New Chiral Imidazolidine Ligands for Pd-Catalyzed Asymmetric allylic Alkylation

초록

The development of efficient enantioselective ligands for Palladium-catalyzed allylic substitution reaction is an obvious goal of current research. The phosphinoimidazolidines that have been synthesized from N,N’-dialkylated cyclohexanediamine derivatives showed excellent enantioselectivities in this reaction. Enanthiomerically pure (R,R)-1,2-diaminocyclohexane was converted into its N,N’-dimethyl analogs of type by reaction with ethyl chloroformate in the presence of sodium hydroxide, followed by LAH reduction in THF. The N,N’-diethyl analog was prepared from the corresponding N,N’-diacetyl compound by reduction with LAH in THF so. The N,N’-dibenzyl analog was prepared through reductive amination with benzaldehyde. Chiral phosphinoimidazolidine ligands can be readily synthesized by condensation of N,N’-dialkylated diamine derivatives and 2-(diphenylphosphino) benzaldehyde in the boiling toluene. Pd catalyzed asymmetric allylic substitution of racemic 1,3-diphenyl-2-propenyl acetate with dimethyl malonate was investigated by using new chiral ligands. The excellent levels of enantiomeric excess up to 98% were obtained in high yield