Stereocontrolled Syntheses of Deoxyribonucleosides via Photoinduced Electron-Transfer Deoxygenation of Benzoyl-Protected Ribo- and Arabinonucleosides

The stereocontrolled, de novo syntheses of β-2‘-deoxy-, α-2‘-deoxy-, β-3‘-deoxy-, and β-2‘,3‘-dideoxyribonucleosides are described. Strategically protected ribose, arabinose, and xylose glycosylation precursors were synthesized bearing C2-esters capable of directing Vorbrüggen glycosylation. The key step is the regioselective deoxygenation of the desired hydroxyl group as either the benzoyl- or 3-(trifluoromethyl)benzoyl derivative. This deoxygenation is accomplished via a photoinduced electron-transfer (PET) mechanism using carbazole derivatives as the photosensitizer. The syntheses of the desired deoxynucleoside generally proceed in three steps from a common, readily available precursor.