title: Deeper insight into the mechanism of the reaction of photogenerated metallaketenes and imines.
abstract: The reaction mechanism between Fischer carbene complexes and imines to produce beta-lactams has been studied by a combination of computational (DFT) and experimental methodologies. After the photogeneration of metalla-cyclopropanone species, the reaction initiates by 1,3-migration of the metal fragment from the former carbene carbon atom to the oxygen in the S o hypersurface. In spite of the endothermic nature of this rearrangement, it is biased by the more favorable HOMO(imine)-LUMO+1 interaction in the oxygen-coordinated ketene. This species reacts with the imine to yield metalla-zwitterions, which form the final products through a four electron conrotatory ring closure. The presence of the metal moiety during the whole reaction coordinate is demonstrated by the use of a chiral chromium(0) alkoxycarbene complex, which produces low but significant ee in the reaction with imines. The cis-trans stereoselection derives from the nucleophilic addition of the nitrogen atom of the imine to the oxygen-coordinated ketene, since there are no significant differences between the classical and the metallated processes in the electrocyclation step leading to the final 2-azetidinones.
authors.affiliation: Departamento de Química Orgánica, Facultad de Química, Universidad Complutense, 28040-Madrid, Spain.
authors.forename: Israel
authors.initials: I
authors.lastname: Fernández
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Sierra
authors.forename: María J
authors.initials: MJ
authors.lastname: Mancheño
authors.forename: Mar
authors.initials: M
authors.lastname: Gómez-Gallego
authors.forename: Fernando P
authors.initials: FP
authors.lastname: Cossío
mesh_terms: D000475:Alkenes / Q000737:chemistry* / Q000528:radiation effects*; D001384:Azetidines / Q000138:chemical synthesis* / Q000737:chemistry; D002857:Chromium / Q000737:chemistry / Q000528:radiation effects*; D003198:Computer Simulation; D007097:Imines / Q000737:chemistry / Q000528:radiation effects*; D008956:Models, Chemical; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry / Q000528:radiation effects*; D010777:Photochemistry; D013237:Stereoisomerism; D014466:Ultraviolet Rays
chemical_list: C116379:2-azetidinone; D000475:Alkenes; D001384:Azetidines; D007097:Imines; D009942:Organometallic Compounds; D002857:Chromium