title: Stereoselective aminoxylation of biradical titanium enolates with TEMPO.
abstract: A highly efficient and straightforward aminoxylation of titanium(IV) enolates from (S)-N-acyl-4-benzyl-5,5-dimethyl-1,3-oxazolidin-2-ones with TEMPO has been developed. A wide array of functional groups on the acyl moiety, including alkyl and aryl substituents, olefins, esters, or α-cyclopropyl, as well as α-trifluoromethyl groups, are well tolerated. This transformation can therefore produce the α-aminoxylated adducts in excellent yields with high diastereomeric ratios (d.r.). In turn, parallel additions to the α,β-unsaturated N-acyl counterparts give the corresponding γ-adducts with complete regioselectivity in moderate to good yields. Removal of the piperidinyl moiety or the chiral auxiliary converts the resultant adducts into enantiomerically pure α-hydroxy carboxyl derivatives, alcohols, or esters in high yields under mild conditions. Finally, a new mechanistic model based on the biradical character of the titanium(IV) enolates has been proposed.
authors.affiliation: Departament de Química Orgànica, Universitat de Barcelona, Carrer Martí i Franqués 1-11, 08028 Barcelona, Catalonia (Spain), Fax: (+34) 93-3397878.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Gómez-Palomino
authors.forename: Miquel
authors.initials: M
authors.lastname: Pellicena
authors.forename: Juan Manuel
authors.initials: JM
authors.lastname: Romo
authors.forename: Ricard
authors.initials: R
authors.lastname: Solà
authors.forename: Pedro
authors.initials: P
authors.lastname: Romea
authors.forename: Fèlix
authors.initials: F
authors.lastname: Urpí
authors.forename: Mercè
authors.initials: M
authors.lastname: Font-Bardia
keywords: TEMPO; aminoxylation; asymmetric synthesis; radical reactions; titanium