Isonitrosoacetophenone hydrazones

The method for the synthesis of 1,2,4-tiiazine 4-oxides 55 involving the condensation of isonitrosoacetophenone hydrazones with aldehydes followed by the oxidation of the intermediates 87 with lead(IV) acetate was reported above (97MC238, 98ZOR423). 

The condensation of amidrazone with isonitrosoacetophenone occurs via formation of the hydrazone 136. The elimination of the ammonia molecule from intermediate 136 yields 3-methyl-6-phenyl-l,2,4-triazine 4-oxide 137 (71LA12). 

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