| Asymmetric allylic oxidation of cyclic olefins using catalytic copper(I) malonyl-derived bisoxazoline (Box), naphthylisoquinoline oxzaoline, 2,6-pyridyl-bisoxazoline (PyBox) and 2,2′-camphor-derived bipyridyl complexes and perbenzoate peresters was investigated to give allyl ester products with high selectivities (up to 99% ee) and moderate to good yields (40–80%) under varied reaction conditions. Unique ligand substrate combinations have been identified for high enantioselectivity with reasonable reactivity using eight prepared malonyl-derived bisoxazoline copper (I) tetrkisacetonitrile hexafluorophosphate complexes at −20°C in acetonitrile. An opposite effect of the oxzaoline ring substituent on both reactivity and selectivity has been recognized between tert-butyl and phenyl groups. A 13C NMR study on a Cu(I)/Box complex in deuterated acetonitrile at −35°C ruled out formation of a η2 copper/alkene complex in the reaction pathway. Novel chiral ligands including dinaphthyl-Box, naphthylisoquinoline oxazoline, Pybox and 2,2′-camphor-derived bipyridyl ligand were also explored. |
