Microwave-Assisted Cadogan Reaction for the Synthesis of 2-Aryl-2H-indazoles, 2-Aryl-1H-benzimidazoles, 2-Carbonylindoles, Carbazole, and Phenazine

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...

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Published inJournal of heterocyclic chemistry Vol. 46; no. 6; pp. 1309 - 1317
Main Authors Cuevas Creencia, Evelyn, Kosaka, Masahiro, Muramatsu, Toshikatsu, Kobayashi, Masashi, Iizuka, Tomohiro, Horaguchi, Takaaki
Format Journal Article
LanguageEnglish
Published HOBOKEN Wiley 01.11.2009
Subjects
Chemistry
Chemistry, Organic
Physical Sciences
Science & Technology
TRIETHYL PHOSPHITE
ORGANIC-SYNTHESIS
CYCLIZATION REACTIONS
ONE-POT
TERVALENT PHOSPHORUS REAGENTS
CYCLISATION REACTION
NITROSO-COMPOUNDS
ORGANOPHOSPHORUS COMPOUNDS
DERIVATIVES
HETEROCYCLIC-COMPOUNDS
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Summary: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.
ISSN:0022-152X
1943-5193
DOI:10.1002/jhet.267