Preparation, Isolation, and Structural Characterization of Lewis Base Iminium Salts of 1,8-Diazabicyclo[5.4.0]undec-7-ene and Their Application as Green Reagents in an Aqueous Medium

We report a state-of-the-art synthesis and isolation procedure for 13 Lewis base iminium salts (LBI) of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), confirming their structures meticulously by different spectral data. The LBIs are distinct from their parent compound (DBU), which provides emphatic support in favor of LBI formation in various DBU-catalyzed reactions. Density functional theory studies of N-sulfonyl LBI of DBU have given new insight into alternate iminium salts, offering a new opportunity for further investigation. We describe the applications of three LBIs as direct reagents for base-free functionalization, broadening their scope as eco-friendly reagents in aquatic media. The Lewis base is recoverable and reusable to prepare the LBI after the reaction. We also document the influence of the N substituent on the chemical shift of these iminium salts.