Transition-metal-free chiral Brønsted/Lewis acid-catalyzed asymmetric diazo nucleophile-imine reactions

Over the past few decades, transition-metal-free chiral Brønsted acid or Lewis acid-catalyzed asymmetric reactions between diazo nucleophiles and imines have emerged as a pivotal strategy for constructing chiral aziridines or β-amino α-diazo derivatives, achieving remarkable synthetic progress. This review summarizes the research advances in asymmetric aza-Darzens reactions and asymmetric Mannich-type reactions of diazo nucleophiles with imines. It encompasses diverse catalytic systems, including chiral boroxinates, chiral dicarboxylic acids, chiral phosphoric acids, chiral N-triflylphosphoramides, and chiral Lewis acids, with an emphasis on the effects of substrate and catalyst on chemoselectivity. Remaining challenges and future perspectives are presented in this review.