Nucleophilic substitution, ANRORC 1,2,4-triazines

The amination of 2.4-diphenyl-1,3,5-triazine (7, X = H) with potassium amide in anhydrous liquid ammonia at -33°C occurs by a Chichibabin-type reaction, i.e. replacement of H" by NH via nucleophilic substitution involving an addition-elimination process (SsAE). In contrast, the 2-methylsulfanyl derivative 7 (X = SMe) is aminated nearly exclusively by a ringopening-ring-closing sequence [Sn(ANRORC)].52... 

Ring-degenerate transformations initiated by the nucleophilic addition at C-5 of the 1,2,4-triazine ring have also been reported to occur in reactions of 4-aryl-substituted 3-methylthio-l,2,4-triazine-3,5-diones with hydrazine hydrate (Scheme 80). This ANRORC mechanism involves the open-chain compound 138 as intermediate (80JHC1733 81JHC953). 

Reaction of nucleophiles with 1,3,5-triazines usually results in ring cleavage. Substitution reactions of the parent system (271) have been limited to the Chichibabin amination, which provides 272, and the preparation of alkyltriazines 273 via an Sn (ANRORC) alkylation (84M16). 

The examples previously presented have featured ANRORC reactions on 6-membered rings. More recently, ANRORC-type rearrangements have been observed in dieir five-membered counterparts, although most examples feature oxadiazoles with bidentate nucleophiles. Spinelli has shown that oxadiazoles with perfluoro-substituents (46) undergo reaction with hydroxylamine to form oxadiazoles (47) with a net reversal in substitution pattern. A perfluoro-group is required at the 5-position for reactivity, as the product 3-perfluoro-oxadiazole (47) is inert to the reaction conditions (preventing reversibility). Hydrazine also efficiently reacts with oxadiazoles to form 1,2,4-triazines. 

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