Azides by Ring Opening of Epoxides and Aziridines

Kinetic studies on the mechanism of asymmetric (salen)Cr(ni) catalysed ring opening of epoxides by TMSN3 provide strong support for a mechanism involving catalyst activation of both nucleophile and electrophile by two different catalyst molecules. This observation led Jacobsen et al. to construct covalently linked dimeric salen complexes 

The use of immobilized (salenX2r(lll) complexes has been reported. The impregnation of the complex on silica resulted in a heterogeneous catalyst for the asymmetric ring opening of epoxides with TMSNs.  

The reaction of the mixture 112 and 113 leads to the corresponding azido-product 115 together with 1,2-epoxy-terpene 113. Therefore, 112 was selectively transformed and epoxide 113 was recovered. On the other hand, the authors could conclude that the dia-stereoselectivity observed was due to the presence of the C4-substitnent at the starting epoxides, which forces the substrate into the more stable conformation and consequently blocks the approach of the Cr-Ns species from one side. 

123a 54% (isomer ratio 3-N3/2-N3 = 40 1) 123b 63% (isomer ratio 3-N3/2-N3 = 35 1) 

Jacobsen et al. described the enantioselective ring opening of meso aziridines by TMSN3 catalysed by tridentate Schiff base chromium complexes. Using 133 as the catalyst, high yields of conversion to azidoamines and high levels of enantioselectivity are 

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