title: Self-Sensitized Photooxygenation of 2H-Pyrans: Characterization of Unexpected Products Assisted by Computed Structural Elucidation and Residual Dipolar Couplings.
abstract: The UVA (350 nm) irradiation of an α-pyran in the presence of oxygen led to the unexpected formation of a tetraoxygenated compound whose structure could not be unambiguously determined on the basis of conventional (1)H-(13)C correlated experiments. 1,1-ADEQUATE (adequate double quantum transfer experiment) and 1,n-ADEQUATE combined with computer-assisted structure elucidation software led to two structural possibilities involving the formation of either an epoxide or an oxetane. Residual dipolar couplings allowed not only the identification of the compound as a spiroepoxide but also the determination of its relative configuration. To account for its formation, we propose a bisepoxide intermediate that, as opposed to most α,β-epoxyketones under irradiation, undergoes O-Cβ cleavage probably due to the presence of an extra oxygen substituent in the β position. 1,2-Acyl migration would then proceed stereoselectively to the final product obtained as a single diastereomer.
authors.affiliation: †Instituto de Química Rosario, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario-CONICET, Suipacha 531, S2002LRK Rosario, Argentina.
authors.forename: Martín J
authors.initials: MJ
authors.lastname: Riveira
authors.affiliation: ‡Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Pablo
authors.initials: P
authors.lastname: Trigo-Mouriño
authors.affiliation: ‡Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.|§Departamento de Química Orgánica, Edificio de Ciencias Experimentais, Universidade de Vigo, Campus Universitario, 36310 Vigo, Spain.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Troche-Pesqueira
authors.forename: Gary E
authors.initials: GE
authors.lastname: Martin
authors.affiliation: ⊥Departamento de Química Fundamental, Universidade Federal de Pernambuco, Cidade Universitária, CEP 50.740-540 Recife, Pernambuco, Brazil.
authors.forename: Armando
authors.initials: A
authors.lastname: Navarro-Vázquez
authors.affiliation: †Instituto de Química Rosario, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario-CONICET, Suipacha 531, S2002LRK Rosario, Argentina.
authors.forename: Mirta P
authors.initials: MP
authors.lastname: Mischne
authors.affiliation: ‡Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Roberto R
authors.initials: RR
authors.lastname: Gil