title: 1,3-dipolar cycloadditions of diazoalkanes to activated sulfoxides: influence of Lewis acids.
abstract: [reaction: see text] The reactions of diazomethane and diazoethane with (S)-3-p-tolylsulfinylfuran-2(5H)-one (3) and its 4-methyl derivative (4) have been studied. The sulfinyl group was able to completely control the pi-facial selectivity of all these reactions, which decreased when the polarity of the solvent increased and could be inverted in the presence of Lewis acids, Yb(OTf)(3) being the most efficient catalyst. This behavior made possible the stereodivergent synthesis of diastereoisomeric pyrazolines in almost quantitative yields and de's higher than 98%. The endo/exo selectivity was also complete in reactions of 3 with diazoethane, whereas 4 afforded an easily separable 1:1 mixture of diastereoisomers. Steric factors accounts for the endo/exo selectivity, whereas electrostatic interactions must also be considered to explain the facial selectivity.
authors.affiliation: Departamento de Química Orgánica, Universidad Autónoma de Madrid, Cantoblanco, Spain. joseluis.garcia.ruano@uam.es
authors.forename: José L García
authors.initials: JL
authors.lastname: Ruano
authors.forename: M Teresa
authors.initials: MT
authors.lastname: Peromingo
authors.forename: Marina
authors.initials: M
authors.lastname: Alonso
authors.forename: Alberto
authors.initials: A
authors.lastname: Fraile
authors.forename: M Rosario
authors.initials: MR
authors.lastname: Martín
authors.forename: Amelia
authors.initials: A
authors.lastname: Tito