An 18O-Labeling Study of the β-(Nitroxy)alkyl and β-(Trifluoroacetoxy)alkyl Radical Migrations: Further Examples of a 1,2-Shift Mechanism

Article abstract of DOI:10.1021/jo00120a028

The results of an 18O labeling study of the β-(nitroxy)alkyl and β-(trifluoroacetoxy)alkyl radical migrations are presented.Phenacyl bromide dimethyl acetal was hydrolyzed with H2(18)O water to give labelled phenacyl bromide and, following borohydride reduction, 18O labeled styrene bromohydrin.Nitration and trifluoroacetylation gave the radical precursors which were allowed to react with tributyltin hydride and AIBN in benzene at reflux.After cleavage to 2-phenylethanol, the rearrangement products were examined by GC-MS.The β-(nitroxy)alkyl migration is found to occur, in benzene to the extent of 64percent through a 1,2-, as opposed to a 2,3-shift, mechanism.The β-(trifluoroacetoxy)alkyl migration occurs 7percent by the 1,2-pathway.It is suggested that, in general, faster ester migrations occur to a greater extent through the 1,2-shift pathway.