title: Amphiphilic allylation of arylidene-1,3-oxazol-5(4H)-one using bis-π-allylpalladium complexes: an approach to synthesis of cyclohexyl and cyclohexenyl α-amino acids.
abstract: An efficient method for synthesis of cyclohexyl and cyclohexenyl α-amino acids via palladium-catalyzed three-component assemblies followed by ring-closing metathesis (RCM) is described. The present catalytic reaction is successfully extended to substituted benzylidene azlactones 2a-j RCH=(1,3-oxazole): R = alkyl or aryl. The amphiphilic bis-allylation of these substrates has been achieved by replacing toxic allylstannanes with allyltrifluoroborate and the reaction proceeded smoothly to afford the corresponding 1,7-diene derivatives 3a-j in acceptable to good yields. RCM of the resulting octadienes using the first generation Grubbs catalyst gave easy access to stereodefined substituted cyclohexene derivatives 7-11 in high yields. Acid hydrolysis of the oxazolone ring of 7-10 gave protected amino acids 12-16. Debenzoylation of 13 and 15 afforded 1-amino-6-aryl-cyclohex-3-enecarboxylic acids 17 and 18 in excellent yields, respectively. Moreover, catalytic reduction of 13 gave the corresponding cyclohexane derivative 19 which could be debenzoylated to give 1-amino-2-phenylcyclohexene-1-carboxylic acid (20). The structures of compounds 9, 12 and 13 were confirmed by X-ray structural analysis. It is an excellent method for creating a wide range of cyclic α,α-disubstituted α-amino acids.
authors.affiliation: Department of Chemistry, Faculty of Science, University of Tanta, 31527-Tanta, Egypt. genadyafaf@yahoo.com
authors.forename: Afaf R
authors.initials: AR
authors.lastname: Genady
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nakamura
mesh_terms: D000596:Amino Acids / Q000138:chemical synthesis*; D002384:Catalysis; D003510:Cyclohexanes / Q000737:chemistry*; D006868:Hydrolysis; D008958:Models, Molecular; D015394:Molecular Structure; D010080:Oxazoles / Q000737:chemistry*; D010081:Oxazolone / Q000737:chemistry; D010165:Palladium / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D003510:Cyclohexanes; D010080:Oxazoles; D010081:Oxazolone; C506365:Cyclohexane; D010165:Palladium