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

R. Gasparová, M. Lácová* and D. Loos*

Department of Organic Chemistry, Faculty of Natural Sciences, Comenius University, Mlynská dolina CH-2, SK-842 15 Bratislava, Slovak Republic, Tel. +421 7 60296338, Fax +421 7 65429064, E-mail: lacova@fns.uniba.sk and loos@fns.uniba.sk

Introduction
This study is continuation of our earlier works [1 - 4] in which we described theoretical, spectral and biological properties of the new synthesized chromone and chromanone derivatives. In the some of our last papers [5 - 7] we interested in condensation reactions realized under focused microwave irradiation in microwave oven.
The aim of this study was the preparation of some new five-membered-nitrogen heterocyclic derivatives of chromone. These analogs could be valuable for using as intermediates and as well as available by condensation reaction. 3-Formylchromones I were chosen as synthetically versatile molecules with reactive carbonyl group. They have a considerable significance not only for their biological activities [8 - 10] but also for their reactivity towards nucleophiles what enables the synthesis of a wide variety of heterocycles. The next goal of this paper was the study of condensation of 3-formylchromones Ia - If with active methylene groups of 2-amino-1-methylimidazolidin-4-one (creatinine) II, 2-thioxoimidazolidin-4-one (thiohydantoin) III and 3-ethyl-2-thioxothiazolidin-4-one (3-ethylrhodanine) IV, respectively, in condition of microwave irradiation and for comparison using standard method at various experimental conditions.
Five-membered ring heterocycles II - IV like creatinine, thiohydantoin or rhodanine derivatives known as precursors of [alpha]-amino acids, can be condensed easily with aldehydes. Condensations of creatinine with aldehydes [11, 12] as well as the Gränacher synthesis of rhodanine with 3-formylchromone [13] under "classical" conditions last at high temperatures several hours at high temperatures (160 - 180 °C).
As we have shown before [14], the microwave irradiation is a suitable method for condensations of 3-formylchromones with active methylene compounds. Condensations of creatinine [15] and thiohydantoin [16] with aldehydes described by Villemin and al. took place without a solvent under microwave irradiation in good yields.
The starting 3-formylchromones used in this work are accessible via Vilsmeier - double formylation of appropriate o-hydroxyacetophenones [17]. Commercial preparation of nitrogen heterocycles were used for reactions. The reaction processes are outlined in scheme 1, 2 and 3. The details of the experimental results are listed in Table 6.


===================================================================
* Experimental
* Schemes
* Tables
* Results and discussion
* Summary
* References
* Acknowledgment
Experimental
Products were determined by elemental analyses (Table 1), IR spectra (Table 2) and NMR -spectra (Table 3).
The melting points were determined on Kofler block and are uncorrected. Infrared spectra were recorded on a Specord IR 75 spectrometer (Zeiss Jena) in 400 - 4000 cm-1 region in nujol suspension.
Proton NMR spectrum was measured on 300 MHz spectrometer VARIAN GEMINI 2000 in deuterium DMSO at 50 - 80 OC.
All microwave assisted reactions were carried out in a Lavis - 1000 multi Quant microwave oven. The apparaturs has been adapted for laboratory application with magnetic stirring and an external reflux condenser.
Synthesis of Va - Vf , VIIIa - VIIIe and IXa, IXb
Method A.
A mixture of 6-R-3-formylchromone Ia - If (2.87 mmol), creatinine II (or thiohydantoin III, 3-ethyrhodanine IV) ( 2.87 mmol) in 2 cm3 dry acetic anhydride in the presence freshly fused potassium acetate was stirred and irradiated in microwave oven over a period, given in Table 1. The solid was filtered off. Products Va -Vf and VIIIa - IXb were recrystallized from dioxane.
Method B.
A mixture of the same composition as in method A was heated at 110 -120 °C over a period, given in Table 1. Isolation of products was identical as in method A
Synthesis of VIa -VIe
Method A
Mixture of 6-R-3-formylchromone I (2.87 mmol), creatinine II (2.87 mmol), catalytic amount of H3BO3 (20 mg) was heated in 1cm3 of dry dimethyl sulfoxide over 3 h. The solid product was filtered off and recrystallized from dioxane.
Method B
A mixture of the same composition as in method A was , stirred and irradiated at 270 W in microwave oven.
Synthesis of VIIa, VIIb
Method A
Creatinine II (2.87 mmol) was dissolved in 1 cm3 dry dimethylformamide and ethyl chloroformate was added to the solution. Mixture was stirred at room temperature over 3 h. Then 6-R-3-formylchromone I (2.87 mmol) was added to mixture and heated at 90 °C over 6 h. Solid product was filtered off and recrystallized from dioxane.
Method B
The same mixtureas used in procedure A was irradiated in microwave oven at 270 W. The isolation of products is the same as above.
The acid hydrolysis of compounds Va, Ve and Vf
The solution of 0.3 g (1 mmol) creatinine derivate Va (or Ve, Vf) in 10 ml of concentrated hydrochlorid acid was heated at 90 - 100 oC for 4 hrs. After cooling the resulting white crystals were filtered off, washed with cold water and recrystallized from dioxan. Compounds Xa, Xe and Xf were prepared.
13C NMR spectral data for compound Xe.
13C NMR [delta](ppm) (DMSO - d6, 300MHz)
155.45(C-1 ) 123.77(C-2 ) 123.65(C-3 ) 154.87(C-4 ) 107.95(C-5 ) 120.11(C-6 ) 174.53(C-7 )
114.78(C-8 ) 157.60(C-9 ) 109.79(C-10) 130.04(C-11) 163.32(C-12) 28.69(C-13) 149.23(C-14)
Diels - Alder reaction of compound Vb with maleinanhydride
The mixture of 1g (2.51 mmol) compound Vb with and 0.52 g (5.02 mmol) maleinanhydride in 3 ml toluene was heated at 40 oC over 15 hrs. The solid aduct was filtered off, washed by 10 ml toluene and dried up. Then the product suspension in 30 ml water was stirred at 40 oC over 3 hrs. The solid acid was removed by suction and recrystalized from ethanole. Yield 64 %.

