title: Mechanistic studies of highly enantio- and diastereoselective aza-Petasis-Ferrier rearrangement catalyzed by chiral phosphoric acid.
abstract: The precise mechanism of the highly anti- and enantioselective aza-Petasis-Ferrier (APF) rearrangement of hemiaminal vinyl ethers catalyzed by a chiral phosphoric acid was investigated by undertaking experimental and theoretical studies. The APF rearrangement is characterized by the following unique mechanistic features: (i) efficient optical kinetic resolution of the starting racemic hemiaminal vinyl ether, (ii) enantioconvergent process from racemic hemiaminal vinyl ethers to optically active β-amino aldehyde products, and (iii) anomalous temperature effects on the enantioselectivity (enantioselectivity increases as reaction temperature increases). The following experiments were conducted to elucidate the unique mechanistic features as well as to uncover the overall scheme of the present rearrangement: (A) X-ray crystallographic analysis of the recovered hemiaminal vinyl ether to determine its absolute configuration, (B) rearrangements of enantiomerically pure hemiaminal vinyl ethers to validate the stereochemical relationship between the hemiaminal vinyl ethers and β-amino aldehydes, (C) theoretical studies on the transition states of the C-O bond cleavage and C-C bond formation steps to gain an insight into the optical kinetic resolution of the hemiaminal vinyl ether and the origin of the stereoselectivity, as well as to elucidate the overall scheme of the present rearrangement, and (D) crossover experiments of two hemiaminal vinyl ethers having different vinyl ether and aliphatic substituents to comprehend the mechanism of the anomalous temperature effect and the enantioconvergent process. The results of experiments and theoretical studies fully support the proposed mechanism of the present anti- and enantioselective APF rearrangement.
authors.affiliation: Department of Chemistry, Graduate School of Science, Tohoku University , Aoba-ku, Sendai 980-8578, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Terada
authors.forename: Takazumi
authors.initials: T
authors.lastname: Komuro
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Toda
authors.forename: Toshinobu
authors.initials: T
authors.lastname: Korenaga
mesh_terms: D000447:Aldehydes / Q000737:chemistry; D002384:Catalysis; D007700:Kinetics; D008958:Models, Molecular; D010756:Phosphoric Acids / Q000737:chemistry*; D013237:Stereoisomerism; D014753:Vinyl Compounds / Q000737:chemistry*
chemical_list: D000447:Aldehydes; D010756:Phosphoric Acids; D014753:Vinyl Compounds; C100195:vinyl ether; C030242:phosphoric acid