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 analogue

Abstract

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 [3,3]-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.