Scheme 1



Scheme 2


Scheme 3

Table 1. Characterization of the prepared compounds.

Compound

R

Formula

m.p.

wi (calcd)/ %

wI (found)/ %

Yield

tr



Mr

°C

C

H

N

%

min

Va

H

C16H13N3O4

246 - 248

61.73

4.21

13.50

75

3



311.29


61.31

4.14

13.41

71

60

Vb

CH3

C17H15N3O4

277 - 279

62.76

4.65

12.92

60

4



325.32


62.15

4.66

12.59

57

120

Vc

Cl

C16H12ClN3O4

268 - 270

55.58

3.50

12.15

76

2



345.74


55.58

3.59

12.13

72

60

Vd

Br

C16H12BrN3O4

270 - 272

49.25

3.10

10.77

84

1



390.19


48.91

3.02

10.54

-

-

Ve

AcO

C18H15N3O6

259 - 262

58.54

4.09

11.38

46

3



369.33


58.06

4.07

11.28

40

90

Vf

NO2

C16H12N4O6

285 - 286

53.94

3.39

15.72

84

3



356.29


53.83

3.29

15.43

-

-

VIa

H

C14H11N3O3

250 - 252

62.45

4.12

15.61

70

3



269.26


62.38

3.96

15.72


VIb

CH3

C15H13N3O3

294 - 297

63.60

4.63

14.83

67

3



283.28


63.24

4.68

14.06



VIc

Cl

C14H10ClN3O3

356 - 360

55.36

3.32

13.83

92

3



303.7


55.21

3.49

13.22



VId

Br

C14H10BrN3O3

276 - 278

48.30

2.89

12.07

68

3



348.16


48.25

2.96

12.44



VIe

NO2

C14H10N4O5

237 - 240

53.51

3.21

17.83

98

3



314.26


52.94

2.99

17.39



VIIa

H

C15H11N3O5

253 - 255

57.82

3.51

13.41

69

6



313.3


57.50

3.90

13.08


VIIb

Cl

C15H10ClN3O5

356 - 360

54.34

3.76

11.18

71

4



375.76


54.69

3.23

11.23




Table 1. Continued.

