After modifications and optimization of the protocol, we returned to test the reaction with the classical ethyl acetoacetate 4a. To understand the process, we monitor the reaction by 1 H NMR. The corresponding spectral data of reaction mixtures before aqueous treatment showed two characteristic peaks around 3.9 and 4.7 ppm, but with simplified multiplicity compared to pure compounds type 5. It could be explained by the silylation of the corresponding N(2)-H. Therefore, we assumed that in this case the reaction also led to cyclic product type 7a. But all our attempts to isolate the product in a pure state failed. One of the possible reasons for such reaction behavior is the high hydrolytic instability of such types of compounds. Such principal difference in stability towards hydrolysis of compound 7a compared with others in the set has no clear explanation. A lot of speculative expectations could be made, but all needed additional experimental investigations, which are out of the scope of the current project.