Nonheme iron enzymes are versatile catalysts in the biosynthesis of medicinal natural products and have garnered increasing attention as practical catalytic tools in chemical synthesis due to their ability to perform chemically challenging transformations with high stereoselectivity. Recently, several α-ketoglutarate (αKG)-dependent nonheme iron enzymes were found to catalyze the dehydrogenative formation of three-membered cycles in secondary metabolic pathways. For example, BelL catalyzes the cyclopropanation of L-6-nitronorleucine to produce 3-(2-nitrocyclopropyl)alanine during belactosin biosynthesis. TqaL is another fungal enzyme that oxidatively cyclizes L-valine to the aziridine product pleurocybellaziridine. In this study, we analyzed the stereochemical factors influencing the catalytic cyclization reactions catalyzed by these two iron enzymes. It was also demonstrated that the stereoselectivity of the cyclization can be modulated by amino acid substitutions based on the protein structure models. The results suggest that the way in which the radical intermediate interacts with proximal protein residues may also be crucial for achieving a high degree of stereoselectivity in carbon radical-mediated reactions. Therefore, our findings expand our knowledge of stereochemical control by Fe(II)/αKG-dependent oxygenases.​