Isothiourea-Catalyzed Asymmetric Synthesis of β‑Lactams and β‑Amino Esters from Arylacetic Acid Derivatives and <i>N</i>‑Sulfonylaldimines

The isothiourea HBTM-2.1 (5 mol %) catalyzes the asymmetric formal [2 + 2] cycloaddition of both arylacetic acids (following activation with tosyl chloride) and preformed 2-arylacetic anhydrides with <i>N</i>-sulfonylaldimines, generating stereodefined 2,3-diaryl-β-amino esters (after ring-opening) and 3,4-diaryl-<i>anti</i>-β-lactams, respectively, with high diastereocontrol (up to >95:5 dr) and good to excellent enantiocontrol. Deprotection of the <i>N</i>-tosyl substituent within the β-lactam framework was possible without racemization by treatment with SmI<sub>2