“…Nitrogen-containing aldehydes and acetals are widely used in the heterocycles synthesis [ 14 , 15 ]. Earlier, we have described the approach to 2-substituted pyrrolidine derivatives based on the in situ generation of a cyclic iminium ion from 4-aminobutanal acetals (4,4-diethoxybutan-1-amines) and its trapping by various nucleophiles [ 16 , 17 , 18 ]. Our preliminary studies indicate that N -(2,2-dialkoxyethyl) ureas are also capable of the formation of cyclic imidazolinium cations and the reaction results in cyclic urea derivatives—imidazolidinones or benzo [ d ] [1,3] diazepinones [ 19 ].…”