One-pot non-isocyanate urethane synthesis via visible light-activated Curtius rearrangement

Abstract

Curtius rearrangement is a highly versatile and powerful synthetic strategy for converting acyl azides into isocyanates. Herein, we introduce a visible-light-induced non-isocyanate method as an innovative ligation approach for urethane linkage formation, enabling the photochemical in situ generation of isocyanates under mild conditions. We design conjugated acyl azide molecules and successfully integrate these into diverse ligation processes, showcasing their versatility in small molecule synthesis, polymer chain-end functionalization, and surface modification of both inorganic and organic substrates. The resulting small molecules and materials were comprehensively characterized using nuclear magnetic resonance (NMR), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), ultraviolet–visible (UV–Vis) and fluorescence spectroscopy, contact angle (CA) measurements, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Critically, density functional theory (DFT) calculations provided molecular-level insights into the reaction mechanism, revealing how electronic effects influence the initiation efficiency of acyl azides. Our simple yet highly efficient visible-light-driven ligation strategy paves the way for new applications in the fabrication of complex macromolecular architectures, advanced biomaterials, as well as hydrogel networks.