Enantioselective carbonyl-ene reactions of arylglyoxals with a chiral palladium(II)-BINAP catalyst

The palladium(II)-BINAP-catalyzed enantioselective carbonyl-ene reactions between ten arylglyoxals and five alkenes were systematically investigated and demonstrated good to excellent enantioselectivities with high ee values of up to 93.8 %. The results showed that both arylglyoxals and alkenes exert evident effects on the enantioselectivity. Particularly, the ortho-methyl substituents of the substrates could increase the enantioselectivity. The achieved excellent enantioselectivities may be due to the corresponding substrate matches well fitting the chiral space created by the chiral palladium (II)-BINAP catalyst. The ortho-methyl substituents may improve the fitting of the substrate match to the chiral space created by the chiral catalyst, hence the enantioselectivity is improved. When using dienes (1,4-diisopropenylbenzene and 1,3-diisopropenylbenzene) as substrates in this reaction, only one of the two carbon-carbon double bonds participated into the reaction affording tetrafunctional organic compounds with moderate enantioselectivities of up to 83.8 % ee. The chiral Lewis acid palladium(II) catalyst incorporating (R)-BINAP, which is a conformationally restricted chiral ligand, is very stable in ionic liquids and could be recycled 21. times with retention of the high enantioselectivity.