Selective Oxidation of Unprotected Carbohydrates to Aldehyde Analogues by Using TEMPO Salts

Abstract

Abstract The primary alcohol function of essentially unprotected carbohydrates (methyl‐α‐ D ‐mannopyranoside, methyl‐α‐ D ‐glucopyranoside and methyl‐α‐ D ‐galactopyranoside) was selectively converted into the corresponding aldehyde in the form of acetals by using TEMPO + BF 4 – (2,2,6,6‐tetramethylpiperidine‐1‐oxoammonium tetrafluoroborate) in organic medium with 2,6‐lutidine as the base. Indeed, organic anhydrous conditions prevent over oxidation of the alcohol group to the carboxylate form. The resulting compounds, methyl‐α‐ D ‐ gluco hexodialdo‐1,5‐pyranoside and methyl‐α‐ D ‐ mano hexodialdo‐1,5‐pyranoside were characterized by NMR and mass spectrometry. Additionally, the results obtained in a TEMPO electrochemically mediated system were compared with those of the pure TEMPO + BF 4 – system, but lower yields were attained under the electrochemical conditions as a result of a very slow reaction rate. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)