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-amwinothiazole with aqueous formaldehyde in water at 0-5 degrees 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 degrees 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.