title: Conformational preferences of methacrolein in Diels-Alder and 1,3-dipolar cycloaddition reactions.
abstract: A B3LYP/6-31G* study has been carried out for the reactions of methacrolein with cyclopentadiene, parent nitrone, 1-pyrroline-1-oxide, and (Z)-C,N-diphenylnitrone, in which the coordination of a Lewis acid (borane) and the solvent polarity (dichloromethane) have been taken into account. Calculated activation parameters, regioselectivities (for 1,3-dipolar cycloaddition reactions), and endo/exo stereoselectivities show good agreement with available experimental data. Gas-phase calculations show a varied behavior of the s-cis/s-trans TS stability for noncatalyzed reactions (from the systematic s-cis preference for the cyclopentadiene reaction to the systematic s-trans predilection encountered in the diphenylnitrone cycloaddition). BH3 coordination leads to a preferential stabilization of s-trans TSs in the reactions of cyclopentadiene (exo approach) and diphenylnitrone but a larger stabilization of s-cis structures in the processes involving the parent nitrone or 1-pyrroline-1-oxide. Additionally, a rather systematic preferential stabilization of s-trans structures is induced by solvent polarity in most reactions. As a consequence, an s-trans preference is predicted in solution for both thermal and catalyzed types of reactions in most approaches. Such a conclusion is consistent with some experimental results suggesting a preference for a particular conformation of the methacrolein-Lewis acid complexes.
authors.affiliation: Departamento de Química InorgAnica, Instituto de Ciencia de Materiales de Aragón, Instituto Universitario de CatAlisis Homogénea, Facultad de Ciencias, Universidad de Zaragoza-CSIC, Pedro Cerbuna 12, E-50009 Zaragoza, Spain.
authors.forename: Carmen
authors.initials: C
authors.lastname: Barba
authors.forename: Daniel
authors.initials: D
authors.lastname: Carmona
authors.forename: José Ignacio
authors.initials: JI
authors.lastname: García
authors.forename: María Pilar
authors.initials: MP
authors.lastname: Lamata
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Mayoral
authors.forename: Luis
authors.initials: L
authors.lastname: Salvatella
authors.forename: Fernando
authors.initials: F
authors.lastname: Viguri
mesh_terms: D000171:Acrolein / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D000814:Aniline Compounds / Q000737:chemistry; D001596:Benzylamines / Q000737:chemistry; D001880:Boranes / Q000737:chemistry; D003198:Computer Simulation; D003497:Cyclic N-Oxides / Q000737:chemistry; D003500:Cyclization; D003517:Cyclopentanes / Q000737:chemistry; D008752:Methylene Chloride / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D009589:Nitrogen Oxides / Q000737:chemistry; D011759:Pyrrolidines / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: C517334:1-pyrrolidine-1-oxide; D000814:Aniline Compounds; D001596:Benzylamines; D001880:Boranes; C517335:C,N-diphenylnitrone; D003497:Cyclic N-Oxides; D003517:Cyclopentanes; D009589:Nitrogen Oxides; D011759:Pyrrolidines; C015388:nitrones; D008752:Methylene Chloride; D000171:Acrolein; C039175:methacrylaldehyde