Compound

R

Formula

m.p.

wi (calcd)/ %

wI (found)/ %

Yield

tr



Mr

°C

C

H

N

%

min

VIIc

CH3

C16H13N3O5

299 - 301

58.71

3.97

12.84

58

7



327.3


58.44

4.30

12.75



VIId

Br

C15H10BrN3O5

350

45.92

2.55

10.71

60

7



392.2


46.28

2.36

10.48



VIIe

NO2

C15H10N4O7

320 - 321

50.25

2.79

15.63

60

2



358.2


49.92

4.09

15.78



VIIIa

H

C13H8N2O3S

292 - 295

57.35

2.96

10.29

79

8



272.3


56.98

2.91

10.05

72

60

VIIIb

CH3

C14H10N2O3S

315 - 317

58.73

3.52

9.78

70

6



286.3


58.50

3.52

9.04

66

30

VIIIc

Cl

C13H7ClN2O3S

319 - 321

50.91

2.30

9.13

74

4



306.7


51.03

2.34

9.05

71

30

VIIId

Br

C13H7BrN2O3S

329 - 331

44.46

2.01

7.98

96

9



351.2


44.53

2.02

7.16

88

60

VIIIe

AcO

C15H10N2O5S

303 - 305

54.54

3.05

8.48

62

10



330.3


53.82

2.98

7.99

59

120

IXa

H

C15H11NO3S2

215 - 217

56.77

3.49

4.41

70

5



317.4


57.07

3.48

4.45

74

60

IXb

Cl

C15H10ClNO3S2

231 - 233

51.21

2.86

3.98

67

5



351.8


50.96

2.82

3.79

65

60

Xa

H

C14H15N5O5

325 - 327

55.08

4.95

13.76

52




305.3

decomp.

55.35

4.59

13.65



Xe

OH

C14H15N3O6

315 - 317

52.33

4.70

13.08

47




321.3

decomp.

52.12

4.59

12.72



Xf

NO2

C14H14N4O7

>360

48.00

4.02

15.98

56




350.3

decomp.

48.09

3.855

15.77



* The upper data of yield and reaction time (tr) are given for the condensation in microwave oven, the lower data for the classic condensation.
Table 2. IR Spectral Data of Synthesized Compounds


[nu]/cm-1

Compoud

[nu](NH)

[nu](C=O)heterocycl.

[nu](C=O)pyrone

[nu](C=O)other

Va

3078 - 3162

1739

1650

1643

Vb

3070 - 3175

1740

1650

1642

Vc

3075 - 3179

1735

1659

1636

Vd

3075 - 3180

1729

1658

1640

Ve

3081 - 3181

1739

1652

1630, 1758

Vf

3080 - 3177

1745

1660

1641

VIa

3070 - 3185

1720

1650


VIb

3095 - 3180

1720

1645


VIc

3070 - 3175

1735

1655


VId

3090 - 3180

1721

1655


VIe

3094 - 3186

1719

1658


VIIa

3080 - 3230

1719

1657

1740

VIIb

3075 - 3225

1721

1658

1742

VIIIa

3038 - 3180

1740

1665


VIIIb

3086 - 3185

1739

1668


VIIIc

3070 - 3190

1742

1665


VIIId

3060 - 3180

1736

1668


VIIIe

3078 - 3185

1745

1663

1750

IXa

3069 - 3110

1688

1660


IXb

3060 - 3110

1688

1662



Table 2 Continued


[nu]/cm-1





Compound

[nu](OH)

[nu](NH)

[nu](C0)

[nu](CO)acid

[nu](C=C)

Xa

3480-3400

3080-3040

1740

1700

1646

Xe

3540-3440

3080-3020

1748

1700

1642

Xf

3560-3480

3110-3010

1723

1700

1660

XI

3460

3190-3120

1647a

1720-1722

1620


-

-

1708b

-

-

a[nu](CO)pyr, b[nu](CO)het
Table 3. 1H NMR spectra data of prepared compounds

Compound

Solvent

1H NMR spectrum [delta] (ppm)

Va

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).

Vb

DMSO

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).

Vc

DMSO

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).

Vd

DMSO

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).

Ve

DMSO

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).

Vf

DMSO

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).

VIa

DMSO

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).


Table 3. Continued

Compound

Solvent

1H NMR spectrum [delta] (ppm)

VIb

DMSO

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).

VIIa

DMSO

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).

VIId

DMSO

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).

VIIe

DMSO

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).

VIIIc

DMSO

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).

VIIId

DMSO

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);




VIIIe

DMSO

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).


Table 3. Continued

Compound

Solvent

1H NMR spectrum [delta] (ppm)

IXb

DMSO

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).

Xa

DMSO

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).

Xe

DMSO

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).

Xf

DMSO

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).

XI

DMSO

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).


