microwave assisted synthesis of sydnonyl- substituted imidazoles
TRANSCRIPT
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).