Unsymmetrically substituted furoxans. Part 18. Smiles rearrangement in furoxan systems and in related furazans

The preparation and the base-promoted Smiles rearrangement of phenylfurazans (series a), 3-phenylfuroxan (series b) and 4-phenylfuroxan (series c) bearing 2-hydroxyethylthio ( 1), 2-hydroxyethylsulfonyl ( 2), carbamoylmethylthio ( 3) and carbamoylmethylsulfonyl ( 4) functions at the hetero-ring are described. Under similar conditions compounds of the series a and b gave the expected Smiles rearrangment products with the only exception being the amide derivatives 3 which were hydrolysed to their corresponding acid. The behaviour of the 4-phenylfuroxan series to Smiles rearrangment was quite different. Under conditions close to those adopted for the corresponding 3-phenyl isomers, 1c and 2c decomposed into unidentified polar products. 3c afforded as principal product 3-mercapto 4-phenylfurazan while 4c afforded (Z)-2-hydroxyimino-2-phenylacetonitrile. Possible mechanisms of formation of these products are discussed.