An 18O-Labeling Study of the .beta.-Nitroxyalkyl and .beta.-(Trifluoroacetoxy)alkyl Radical Migrations: Further Examples of a 1,2-Shift Mechanism
作者:David Crich、G. Fredrick Filzen
DOI:10.1021/jo00120a028
日期:1995.7
The results of an O-18 labeling study of the beta-(nitroxy)alkyl and beta-(trifluoroacetoxy)alkyl radical migrations are presented. Phenacyl bromide dimethyl acetal was hydrolyzed with (H2O)-O-18 water to give labeled phenacyl bromide and, following borohydride reduction, O-18 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 beta-(nitroxy)alkyl migration is found to occur, in benzene to the extent of 64% through a 1,2-, as opposed to a 2,3-shift, mechanism. The beta-(trifluoroacetoxy)alkyl migration occurs 7% 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.