A clay-mediated, regioselective synthesis of 2-(aryl/alkyl)amino-thiazolo[4,5-c]carbazoles

The 3-aminocarbazoles 1a–e were condensed with phenyl and benzyl isothiocyanates on montmorillonite K10 clay or TLC-grade silica gel at room temperature to furnish efficiently the N-phenyl and N-benzylthioureidocarbazoles, 2a–e and 2f, respectively, within minutes. When adsorbed on montmorillonite K10 clay impregnated with para-toluene sulfonic acid (1:1, w/w) and heated at 60–70 °C, 2a–e and 2f furnished the 2-anilino and 2-benzylaminothiazolo[4,5-c]carbazoles, 3a–e and 3f, respectively, regioselectively in high yields. The cyclisation was also effective for the N-methylthioureidocarbazoles 2g–i.