Open-Ring Addition to Oxiranes and Aziridines

Along with the development of chiral Lewis acid catalysts, a chiral trialkanolamine (42) has been used to prepare the catalyst (43) (Eq. 19). By use of this zirconium complex as a catalyst, enantioselective addition of the azide to meso epoxides was achieved [20a]. Thus, the oxirane ring was opened by /-PrMe2SiN3 to give the adduct (44) with high enantioselectivity (Eq. 20). In another example, a diamide ligand (45), which behaves as a tetradentate ligand, was used to achieve a similar reaction (Eqs 21 and 22) [20b]. 

Oxophilic early transition metal Lewis acids were shown to react differently from azaphilic Lewis acids when ring-opening of acylaziridines was attempted [21], When A -acyl aziridine 48 was treated with trimethylsilylazide in the presence of a catalytic amount of Cp2Zr(SbF6)2, the product was azide-amide 49, whereas in the presence of Cu(OTf)2 the ring-expansion product, oxazoline 51, was formed (Sch. 1). 

Another example of ring-opening of the oxirane ring is the kinetic resolution of racemic oxiranes by use of chiral Lewis acid catalysts, including Zr(0-t-Bu)4, with (f )-(-F)-binaphthol [22], 

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