Preparation of the Chiral Diol (2R,3R)-2-Hydroxymethyl-3-hydroxy-tetrahydropyran from D-Glucose via Reductive Rearrangement of Pseudo-D-glucal Triacetate

Sa？etak Hydrogenation of n-glutal triacetate (1) and pseudo-n-glucal triacetate (2) into (2R,3R)-2-acetoxymethyl-3-acetoxy-tetrahydropyran (4) and the rearrangement of 1 into 2 were investigated. On. hydrogenation, at high catalyst-to-substrate ratio and in the presence of a great excess of diethylamine, compound 1 afforded diacetate 4 in a mixture with triacetate 6, while 2 was quantitatively converted into 4 under standard catalyst-to-substrate (- 1 : 80) ratio. It was established that hydrogenation of both isomers proceeds through the same intermediate 4,6-di-O-acetyl-l,2,3-trideoxy- n-erythro-hex-J-enitol (3) which was fully characterised from its lH_ and 13C-NMRspectra. When hydrogenation of 2 was performed with platinum on carbon in acetonitrile, compound 3 was isolated in 83010yield. The thermal and Lewis acid catalysed rearrangement of 1 into 2 was examined; only zinc(II) chloride in acetic anhydride gave preparatively acceptable yields (60- -70010) of 2. It was demonstrated that with Zn(II) or Mo(VI) ions in AC20 an 1 =:; 2 equilibrium in favour of 2 was attained