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A new ring transformation reaction has been studied by treating 6-or 5,6-disubstituted 4-(methylthio)-2-0~0-2H-pyran-3-carbonitriles 2 with hydrazine and methylhydrazine leading to polysubstituted pyrazoles 4, 5, 6.In view of a subsequent synthesis, we intended to develop a simple procedure for the preparation of 5(3)-aryl-3(5)-(cyanomethyl)-Imethyl-1 H-pyrazoles. Procedures in vogue for the synthesis of pyrazoles involve, in general, cyclocondensation between a hydrazine system and a three-carbon component with electrophilicity at terminal carbon atoms. A substrate fulfilling the above conditions and bearing a built-in potentiality for eventual elaboration of a CH,CN side chain was sought for. The 6-aryl-4-(methylthio)-2-0~0-2H-pyran-3-carbonitriles 2, endowed with two sets of such functionalities, (2-4-C-3 -CN and C-4-C-5 -(2-6, in the molecule, was recognized attractive. 2 has earlier been reported to react with hydrazine to afford 1 and 3'), a claim which could not be substantiated in our hands. On the contrary, a reexamination of the procedure under strictly reported conditions') gave invariably pyrazoles 4. The authenticity of this reaction was further checked by replacing hydrazine with methylhydrazine which afforded 5 and 6. These observations suggest the involvement of C-4 and C-6 in pyrazole formation instead of C-4 and CN as claimed earlier. The reaction seems to be initiated by a Michael addition of hydrazines at C-4 in 2 with expulsion of methanethiol and simultaneous ring opening followed by recyclisation and decarboxylation to yield the (cyanomethy1)pyrazoles (Scheme 1). Nevertheless, the initial attack at C-6 by hydrazines cannot be excluded as well.Both the positional isomers 5 and 6 were separated from the reaction mixture by column chromatography. Their structures were established by 'H-and 13C-NMR analyses. The downfield resonances for aryl and heteroaryl protons of demethylpyrazoles resembled in pattern and position to those of 6 whereas, in cases of isomers 5, the NCH3 invariably exerted a shielding effect on protons of aryl and heteroaryl substituents at C-5. This diagnostic feature, bearing a testimony to an earlier observation in case of n i~o t i n e~,~) , may be utilized for distinguishing the isomers 5 and 6.The reaction between 5-(3,4-dimethoxyphenyl)-6-methyl-4-(methylthio)-2-oxo-2H-pyran-3-carbonitrile (2c) and methylhydrazine gave a single product whose structure as 5 e was established by observing a strong NOE between 5-CH3 and NCH3 groups.This observation constitutes the first example of such a ring transformation reaction.

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