title: Diastereoselective electrochemical carboxylation of chiral alpha-bromocarboxylic acid derivatives: an easy access to unsymmetrical alkylmalonic ester derivatives.
abstract: The diastereoselective electrochemical carboxylation of chiral N-(2-bromoacyl)oxazolidin-2-ones has been studied. This reaction was carried out by cathodic reduction of the C-Br bond, in the presence of carbon dioxide, followed by treatment with diazomethane. The yields and the diastereomeric ratio of the two epimeric alkylmalonic acid derivatives are strongly affected by various factors: solvent-supporting electrolyte system, temperature, electrode material, electrolysis conditions, oxazolidinone moiety. The higher yields (88%) were obtained starting from N-(2-bromopropionyl)-4R-phenyloxazolidin-2-one 1a, but with poor diastereoselectivity (61:39). The two epimers were easily separated by flash chromatography. The best results were achieved using a different chiral auxiliary: Oppolzer's camphor sultam. Starting from 1j a good yield in carboxylated product was obtained (80%) with excellent diastereoselectivity (98:2). These chiral alkylmalonic acid derivatives are valuable building blocks in the synthesis of molecules with biological activity and of chiral propane-1,3-diols derivatives.
authors.affiliation: Dip. Ingegneria Chimica, Materiali, Materie Prime e Metallurgia, Università La Sapienza, via Castro Laurenziano, 7, I-00161 Roma, Italy. marta.feroci@uniroma1.it
authors.forename: Marta
authors.initials: M
authors.lastname: Feroci
authors.forename: Monica
authors.initials: M
authors.lastname: Orsini
authors.forename: Laura
authors.initials: L
authors.lastname: Palombi
authors.forename: Giovanni
authors.initials: G
authors.lastname: Sotgiu
authors.forename: Marcello
authors.initials: M
authors.lastname: Colapietro
authors.forename: Achille
authors.initials: A
authors.lastname: Inesi