Synthesis and Antioxidant Evaluation of Some New 3‐Substituted Coumarins

3‐Acetylcoumarin ( 1 ) was utilized as a key intermediate for the synthesis of 2‐aminothiazole derivative 3 via bromination of 1 to afford acetylbromide 2 followed by treatment with thiourea or via Biginelli reaction of 1 . Treatment of 3 with 5‐chloro‐3‐methyl‐1‐phenyl‐1 H ‐pyrazole‐4‐carbaldehyde, 2‐methyl‐4 H ‐benzo[ d ][1,3]oxazin‐4‐one, furo[3,4‐ b ]pyrazine‐5,7‐dione or 2‐methyl‐5,6,7,8‐tetrahydro‐4 H ‐benzothieno[2,3‐ d ][1,3]oxazin‐4‐one afforded diazine derivatives 4–7 . Also, pyridopyrimidine 8 was obtained via a one pot reaction of 6‐aminothiouracil, p ‐chlorobenzaldehyde and 3‐acetylcoumarin. Moreover, refluxing of 6‐aminothiouracil with one equivalent amount of 2 afforded the thiazolopyrimidine 9 , while the pyrrolothiazolopyrimidine 10 was revealed when two equivalent amounts of 2 was used. Furthermore, treatment of enamine 11 with 2‐aminobenzothiazole or 6‐aminothiouracil afforded the pyrimidine derivatives 12 and 13 , respectively. Transamination of enamine 11 with m ‐anisidine followed by cyclization of the resulting enaminone 14 gave the desired quinoline 15 . Also, treatment of 11 with thiophenol in dioxane gave the mercapto derivative 16 . Moreover, coupling of 11 with 4,6‐dimethyl‐1 H ‐pyrazolo[3,4‐ b ]pyridin‐3‐yl‐diazonium chloride, followed by complete cyclization of the resulting product afforded the pyridopyrazolothiazine 19 via the intermediate 18 . Furthermore, the pyrazolopyrimidine 20 was revealed via a one pot condensation of 11 , 3‐methyl‐1‐phenyl‐1 H ‐pyrazol‐5(4 H )‐one and ammonium acetate. The thiadiazine derivatives 21–23 were obtained via treatment of 2 with the corresponding o ‐aminothiols. Desulphonation of 23 afforded the pyrazolotriazine 24 . Finally, reaction of 2 with 2‐hydroxybenzaldehyde gave benzofuran derivative 25 . Representative compounds of the synthesized products were evaluated as antioxidant agents.