AbstractAn efficient method has been developed for the synthesis of N‐aryl‐1,2,4‐dioxazolidines, N‐aryl‐tetraoxaspiroalkanes, and N‐aryl‐hexaoxadispiroalkanes by cycloaminomethylation of OH acids (hydrogen peroxide, gem‐bis‐hydroperoxides, and 1,1′‐peroxybis(1‐hydroperoxycycloalkanes)) with 1,3,5‐triaryl‐1,3,5‐triazinanes in the presence of lanthanide catalysts. The eight‐membered azadiperoxides were shown to exhibit a high cytotoxic activity against Jurkat, K562, and U937 tumor cells and Hek296 immortalized normal cells. The cytotoxic activity of Fe(II)‐treated azadiperoxides against Jurkat tumor cells was studied; these compounds were shown to in Keywords: Catalysis; Cycloaminomethylation; Hydrogen peroxide; Gem‐bis‐hydroperoxides; 1,1′‐Peroxy‐bis(1‐hydroperoxycycloalkanes); Azaperoxides; Cytotoxic activity initiate cell autophagy.