Syntheses and configurations of some heterocyclic amidoximes. X‐Ray crystal structure of 3‐phenyl‐5,6‐dihydro‐2(1 H )‐pyrazinone‐ O ‐methyloxime

O ‐Methyl‐α‐ketophenylacetohydroximoyl chloride ( 1 ) was prepared by the reaction of O ‐methyl‐α‐methoxyphenylacetohydroximoyl chloride ( 5 ) with N ‐bromosuccinimide and concentrated hydrobromic acid. Reaction of 1 with ethylenediamine gave 3‐phenyl‐5,6‐dihydro‐2(1 H )‐pyrazinone‐ O ‐methyloxime ( 6 ). 3‐Phenyl‐5,6‐cyclohexano‐5,6‐dihydro‐2(1 H )‐pyrazininone‐ O ‐methyloxime ( 7 ) was prepared by reaction of 1 with trans ‐1,2‐diaminocyclohexane. The X‐ray structure of 6 has been determined. The crystals are orthorhombic, space group Pbca with a = 10.264(3), b = 18.262(4), c = 23.530(4)Å, V = 4411(2)Å 3 , and Z = 16. The structure, which was refined to R = 0.038 using 1652 observed reflections, shows the amidoxime moiety to be the Z configuration. Reaction of benzohydroximoyl chloride with aziridine gave ( Z )‐aziridinylbenzaldoxime ( 16a ). Ultraviolet irradiation of a benzene solution of 16a gave a mixture of the Z and E isomers 16a and 16b . The E isomer 16b underwent thermal isomerization to 16a at 100°. Reaction of 16a with dimethyl sulfate in sodium hydroxide solution gave ( Z )‐ O ‐methylaziridinylbenzaldoxime ( 17a ). Photoisomerization of a hexane solution of 17a gave a mixture of the Z and E isomers 17a and 17b which were separated by preparative glc. The isomers 17a and 17b are resistant to thermal Z = E isomerization. The mechanisms of thermal isomerization of benzamidoximes are discussed.