Diastereoselective electrochemical carboxylation of chiral alpha-bromocarboxylic acid derivatives: an easy access to unsymmetrical alkylmalonic ester derivatives.
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.
Feroci
Marta
M
Dip. Ingegneria Chimica, Materiali, Materie Prime e Metallurgia, Università La Sapienza, via Castro Laurenziano, 7, I-00161 Roma, Italy. marta.feroci@uniroma1.it
Orsini
Monica
M
Palombi
Laura
L
Sotgiu
Giovanni
G
Colapietro
Marcello
M
Inesi
Achille
A