NUCLEIC-ACID RELATED-COMPOUNDS .77. 2',3'-DIDEHYDRO-2',3'-DIDEOXY-2'(AND 3')-METHYLNUCLEOSIDES VIA [3,3]-SIGMATROPIC REARRANGEMENTS OF 2'(AND 3')-METHYLENE-3'(AND 2')-O-THIOCARBONYL DERIVATIVES AND RADICAL REDUCTION OF A 2'-CHLORO-3'-METHYLENE ANALOG

Treatment of 5'-O-(tert-butyldiphenylsilyl)-2'(and 3')-deoxy-2'(and 3')-methyleneuridine (and adenosine) derivatives with phenyl chlorothionocarbonate gave the 3'(and 2')-O-phenoxythiocarbonyl intermediates, which underwent spontaneous [3,31-sigmatropic rearrangement to give the 2',3'-didehydro-2',3'-dideoxy-2'(and 3')-(phenoxycarbonylthio)methyl analogues. These allylic thioesters were subjected to tributylstannane-mediated hydrodesulfurization and deprotection to give 2',3'-didehydro-2',3'-dideoxy-2'(and 3')-methyluridine (and adenosine). Tributylstannane-mediated hydrodehalogenation of a 2'-chloro-2',3'-dideoxy-3'-methyleneuridine derivative afforded the 2',3'-didehydro-2',3'-dideoxy-3'-methyl product of allylic transposition exclusively.