Microwave assisted synthesis of sydnonyl-

substituted imidazoles

or microwave

Ar'

O O

Ar'

AcOHNH4OAcCN

NO

CO

Ar C

O

H

NC

NH

Ar'Ar'

CN

NO

CO

Ar

3a-6d

1a-d

/

2a-2d

8-10

2a-2c

bezil derivativesR'NH2;7a-7d

CN

NO

CO

ArN

C

Ar'Ar'

N R'

A one-pot condensation of 3-aryl-4-formylsydnones, 1,2-diketones, and ammonium acetate in the presence of acetic acid by classical heating at 90-110 oC for 1-3 days afforded a diverse array of 4,5-diaryl-2-sydnonyl substituted imidazoles.

Such reaction could be completed successfully within several minutes with a microwave irradiation.

2a-2d

/

1a-d 3a-6d

CN

NO

CO

Ar

NC

NH

Ar'Ar'

CN

NO

CO

Ar C

O

H NH4OAc AcOHAr'

O O

Ar'

or microwave+

1a: Ar = C6H5; 1b: Ar = p-CH3C6H4; 1c: Ar = p-CH3OC6H4; 1d: Ar = p-C2H5OC6H4

2a: Ar' = C6H5; 2b: Ar' = p-CH3OC6H4; 2c: Ar' = p-FC6H4; 2d: Ar' = 2-thienyl

Multiwave 3000 was designed by Anton Paar Gmbh. It includes various rotors for fast and complete closed vessel digestion of organic or inorganic samples under high pressure and temperatures.

power: 200w (100w/each ); ramp: 1min pressure: 35 bar; 0.5 bar/sectemperature: 90 oC; hold: 30min

Table 1. Comparision between microwave irradiation (M.W.) and conventional heating in the syntheses of imidazoles 3a-6d

Starting materials 1,2-Diketones Products C. H. Reaction Time

C. H.Yield *(%)

M. W. (100W)Reaction Time

M. W. (100W)Yield *(%)

1a ( Ar = C6H5) 2a 3a 1.5 days 46 45 min 52

1b ( Ar = p-CH3C6H4) 2a 3b 1.5 days 61 45 min 78

1c ( Ar = p-CH3OC6H4) 2a 3c 1.5 days 51 45 min 69

1d ( Ar = p-C2H5OC6H4) 2a 3d 1.5 days 75 45 min 76

1a ( Ar = C6H5) 2b 4a 2 days 58 45 min 70

1b ( Ar = p-CH3C6H4) 2b 4b 2 days 77 45 min 80

1c ( Ar = p-CH3OC6H4) 2b 4c 2 days 64 45 min 74

1d ( Ar = p-C2H5OC6H4) 2b 4d 2 days 67 45 min 75

1a ( Ar = C6H5) 2c 5a 2 days 59 60 min 78

1b ( Ar = p-CH3C6H4) 2c 5b 2 days 72 60 min 85

1c ( Ar = p-CH3OC6H4) 2c 5c 2 days 60 60 min 76

1d ( Ar = p-C2H5OC6H4) 2c 5d 2 days 65 60 min 80

1a ( Ar = C6H5) 2d 6a 3 days 57 90 min 65

1b ( Ar = p-CH3C6H4) 2d 6b 3 days 52 90 min 62

1c ( Ar = p-CH3OC6H4) 2d 6c 3 days 52 90 min 60

1d ( Ar = p-C2H5OC6H4) 2d 6d 3 days 48 90 min 58

4,5-Diaryl-2-sydnonyl-1- substituted imidazoles could also be prepared by one pot condensation of 3-aryl-4-formylsydnones, benzil derivatives, ammonium acetate and 1o amines by the similar treatment.

1d: Ar = p-C2H5OC6H4; 2a: Ar' = C6H5; 2b: Ar' = p-CH3OC6H4; 2c: Ar' = p-FC6H4

7a: R' = iso-butyl; 7b: R' = C6H5CH2CH2; 7c: R' = C6H5CH2; 7d: R' = CH3(CH2)5

+

2a-2c

/

1d

CN

NO

CO

Ar C

O

H NH4OAc AcOHAr'

O O

Ar'

or microwave+

8-10

R'NH2 CN

NO

CO

ArN

C

Ar'Ar'

N R'

7a-7d

Table 2. Comparision between microwave irradiation (M.W.) and

conventional heating in the syntheses of imidazoles (8a-10a)

1,2-Diketones Amines Products C. H. Reaction Time

C. H.Yield *(%)

M. W. (100W)Reaction Time

M. W. (100W)Yield *(%)

2a 7a (R' = iso-butyl) 8a 3 days 34 3 hr 56

2a 7b (R' = C6H5CH2CH2) 8b 2 days 25 2 hr 47

2a 7c (R' = C6H5CH2) 8c 2 days 20 2 hr 46

2a 7d (R' = CH3(CH2)5) 8d 2 days 22 2 hr 50

2b 7a (R' = iso-butyl) 9a 3 days 20 3 hr 45

2b 7b (R' = C6H5CH2CH2) 9b 2 days 34 2 hr 60

2b 7c (R' = C6H5CH2) 9c 2 days 26 2 hr 55

2c 7a (R' = iso-butyl) 10a 3 days 28 3 hr 56

Figure 1. ORTEP drawing of compound 3-(4-ethoxyphenyl)-4- (1-

isobutyl-4,5-diphenyl-1H-imidazol-2-yl)sydnone (8a).

Figure 2. ORTEP drawing of compound 3-(4-ethoxyphenyl) -4-(1- phenethyl-4,5-diphenyl-1H-imidazol-2-yl)sydnone (8b).

Figure 3. ORTEP drawing of compound 4-(1-benzyl-4,5-diphenyl – 1H-imidazol-2-yl)-3-(4-ethoxyphenyl)sydnone (8c).

Figure 4. ORTEP drawing of compound 4-[4,5-Bis-(4-fluorophenyl)-1- isobutyl-1H-imidazol-2-yl]-3-(4-ethoxyphenyl)sydnone (10a).