Efficient synthesis of novel cyclic fused-phenothiazines via domino cyclization of 2-(benzo[b][1,4]thiazin-3-ylidene)acetate, aromatic aldehydes and cyclic 1,3-diketones

Abstract

Functionalized 2,3,4,7-tetrahydrobenzo[c]phenothiazines and 7,9,10,12-tetrahydrobenzo[b]phenothiazines were selectively synthesized from a three-component reaction of aromatic aldehydes, cyclic 1,3-diketones and methyl 2-(benzo[b][1,4]thiazin-3-ylidene)acetate in refluxing AcOH/CH₃CN medium or in refluxing acetic acid. On the other hand, the domino cyclization reaction of aromatic aldehydes with methyl 2-(benzo[b][1,4]thiazin-3-ylidene)acetate in AcOH/CH₃CN medium resulted in polycyclic 8,14-methanobenzo[2,3][1,4]thiazocino[6,7-a]phenothiazines in satisfactory yields. Additionally, similar reactions with some typical 1,2-dicarbonyl compounds afforded diverse polycyclic compounds.