1,3,4-THIADIAZOLES. REGIOSELECTIVE <i>O</i>-DEMETHYLATION ON DEHYDRATIVE CYCLIZATION OF 1-(3,4,5-TRIMETHOXYBENZOYL)4-SUBSTITUTED THIOSEMICARBAZIDES WITH SULPHURIC ACID
作者:Mohamed Al-Omar、Omar A. Al-Deeb、Hamad A. Al-Khamees、Ali A. El-Emam
DOI:10.1080/10426500490485525
日期:2004.12.1
Cyclization of 1-(3,4,5-trimethoxybenzoyl)-4-substituted thiosemicarbazides 2a-g with sulphuric acid at ambient temperature afforded the selectively demethylated products 2-(4-hydroxy-3,5-dimethoxyphenyl)5-substituted amino-1,3,4-thiodiazoles 4a-g. Meanwhile, dehydrative cyclization of 1-(3,4,5-trimethoxybenzoyl)-4-(benzyl or t-butyl)thiosemicarbazides 2h,i with sulphuric acid yielded 2-(4-hydroxy-3,5-dimethoxyphenyl)-5-amino-1,3,4-thiadiazole 5. On the other hand, dehydration of 2h,i by heating with phosphorus oxychloride yielded 2-(3,4,5-trimethoxyphenyl)-5-amino-1,3,4-thiadiazole 6.