Reactivity of the A-CH=N-NR-CX-B system. 4-Methyl-5-hydroxy-5-phenyl-(or thienyl)-2,3,4,5-tetrahydro-1,2,4-triazin-3-ones and their ring contraction products

The behaviour of some monosemicarbazones of phenyl- ( 1a-c ) and thienyl-glyoxal ( 2a-c ) towards cyclizing agents has been investigated. Upon aqueous sodium hydroxide treatment, 4-melhyl-semicarbazones 1a and 2a gave the addition products 3 and 4 , respectively, whereas the 2-methyl- and 2,4-dimethyl derivatives 1b,c and 2b,c gave demolition products only. On the other hand, compounds 1b,c gave the addition product 8 and the triazine 7 , respectively, on treatment with aqueous hydrochloric acid. Bromination of 1a,b gave the bromosemicarbazone 10a and a mixture of 10b and 9 , respectively. Performing the same reaction on 3 and 4 at 115°, the 1,3,4-oxadiazoles 13 and 14 have been obtained. The behaviour of bromosemicarbazones [ 10a,b ] and of the bromo-tetrahydrotriazine 9 towards heating or treatment with base has also been investigated.