Results and Discussion
2-Acetamido-1-methyl-5-[(6-R-4-oxo-4H-benzopyran-3-yl)methylidene]-4,5-dihydroimidazol-4-ones Va - Vf were obtained by condensations of Ia - If with creatinine II were carried out in acetic anhydride, both under classical and microwave irradiation conditions.
Although the yields in both methods were almost the same (46 - 84 %), reactions in microwave oven were considerably shorter (Table 1).
When boric acid instead of potassium acetate was used as a catalyst and reaction was carried out in dimethyl sulfoxide, 2-imino-1-methyl-5-[(6-R-4-oxo-4H-[1]-benzopyran-3-yl) methylidene]imidazolidin-4-ones VIa - VIe were obtained in 67 - 98 % yields.
A convenient synthesis of 1-metyl-4-oxo-5-[(6-R-4-oxo-4H-[1]-benzopyran-3-yl)methylidene]-4,5-dihydroimidazol-2-carbamoic acids VII was realized by reaction of creatinine II with ethylchloroformate in N, N - dimethylformamide with subsequent addition of aldehyde I. The hydrolyzed products VIIa - VIIe with 69 - 71 % yields were obtained by both classical and microwave irradiation methods, respectively. Compounds VII resulted from utilization of condensing water in the process of hydrolysis, because carbamoic acids VII have been created in all our experiments, also in case of anhydrous conditions. In the 1H NMR spectra of compounds VII did not occur signals for ethyloxygroup.
Condensations of I with thiohydantoin III were carried out in acetic anhydride in the presence of potassium acetate. The difference of reaction times between these two condensation methods was also evident although the yields of 2-thioxo-5-[(6-R-4-oxo-4H-[1]-benzopyran-3-yl) methylidene]imidazolidin-4-ones VIIIa -VIIIe were comparable (59 - 96%).
Reactions of I with 3-ethylrhodanine IV in microwave oven lead to arising of 2-thioxo-5-[(6-R-4-oxo-4H-benzopyran-3-yl)methylidene]thiazolidin-4-ones IXa and IXb in 67 - 70 % yields.
All condensation products are stable solid compounds, rather insoluble in common solvents, with high melting points. For their difficult solubility in DMSO we had to make their 1H NMR spectra measured at elevated temperature.
We tried to hydrolyze some of prepared compounds in diluted mineral acids, but use of concentrated hydrochloric acid was successful only by case of 4 hrs. reflux. Thus were isolated compounds X with both opened heterocycles (yields 47 - 56 %). On the base of 1H NMR -, 13C NMR - spectra and elemental analysis we could propose the structure of compounds X, which contain guanidinyl, carboxyl and enolic groups. Compounds X can be regarded as a mixtures of isomers with a very fast tautomeric equilibrium both enolic and oxo groups. The assumption of fast tautomeric equilibrium is supported by the high data for shift signals of C-9 in 13C NMR spectra.
We attempted to realize Diels - Alder reactions with various dienophiles, using e.g. maleinanhydride, diethyl butindioate and tetracyanoethylene classic as well as microwave irradiation - focused procedures. Only heating a mixture of Vb in toluene with surplus of maleinanhydride at 40 oC over 15 hrs. was successful and was formed out spiroheterocyclic aducts XI (yield 64 %). The using of microwave irradiation for Diels - Alder experiments was unsuccessful.
Summary
The synthesis of different types of 3-substituted 4H-4-oxobenzopyranes was realized under focused microwave irradiation as well as by a classic method.
The beneficial effect of microwave irradiation on aldol condensation of 3-formylchromones with 2-imino-1-methylimidazolidine-4-one (creatine), 2-thioxoimidazolidine-4-one (thiohydantoin) and 2-etyl-2-thioxothiazolidin-4-one (3-ethylrodanine) in different reaction media is described. Our results showed that the effect of microwave irradiation on studied reactions caused the shortening of reaction time, smoothly increased the yields. The subsequent product reaction with some nucleophiles are discussed. The structures of products has been prooved by elemental analysis, IR - and 1H NMR - spectra.
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Acknowledgments. The authors' thanks are due to Dr. K. Gáplovská for elemental analyses. Mgr. I. Prokes for measurement of proton NMR spectra and Dr. A. Perjéssy for IR spectra measurement, members of Faculty of Natural Sciences, Comenius University, Bratislava. Financial support for this research by the Slovak Grant Agency is gratefully acknowledged, Grant No. 1/5085/98.