Synthesis of methyl 2,3,6-trideoxy-4-C-(2,5-dimethoxybenzyl)-α-L-threo-HEX-2-enopyranoside

Methyl 2,3-O-protected alpha-L-lyxopyranosid-4-uloses (9 and 19), obtained from L-rhamnose (8), react with 2,5-dimethoxybenzyllithium to afford, with high stereoselectivity, compounds 10a and 20a, respectively. After protection of the 4-OH group, ethers 10b and 20b were transformed via vic-diol deoxygenation reactions into the title compound 3 and its 4-O-benzyl derivative 17. The configuration at C-4 in the alcohol 10a and the acetate of its regioisomer 12b has been established by single crystal X-ray analysis.