[Ring cleavage of N-methoxypyridinium salts by amines]

The 3- and 4-cyano-1-methoxypyridinium salts 1 and 2 reacted with primary and secondary, aliphatic and aromatic amines via ring cleavage to the 5-aminopenta-2,4-dienaloxime ethers 3-10, which were examined concerning their stereochemistry. Contrary to literature no uniform all-trans type products resulted, but the ring opened compounds 3, 4, 7 and 8 contained a cis double bond due to the initial cyclic compound. Partially the corresponding configuration isomers differed only slightly in the energy contents and according to the solvent an equilibrium was observed. Therefore the configuration of the products seems to depend sensitively on the reaction parameters.