Catalytic asymmetric cycloadditions of reactive ketene intermediates provide new opportunities for the production of chiral heterocyclic molecules.Though known for over 100 years,ketenes still remain underexplored in the field of transition-metal(TM)-catalyzed asymmetric cycloadditions because(1) ketenes,as highly electron-deficient species,are possibly unstable to low-valance TMs(i.e.,decarbonylation or aggregation) and(2) the conventional thermal synthesis of ketenes from acyl chlorides and amines may be incompatible with TM catalysis(i.e.,reactive acyl chloride and amine-hydrochloride by-products).