Synthesis of bi- and tricyclic β-lactam libraries in aqueous medium

Abstract

Water as a solvent is not only inexpensive and environmentally benign, but may allow good reactivity. The present work focuses on the application of a modified Ugi reaction, i.e. the Ugi four-centre three-component reaction (U-4C-3CR), in aqueous medium to construct β-lactam libraries. All the attempted reactions could be successfully performed in water. The reaction conditions under which the precipitation process was effective were investigated; no further work-up or purification was necessary. In several cases when less water-soluble β-amino acids were used, the precipitated products were isolated easily by simple filtration. In other cases, evaporation of the solvent was appropriate for isolation; when the product was crystalline, recrystallization was necessary to obtain the pure final compounds. In water, the yields were higher as compared with the reactions in organic solvents. When bicyclic β-amino acids and the bulky tert-butyl isocyanide were used as starting materials, noteworthy increases in diastereoselectivity were observed.