Microwave‐assisted Cadogan reaction for the synthesis of 2‐aryl‐2H‐indazoles, 2‐aryl‐1H‐benzimidazoles, 2‐carbonylindoles, carbazole, and phenazine

Abstract

The Cadogan reaction, a widely accepted route for the synthesis of nitrogen containing heterocycles, is modified by using microwave radiation as the source of heat instead of the conventional heating by reflux in a nitrogen atmosphere for several hours. Appropriate starting materials were mixed with triethyl phosphite or triphenylphosphine and irradiated with microwaves for several minutes at a specific power to give the desired products. The indazoles were prepared by irradiating N‐(2‐nitrobenzylidene) anilines with triethyl phosphite at 200 W for 12–14 min to give 85–92% product yields. Irradiation of the mixture of N‐benzylidene‐2‐nitroanilines and triphenylphosphine at 200 W for 3–5 min yielded 93–96% of the benzimidazoles. The carbonylindoles were obtained in 61–68% yields by irradiating 2‐nitrochalcone or alkyl 2‐nitrocinnamates and triphenylphosphine with microwaves at 80–200 W for 8–11 min. The mixture of 2‐nitrobiphenyl and triphenylphosphine yielded 96% of carbazole when irradiated with microwaves at 200 W for 2 min while 75% of phenazine was obtained by irradiating the mixture of 2‐nitrodiphenylamine and triphenylphosphine with microwaves at 200 W for 3.5 min. These results show that microwave‐assisted Cadogan reactions gave better product yields at shorter reaction times. J. Heterocyclic Chem., (2009).

Metal Acetylacetonates Covalently Anchored onto Amine Functionalized Silica/Starch Composite for the One-Pot Thioetherification and Synthesis of 2H-Indazoles

“…Thionyl chloride was added drop-wise over a period of 15 min at room temperature followed by stirring for 10 h at 80°C. The untreated SOCl 2 was removed by distillation and the resulting silica chloride was vacuum dried at 90°C [42]. Silica/starch composite was prepared by refluxing mixture of silica chloride (5 g), corn starch (2 g), and triethyl amine (0.5 mL) in CHCl 3 (30 mL) for 10 h. The reaction mixture was filtered, washed with chloroform (3 9 10 mL) and water (3 9 20 mL) followed by drying in the oven at 120°C for 2 h. To silica/starch composite (5 g) in dry toluene (100 mL), 3-aminopropyl(trimethoxy) silane (0.89 g, 5 mmol) was added and the reaction mixture was refluxed for 12 h. The 3-aminopropylsilica/starch substrate was filtered off, washed with hot toluene (50 mL) and dried at 110°C for 5 h to get the surface bound amino groups.…”

Synthetic Approaches to 2-Arylbenzimidazoles: A Review

“…In addition 2-arylbenzimidazoles were also synthesized by replacing aryl acids with aryl chlorides [60][61][62][63][64][65][66][67][68][69][70][71]. Efficient one-pot syntheses of 2-arylbenzimidazoles starting from 2-nitroaniline have been also reported [191][192][193][194][195][196]. A large number of reagents with different combination of solvents under different reaction conditions were explored from time to time in order to find an economical and efficient method for the synthesis of 2-arylbenzimidazoles.…”

High thermal-stability benzocarbazole derivatives as bipolar host materials for phosphorescent organic light-emitting diodes

“…Here, two key intermediate compounds 9-(dibenzo [b,d]thiophen-4-yl)-7H-benzo[c] carbazole (1e3) and 5-(dibenzo[b,d]thiophen-4-yl)-7H-benzo[c]carbazole (2e4) were prepared through multiple steps according to the methods reported in the litertures [22,23]. Subsequently, the desired products (DYNS and DYSN) were obtained by the palladium catalyzed BuchwaldeHartwig cross coupling reaction of benzocarbazole species (1e3 and 2e4) and bromide intermediate 2-(4-bromophenyl)-1-phenyl-1H-benzo[d]imidazole in 60% yield.…”

“…The solvent was removed in vacuum and the crude product was purified by SiO 2 column chromatography, affording a white solid (0.10 g, 60%). IR (KBr, disk) n 3051 22,. 1602.70, 1586.50, 1450.61, 1434.95, 744.64, 699.88 cm À1 .…”