Tailoring the pore environments of metal-organic frameworks (MOFs) is key to improving their performance and expanding their applicability. Postsynthetic methods, wherein an already synthesized MOF undergoes further chemical reactions, present many advantages for such tailoring and lead to much interesting new chemistry. However, this method has seldom been pushed farther than two reaction steps on the organic component. Here we report a three-step sequence starting from an alkenyl group on the biphenyl backbone of an IRMOF-9 analogue. The alkene is converted to an oxirane group and subsequently to a 1,2-azidoalcohol. The ultimate product is a framework functionalized with an aziridine ring. The reaction efficiency of each step is high, which suppresses the formation of undesired functional groups and the buildup of unintended multivariate frameworks. The synthesis of each framework was attempted via a direct synthetic method employing the appropriately functionalized biphenyldicarboxylate ligand. In general, this met with failure, which demonstrates the power and utility of postsynthetic methods for preparing new materials.