L‐Erythruronic Acid Derivatives as Building Blocks for Nucleoside Analogs. Synthesis of 4′‐ C ‐Aryl‐D‐ribonucleosides

2, 3‐ O ‐Cyclohexylidene‐L‐erythruronic acid (6) available in 83% yield from D‐ribonolactone (7) , was treated with phenvlmagnesium bromide to give the D ‐ribo and L ‐ lyxo derivatives 10 and 11 in high yields ( Scheme 1 and 2 ). The diastereoselectivity depended on the temperature and mode of operation ( Table 1 ). The absolute configuration of 10 and 11 was determined by correlation with ( R )‐ and ( S )phenylethanediol ( 17 and 16 ) respectively, excluding intramolecular hydride shifts during formation of 10 and 11. Reaction of 6 with methcoxymethoxyphenyllithium gave the lactones 18 and 19. The L ‐ lyxo isomer 19 was transformed in high yields into the D ‐ ribo lactone 18 . Compound 10 was transformed into the adenosine analoge 24 by reduction with Diisobutylaluminium hydride, hydrolysis, acetylation and nucleoside synthesis according to Vorbrüggen ( Scheme 3 ). Its structure was deduced from its UV., NMR. and CD. data and from those of the isopropylidene derivative 25 . Similarly, 18 was transformed into the adenosine analog 29 and into the isopropylidene derivative 30 .