Aziridination carbenoid-imine transfer

An alternative approach to aziridine synthesis involves transfer of a carbenoid species to imines. Jacobsen achieved the first asymmetric aziridination of imines by transfer of copper carbenoids derived from copper bis-oxazohne catalysts and ethyl diazoacetate onto imines, but this process only proceeds with moderate yield and selectivity. Better results have been achieved by addition of ethyl diazoacetate to imines in the presence of enantiopure Lewis acids such as the boron-based catalysts prepared from vaulted biaryls such as VAPOL (4.154) and B(OPh)3. A range of aryl and alkyl N-benzylaldimines, for example (4.155) and (4.156), undergo aziridination to give ds-aziridines with high ee using this procedure. 

The addition of carbenes and carbenoids to imines and nitriles continues to be a popular approach to aziridines and 2//-azirines. These processes have been well reviewed by Deyrup (B-83MI101-01). Dichlorocarbene and other dihalocarbenes have been added to a wide variety of imines to provide dihaloaziridines. A recent example is shown in Equation (64), illustrating the use of phase-transfer conditions <93H(36)69i). The treatment of azides with excess dichlorocarbene results in the formation of the 2,2,3,3-tetrachloroaziridines (92TL2339). Presumably, the azide is converted by dichlorocarbene to the imidoyl dihalide RN=CC12 which reacts further with dichlorocarbene. Transition metal-promoted reaction of a-diazoesters with imines provides 2-(alkoxycarbonyl)aziridines [Pg.46]

The [2-1-1] cycloaddition reactions allow for the construction of an aziridine skeleton, which are further divided into two types either N1-I-C2 or Ci-l-CiNi modes (Scheme 2.1). The former is achieved by the transfer of nitrenes or nitrenoids (Ni) to alkenes (C2), while the latter by the transfer of carbenes or carbenoids (Ci) to imines (CiNi). Because of limited space, this chapter only covers the... 

---