Synthesis of methyl 2,3-anhydro-4-deoxy-6-O-methyl-α-DL-lyxo-hexopyranoside

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Abstract
Bromomethoxylation of 2-methoxymethyl-3,4-dihydro-2H-pyran, 1, at −55° gave in 87% yield a 9:1 mixture of 3α-bromo-2β-methoxy-6α-methoxymethyltetrahydropyran (2) and 3β-bromo-2α-methoxy 6α-methoxymethyltetrahydropyran (3) respectively. Of the mixture of 2 and 3, in refluxing methanol containing sodium methoxide, 2 is dehydrohalogenated much more readily than is 3, giving a product that contains at least 95% of the trans-2-methoxy-6-methoxymethyl-5,6-dihydro-2H-pyran, 4. The identity and configuration of 4 was established by its hydrogenation to the known trans-2-methoxy-6-methoxymethyltetrahydropyran, 5. m-Chloroperoxybenzoic acid slowly and selectively converts 4, in 80% yield, to a mixture of methyl 2,3-anhydro-4-deoxy-6-O-methyl-α-DL-lyxo-hexopyranoside (6) (> 95%) and methyl 2,3-anhydro-4-deoxy-6-O-methyl-α-DL-ribo-hexopyranoside, (7) (< 5%).A rationalization is given for the selectivity observed.

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