Catalytic Enantioselective Aza-Benzoin Reactions of Aldehydes with 2H -Azirines

Copper-Catalyzed Highly Enantioselective Addition of a Silicon Nucleophile to 3-Substituted 2H-Azirines Using an Si-B Reagent

3-Substituted 2H-azirines can be considered strained cyclic ketimines, and highly enantioselective addition reactions of silicon nucleophiles to either acyclic or cyclic ketimines have been elusive so far. The present work closes this gap for those azirines by means of a copper-catalyzed silylation using a silyl boronic ester as a latent silicon nucleophile. The resulting C-silylated, unprotected (N-H) aziridines are obtained in high yields and with excellent enantioselectivities and can be further converted into valuable compounds with hardly any erosion of the enantiomeric excess.

Synthesis of Quaternary Spirooxindole 2H-Azirines under Batch and Continuous Flow Condition and Metal Assisted Umpolung Reactivity for the Ring-Opening Reaction

An efficient and new approach for the synthesis of spirooxindole 2H-azirines via intramolecular oxidative cyclization of 3-(amino(phenyl)methylene)-indolin-2-one derivatives in the presence of I₂ and Cs₂ CO₃ under batch/continuous flow is described. This method is mild and facile to synthesize a variety of spirooxindole 2H-azirines derivatives in gram-scale. Furthermore, we have synthesized spiroaziridine derivatives from spirooxindole 2H-azirines derivatives via addition of Grignard reagent. In addition, we discloses an metal assisted attack of Grignard nucleophile at N-centre rather than C- of the spirooxindole 2H-azirines, which concurrently underwent ring opening of transient aziridines to afford N-substituted Z-3-(aminophenyl)indolin-2-one. A plausible mechanism for azirination and ring-opening reaction is also presented.

Enantioselective Reaction of 2H-Azirines

2H-Azirines are useful precursors for the synthesis of a variety of chiral aziridine and amine derivatives with a range of biological activities. Owing to the ring strain and the presence of a C=N double bond, 2H-azirines are more reactive than other types of ketimine, and undergo a range of enantioselective reactions, including reduction and Diels-Alder reactions, as well as nucleophilic addition to the C=N double bond. Therefore, the enantioselective reactions of 2H-azirines has become a hot topic, in particular within the last few years. In this Minireview, we focus on the enantioselective reactions of 2H-azirines by using catalytic or stoichiometric amounts of chiral additives, the reaction mechanisms, and the applications of these reactions of 2H-azirines and related compounds in organic synthesis.