HYDROGENOLYSIS OF CARBOHYDRATES: VII. METHYL β-L-ARABOPYRANOSIDE-1-C14

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Abstract
Methyl β-L-arabopyranoside-1-C14 was hydrogenolyzed in the presence of copper chrome oxide catalyst at 250 °C, yielding an approximately equimolar mixture of optically inactive cis- and trans-3,4-dihydroxytetrahydropyran-C14, together with 2,3-dihydroxypentane-C14. The latter was formed by reductive ring-opening of the tetrahydropyrandiols. Ether cleavage of each of the cyclic diols afforded 1,2,3,5-tetrahydroxypentane-C14 in which the tracer was distributed about equally between carbons 1 and 5. Carbon-14 in the pentanediol was distributed in a similar manner. The results show that both the 2- and 4-hydroxyl groups of the original pentoside are prone to reductive cleavage, and that cis- and trans-glycol groups in the cyclic diols are formed by isomerization. They suggest that hydrogenolysis of the methoxyl group takes place initially, accompanied by isomerization, to give a mixture of tetrahydropyrantriols in which the 2- and 4-hydroxyl groups have equivalent reactivity.