Evidences of some unusual behaviours of 2‐aminothiazol and 2‐aminobenzothiazol in reactions with formaldehyde and glyoxal

In contrast to the previously reported acid‐catalyzed reaction of 2‐aminothiazole with aqueous formaldehyde in water at 0‐5 °C which afforded N,N ′‐bis(2‐thiazolyl)methanediamine ( 4 ), 5,5′‐methylenebis(2‐aminothiazole) ( 5 ) is obtained as the unique product under reflux conditions. Reaction of 2‐aminobenzothiazole with aqueous formaldehyde in acetonitrile at 0‐5 °C or under reflux conditions produces (2‐benzothiazolylamino)methanol ( 6 ) or N,N ′‐bis(2‐benzothiazolyl)methanediamine ( 7 ), respectively. Heating monoamine 6 in acetonitrile remarkably yields the symmetric diamine 7 . While cyclocondensation of 2‐aminothiazole with aqueous glyoxal in acetonitrile gives 3,4,8,9‐tetrahydroxy‐7,10‐bis(2‐thiazolyl)‐2,5‐dioxa‐7,10‐diazabicyclo[4.4.0]decane ( 8 ), reaction of 2‐aminobenzothiazole with glyoxal fails to produce similar results; In the presence of aqueous formaldehyde, although the former reaction leads to the formation of 4‐hydroxy‐5‐(thiazolylamino)‐1,3‐bis(2‐thiazolyl)imidazolidine ( 9 ), utilization of 2‐aminobenzothiazole gives 4,5‐dihydroxy‐1,3‐bis(2‐benzothiazolyl)imidazolidine ( 10 ). Condensation of either 6 or 7 with aqueous glyoxal affords compound 10 . Details of the reactions will be discussed in this presentation.