Control of the reaction between 2-aminobenzothiazoles and Mannich bases. Synthesis of pyrido[2,1-b][1,3]benzothiazoles versus [1,3]benzothiazolo[2,3-b]quinazolines

摘要

Reactions between 2-aminobenzothiazoles and Mannich bases are observed to be selectively controlled by thensteric hindrance in the latter. Pyrido[2,1-b][1,3]benzothiazoles 3 are produced with non-sterically hindered Mannichnbases such as 3-(dimethylamino)propiophenone hydrochlorides 2, whilst [1,3]benzothiazolo[2,3-b]quinazolines arenproduced with bulky Mannich bases such as 2-(dimethylaminomethyl)tetralone 4. This is shown by reactions withn2-amino-5-(ethylsulfanyl)thiadiazole, which was previously reported to follow the former reaction pathway with 2,nwhile the reaction with 4 follows the latter reaction pathway. The final structures are established by NMR andnX-ray diffraction, thus confirming the cyclization processes.