Reactions of N-Boc-piperidin-4-one with aromatic aldehydes afforded nitrogen-containing 1,5-diketones in the form of products of intramolecular aldol cyclization, like aza derivatives of tricyclo[7.3.1.02,7]-tridecanone system underlying naturally occurring limonoids. With o-phenylenediamine they enter into a domino-reaction leading to the formation of hydrobenzimidazo[2,1-e]acridine structure. N-Boc-piperidin-4-one in Michael reaction with diarylidenecyclohexanones forms 1,5-diketones undergoing cyclization into hydroxypyran structure.