| Abstract
| - Bis(1,3,4-thiadiazolo)-1,3,5-triazinium halides 6 can be easily attacked by nucleophiles at eitherthe C(3a) or the C(4a) position of the central six-membered (cationic) ring. Nucleophilic attackleads to at least two reaction channels, one of which has been previously detected (pathway a) andleads to novel aminals 19. In this paper we report on a second channel (pathway b). Attack ofprimary or secondary amines 8 at C(3a) or C(4a) in 6 (and their analogues 7) leads to the weaklystabilized intermediates 14. A cascade of several proton shifts, ring openings, rearrangements,and ring closure processes is initiated which finally leads via 17 and 18 to novel highly substitutedguanidines 9, 10, 12, and 13. Pathway b seems to be the result of well-balanced negative-hyperconjugative effects in 14 and/or 17 which control the highly selective opening of a relativelystable central 1,3,5-triazinium ring to yield the crucial intermediate 18. Some representatives ofthe guanidines have been characterized by X-ray analyses. Since some of the guanidines containone or two chirality centers, an effort was made to investigate the stereochemistry of thesecompounds.
|
