GENERATION OF C-1' RADICALS THROUGH A BETA-(ACYLOXY)ALKYL REARRANGEMENT IN MODIFIED PURINE AND PYRIMIDINE NUCLEOSIDES

The synthesis of protected 1',2'-didehydro-2'-deoxyadenosines has been optimized by incorporating a phosphoranylidene protection of the aden ine amino function. These unsaturated adenosines have served as substr ates for the electrophilic iodopivaloyloxylation leading to new nucleo sides modified at the anomeric position. Reaction of halopivaloates 10 , 11 and 12 with tributyltin hydride generates indirectly C-1' radical s through a beta-(acyloxy)alkyl rearrangement. Rate constants for thes e rearrangements have been measured by using free-radical clock method ology and comparison of these data with previous reported results prov ides structural information about the nature of this important class o f radicals. (C) 1997 Elsevier Science Ltd. All rights reserved.