Magtrieve™ (CrO2) and MnO2 mediated oxidation of aldoximes: studying the reaction course
作者:Sandeep Bhosale、Santosh Kurhade、Samir Vyas、Venkata P. Palle、Debnath Bhuniya
DOI:10.1016/j.tet.2010.10.029
日期:2010.12
Magtrieve (TM) (CrO2) and MnO2 mediated oxidation of aldoximes to nitrile oxides were studied in details. In presence of external radical source, TEMPO, these reagents did not furnish nitrile oxides, instead favoured deoximation to aldehydes. A common trend of deoximation was established from electronically tuned aldoximes, which is: aliphatic>aromatic>aldoximes with strong electron-withdrawing group, though the extent of deoximation was less in case of CrO2. Above effects were not observed with chloramine-T and diacetoxyiodobenzene, reagents known to produce nitrile oxides via hydroximoyl halide or equivalent ionic intermediates. A putative reaction mechanism is proposed for MO2 (M=Cr, Mn) mediated oxidation of aldoximes through formation of a nitroso-oxime tautomeric pair. Formation of nitrile oxide is possibly occurred from the oxime tautomer via a sigma-type iminoxy radical intermediate. The deoximation process, dominating in presence of external radical environment, is explained following decomposition of the nitroso tautomer. (C) 2010 Elsevier Ltd. All rights reserved.