title: Catalytic Approach for the Formation of Optically Active Allyl alpha-Amino Acids by Addition of Allylic Metal Compounds to alpha-Imino Esters.
abstract: A new catalytic enantioselective approach for the formation of allyl alpha-amino acid derivatives by reaction of N-tosyl alpha-imino esters with allyl stannanes and silanes catalyzed by chiral copper(I) complexes has been developed. A series of different BINAP and phosphine-oxazoline (P,N) ligands have, in combination with various Lewis acids, been tested as chiral catalysts for allylation of N-tosyl alpha-imino esters. It has been found that both type of ligands, in combination with copper(I) salts, give highly valuable unsaturated alpha-amino acid derivatives. The reaction has been investigated for different allyl stannanes and silanes, and it has been found that tri-n-butyl allyl stannane gives the best results of the simple allyl compounds tested, leading to gamma,delta-unsaturated alpha-amino acid derivatives in up to 94% yield and with up to 83% ee, which can be improved to be >95% ee by recrystallization. The reaction has also been investigated using different acyclic and cyclic allyl stannanes leading to various types of unsaturated alpha-amino acid derivatives in very high yield (up to 95%) and with up to 98% ee. The stereochemistry and absolute configurations of the allyl alpha-amino acid derivatives have been determined by X-ray analysis, and it is suggested that the reaction takes place as an ene-like reaction.
authors.affiliation: Center for Metal Catalyzed Reactions, Department of Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark, and Department of Organic Chemistry, Building 201, Technical University of Denmark, DK-2800 Lyngby, Denmark.
authors.forename: Xiangming
authors.initials: X
authors.lastname: Fang
authors.forename: Mogens
authors.initials: M
authors.lastname: Johannsen
authors.forename: Sulan
authors.initials: S
authors.lastname: Yao
authors.forename: Nicholas
authors.initials: N
authors.lastname: Gathergood
authors.forename: Rita G.
authors.initials: RG
authors.lastname: Hazell
authors.forename: Karl Anker
authors.initials: KA
authors.lastname: Jørgensen