: Leveraging the unique reactivity profile of donor -acceptor aminocyclopropanes and cyclobutanes allows the preparation of complex nitrogen -substituted molecules. While most reports focus on donor -acceptor strained rings with two geminal carbonyl groups as acceptors, mono carbonyl acceptor systems, despite their synthetic relevance, have been considerably less studied. Herein we describe catalytic annulation reactions of aminocyclopropane and aminocyclobutane monoesters employing silylium catalysis to activate these less reactive donor -acceptor systems.