Sulfanyl radical promoted C4 '-C5 ' bond scission of 5 '-oxo-3 ',4 '-didehydro-2 ',3 '-dideoxynucleosides

Treatment of C5'-aldehydes 4a, b under mildly basic conditions leads to the formation of 3', 4'-didehydroaldehydes 1a, b and furfural 2. Sulfanyl radical addition to 1a, b eventually gives rise to the lactones 11a, b through C4'-C5' bond scission of the 1,2-dioxetane intermediates 10a, b.