title: Diastereoselective Michael additions of N-Boc-2-(tert-butyldimethylsiloxy)pyrrole to 2-(Arylsulfinyl)-1,4-benzoquinones.
abstract: Reactions of 2-(arylsulfinyl)-1,4-benzoquinones 1a-c with N-(tert-butoxycarbonyl)-2-(tert-butyldimethylsiloxy)pyrrole 2 have been studied under different catalytic conditions. Under BF(3).OEt(2) catalysis, reactions were completely stereoselective leading to the Michael-type adducts 3, whereas in the presence of SnCl(4) diastereomeric mixtures of the pyrrolo[3,2-b]benzofuranes 5 and 6 were obtained. The latter products result from a tandem process involving the Michael reaction followed by an intramolecular cyclization of the intermediates 3 and 4, the first step being hardly stereoselective. Reactions catalyzed by Eu(fod)(3) evolved in a highly stereoselective manner yielding the products 3 or 5 depending on the electronic density of the arylsulfinyl group.
authors.affiliation: Departamento de Química Orgánica (E.T.S.I.I.), Universidad de Valladolid, Paseo del Cauce s/n, 47011-Valladolid, Spain.
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Arroyo
authors.forename: Mónica
authors.initials: M
authors.lastname: de Paz
authors.forename: Justo F
authors.initials: JF
authors.lastname: Rodríguez
authors.forename: M Ascensión
authors.initials: MA
authors.lastname: Sanz-Tejedor
authors.forename: José L
authors.initials: JL
authors.lastname: García Ruano