Syntheses of a novel class of 5/6/5-heterocycles: Convenient routes from aldehydes to bis(1,3,4-thiadiazolo)-1,3,5-triazinium halides

Novel 5/6/5 heterocycles, 1,3,4-thiadiazolo[3,2-a]-1,3,4-thiadiazolo [3,2-d ]-1,3,5-triazinium halides 7, have been synthesized by the reaction of 2-am ino-1,3,4-thiadiazoles 6 with either 1-(haloalkyl)pyridinium halides 4 or N ,N'-methylenebis(pyridinium) dibromides 5. The tricyclic compounds 7 are ge nerated in the course of several successive reaction steps in which specifi c proton migrations, bond-breaking and bond-forming processes occur. The st ructures 7 have been verified by spectral data (H-1 and C-13 NMR, MS), X-ra y analysis and ab initio calculations. The latter show that both sp(2)-C at oms C(10) and C(12) of 7 are significantly positively charged and, therefor e, exhibit electrophilic properties towards the primary amino group of the amino-thiadiazoles 6. In the course of a multi-step reaction cascade of the 6/7 mixture, novel multi-aza/thia heterocycles 8 are formed. The structure s of the latter compounds have been confirmed by X-ray analysis as well as by detailed experimental and theoretical NMR-spectroscopic studies.