Steric structure of 1-hydroxy-2,3-dimethyl-1,4,5-triaza-1,3,5-hexatrienes

Condensation of 3-hydroxyimino-2-butanone hydrazone with aromatic and unsat urated aldehydes and methyl ketones leads to formation of 1-hydroxy-2,3-dim ethyl-1,4,5-triaza-1,3,5-hexatrienes which exist as a single open-chain con former. An exception is 6-(2-furyl)-1-hydroxy-2,3-dimethy1-1,4,5-triaza-1,3 ,5-hexatriene which exists in solution as a 4:1 mixture of E and Z isomers with respect to the C=N bond. The reaction of 3-hydroxyimino-2-butanone hyd razone with glyoxal involves both carbonyl groups of the latter to give the corresponding osazone.