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Lacova, M.; Gasparova, R.; Loos, D.; Liptay, T.; Pronayova, N. Effect of Microwave Irradiation on the Condensation of 6-Substituted 3-Formylchromones with Some Five-membered Heterocyclic Compounds. Molecules 2000, 5, 167-178. https://doi.org/10.3390/50200167

AMA Style

Lacova M, Gasparova R, Loos D, Liptay T, Pronayova N. Effect of Microwave Irradiation on the Condensation of 6-Substituted 3-Formylchromones with Some Five-membered Heterocyclic Compounds. Molecules. 2000; 5(2):167-178. https://doi.org/10.3390/50200167

Chicago/Turabian Style

Lacova, Margita, Renata Gasparova, Dusan Loos, Tibor Liptay, and Nada Pronayova. 2000. "Effect of Microwave Irradiation on the Condensation of 6-Substituted 3-Formylchromones with Some Five-membered Heterocyclic Compounds" Molecules 5, no. 2: 167-178. https://doi.org/10.3390/50200167

APA Style

Lacova, M., Gasparova, R., Loos, D., Liptay, T., & Pronayova, N. (2000). Effect of Microwave Irradiation on the Condensation of 6-Substituted 3-Formylchromones with Some Five-membered Heterocyclic Compounds. Molecules, 5(2), 167-178. https://doi.org/10.3390/50200167

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Effect of Microwave Irradiation on the Condensation of 6-Substituted 3-Formylchromones with Some Five-membered Heterocyclic Compounds

Abstract

Introduction

Results and Discussion

Experimental

General

Synthesis of 5a-5f , 8a-8e and 9a, 9b

Method A

Method B

Synthesis of 6a–6e

Method A

Method B

Synthesis of 7a, 7b

Method A

Method B

Acid hydrolysis of compounds 5a, 5e and 5f

Diels - Alder reaction of compound 5b with maleic anhydride (11)

Analytical Data

References and Notes

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