Unveiling the migration reactivity of bicyclic diaziridines: enantioselective synthesis of chiral pyrazolines

Abstract

Ring-opening/cyclization represents a classic reaction of bicyclic diaziridines. In this study, an unprecedented ring-opening/migration cascade process was discovered in the reaction between bicyclic diaziridines and donor–acceptor (D–A) cyclopropanes. By employing a chiral N,N′-dioxide/scandium(III) complex as the catalyst, a diverse array of chiral dihydro-1H-pyrazoles with a stereocenter in the side chain was efficiently synthesized featuring excellent ee values. Control experiments indicated that the substitution on the D–A cyclopropane is of critical importance in determining the cyclization or migration process. When combined with DFT calculations, a plausible reaction mechanism was proposed, which involves a key transition state. This work presents a novel method for accessing pyrazolines and broadens the scope of diaziridine chemistry.