Reaction of N-amino-4,6-dimethylpyrimidinium mesitylene sulfonate with nucleophiles . A 15n-study

Reaction of N-amino-4, 6-dimethylpyrimidinium mesitylene sulfonate with liquid ammonia, with an aqueous solution of sodium hydroxide or with hydrazine leads to 3, 5-dimethylpyrazole. Reaction of this salt with ¹⁵N-labelled hydrazine gave incorporation of nitrogen-15 in 3,5-dimethylpyrazole and in recovered starting material. Evidence has been presented that the initial step in the ring contraction with hydrazine is the addition of the nucleophile to C-2 and C-6. It is suggested that in the presence of a base the reactive species is probably 4,6-dimethylpyrimidinio amide.