A novel efficient deoxygenation process for N-heteroarene N-oxides.
A novel deoxygenation process for N-heteroarene N-oxides is described. The deoxygenation process has been carried out by utilizing some short C-chain alcohols, benzyl alcohol, or 1-phenylethanol as the solvent in the presence of a base, such as sodium alkoxide or sodium hydroxide. A series of N-heteroarene N-oxides was submitted to the developed conditions to provide the corresponding N-heteroarenes with high yield and excellent selectivity. When the deoxygenation is carried out with benzyl alcohol or 1-phenylethanol as the reaction medium, the process can be performed under very mild conditions, at only 30 degrees C. The deoxygenation process is in contrast to several other methods performed without the presence of any transition metal as a catalyst or stoichiometric reagent. DFT calculations suggest that the alkoxide performs a nucleophilic attack on the N-heteroarene in the ortho or para position. This bond is cleaved homolytically with the overall result being that a single electron-transfer step has occurred. The products of this process are an N-heteroarene N-oxide radical anion and an alkoxyl or benzyloxy radical, depending on the solvent that has been used. Successive steps of the mechanism result in an oxygen transfer from the N-oxide to give the deoxygenated N-heteroarene and 1 equiv of the aldehyde, which is the oxidation product of the solvent alcohol.
Bjørsvik
Hans-René
HR
University of Bergen, Department of Chemistry, Allégaten 41, N-5007 Bergen, Norway. hans.bjorsvik@kj.uib.no
Gambarotti
Cristian
C
Jensen
Vidar R
VR
González
Raquel Rodríguez
RR