Diimine ligands cyclopropanation

Scott et al. [45] prepared diimine derivatives of 2,2 -diamino-6,6 -dimethyl-biphenyl (as structure 37 in Scheme 19) as copper chelates for the catalyzed cyclopropanation reaction. All catalysts were active in this reaction but enan-tioselectivities varied importantly according to the substitution pattern of the imine aryl group only ortho-substituted ligands (by chloride or methyl groups) led to products with measurable enantioselectivity for the model test reaction (up to 57% ee with 37). 

Cai et al. (71) examined the use of dinuclear copper complexes as catalysts in the cyclopropanation reaction. Their ligand design, based on the success exhibited by the Aratani system, incorporates a diimine aryloxide. A comparison of the mononuclear catalyst 99 with the corresponding dinuclear catalyst 100 showed certain modest benefits conferred by the latter, Eq. 52. The authors note that these catalysts are effective at ambient temperature but isolated yields are higher at 50°C with no loss in enantioselectivity. 

The mesityl diimine 88d was as effective a ligand in the aziridination as the 2,6-dichlorophenyl diimine 88a ( 65% ee vs 66% ee) (61). The bound face of the styrene undergoes aziridination (in contrast with Fu s selective crystallization of the wrong face of styrene in his copper-catalyzed cyclopropanation reaction, cf. Section II.A.8). Unfortunately, the potential racemization of 118 (by the mechanism... 

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