Kinetic Resolution of 2H-Azirines by Asymmetric Imine Amidation

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.

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

The unprecedented enantioselective aza-benzoin reaction of aldehydes with 2H-azirines was developed by utilizing a chiral N-heterocyclic carbene as the catalyst. A wide range of corresponding aziridines can be obtained in good yields with high enantioselectivities. The obtained optically active aziridines should be useful in the synthesis of other valuable molecules.

Enantioselective Reaction of 2H-Azirines with Phosphite Using Chiral Bis(imidazoline)/Zinc(II) Catalysts

The first highly enantioselective nucleophilic addition reaction of phosphites with 2H-azirines has been developed. The reaction was applied to various 3-substituted 2H-azirines using novel chiral bis(imidazoline)/Zn^II catalysts to afford products in good yield with high enantioselectivity. The transformation of the obtained optically active aziridines showed that 2H-azirines act as either α,β- or β,β-dicarbocationic amine synthons.

Highly Enantioselective Synthesis of Indolines: Asymmetric Hydrogenation at Ambient Temperature and Pressure with Cationic Ruthenium Diamine Catalysts

A highly enantioselective synthesis of indolines by asymmetric hydrogenation of 1H-indoles and 3H-indoles at ambient temperature and pressure, catalyzed by chiral phosphine-free cationic ruthenium complexes, has been developed. Excellent enantio- and diastereoselectivities (up to >99 % ee, >20:1 d.r.) were obtained for a wide range of indole derivatives, including unprotected 2-substituted and 2,3-disubstituted 1H-indoles, as well as 2-alkyl- and 2-aryl-substituted 3H-indoles.