Aminodemethylthiolation of 3-Methylthio-l,2,4-Triazines

4-Triazines and Benzo-1,2,4-Triazines a. Aminodemethylthiolation of 3-Methylthio-l,2,4-Triazines 

The reaction of 3-(methylthio)-5-i -l,2,4-triazine with potassium amide/liquid ammonia was the first example in 1,2,4-triazine chemistry where the replacement of the methylthio group by an amino group was found to occur with important participation of the Sn(ANRORC) mechanism (75RTC204). This was proved by the experiment that the 3-amino- 

ANRORC process, i.e., adduct formation at C-5, is not prevented by these groups. This is a remarkable effect, certainly when taking into consideration the bulkiness of the r-butyl group, which could be expected to diminish the participation of the ANRORC process. It demonstrates that the 

When the reaction was studied with the N-labeled 3-X-5-phenyl-[4- N]-l,2,4-triazine X = Cl, Br) as substrate, it was established by the same methodology as described for the aminodemethylthiolation (see Section 

3-Fluoro-5-phenyl-l,2,4-triazine (109, X = F) reacts much faster than the 3-chloro-, 3-bromo-, or 3-iodo-compound. Moreover, the reaction mixture obtained is cleaner than that from the corresponding 3-chloro- or 3-bromo compounds 3-amino-5-phenyl-l,2,4-triazine (110) is formed in good yield. This conversion takes place to only a small extent (18%) via the ANRORC process the main part of the aminodefluorination seems to involve the Sn(AE) mechanism. This result is consistent with the observation that the aminodefluorination of 4,6-diphenyl-2-fluoropyrimidine follows the Sn(AE) process, whereas 2-fluoro-4-phenylpyrimidine (position 6 is vacant for addition of the nucleophile) reacts for the most part according to the Sn(ANRORC) mechanism (see Section II,C,l,c). 

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