Synthesis of methyl 2,3-dideoxy-DL-alk-2-enopyranosides from furan compounds

A method of converting furan derivatives via 2,3-dideoxy-DL-alk-2-enopyranos-4-uloses, a new class of sugar compounds, into methyl 2,3-dideoxy-DL-alk-2-enopyranosides is described. Furfuryl alcohol, 2(1,2-O-isopropylidene-1,2-dihydroxyethyl)furan, 1(2-furyl)ethanol and 2(2-furyl)glycerol 1,3-diacetate treated with bromine in methanol gave corresponding 2,5-dimethoxy-2,5-dihydrofuran derivatives, which hydrolyzed with diluted sulphuric acid afforded 2,3-dideoxy-DL-pent-2-enopyranos-4-ulose, 2,3-dideoxy-DL-hex-2-enopyranos-4-ulose, 2,3,6-trideoxy-DL-hex-2-enopyranos-4-ulose and 6-O-acetyl-5C-acetoxymethyl-2,3-dideoxy-DL-hex-2-enopyranos-4-ulose, respectively. The latter treated with methyl orthoformate in the presence of Lewis acids yielded corresponding methyl glycosides, which were reduced with sodium borohydride to give appropriate pairs of stereoisomeric methyl 2,3-dideoxy-DL-alk-2-enopyranosides. All stereoisomers were separated and their configuration was established by PMR spectra. 1-O-Acetyl derivatives of 2,3-dideoxy-DL-alk-2-enopyranos-4-uloses were obtained.