It was noted that 3a behaves abnormally under Michael reaction conditions. On reaction with piperidine in ethanol in-stead of addition of piperidine to the polarized double bond,: 1 compound with a completely changed carbon skeleton, not containing a piperidine fragment, ie ethyl 2-[N-(diethoxycan bonyl)(ethoxy)-methyl] amino-4-nitrobenzoate (5a) is formed. Use of pyrrolidine, diethylamine, or diisobutylamine also gave rise to 5a.
![diethyl 2-[(2,4-dinitrophenyl)methylidene]propanedioate结构式](https://image.chemsrc.com/caspic/229/87840-68-4.png)
