engleski

Preparation of the chiral diol (2R, 3R)-2-hydroxymethyl-3-hydroxy-tetrahydropyran from D-glucose via reductive rearrangement of pseudo-D-glucal triacetate

Hydrogenation of D-glutal triacetate (1) and pseudo-D-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-1, 2, 3-trideoxy-D-erythro-hex-1-enitol (3) which was fully characterized from its 1H- and 13C-NMR spectra. When hydrogenation of 2 was performed with platinum on carbon in acetonitrile, compound 3 was isolated in 83% yield. The thermal and Lewis acid catalysed rearrangement of 1 into 2 was examined ; only zinc(II) chloride in acetic anhydride gave preparatively acceptable yields (60-70%) of 2. It was demonstrated that with Zn(II) or Mo(VI) ions in Ac2O an 1-2 equilibrium in favour of 2 was attained.

chiral diol ; (2R, 3R)-2-hydroxymethyl-3-hydroxy-tetrahydropyran

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