For the first time, silver oxide catalyzed SET-oxidative cyclization of an α-amidinoester tethered with an alkene, leading to a novel cyclopropane-fused cyclic amidine, has been developed. This efficient method permits easy access to the pharmaceutically important 3-azabicyclo[n.1.0]alkane framework, having a quaternary centre. The generality of SET oxidative cyclization using persulfate as a co-oxidant has been demonstrated with a wide variety of α-amidinoesters in good yields. Unusual chemoselective dialkylation of amidine with Grignard reagent and regioselective opening of the cyclopropane ring using organocopper reagent have also been developed. © 2019 The Royal Society of Chemistry.