Chiral Aldehydes by Ring Contraction of Pento- and Hexopyranoside Epoxides
The chiral aldehydes (-)-(2S,5S)- and (-)-(2S,5R)-2-[[[dimethyl( 1,1,2-trimethylpropyl)silyl]oxy]methyl]-5-methoxy-2,5-dihydrofuran-3-carbaldehyde (2 and 4) were synthesized in 60 and 15% yield, respectively, by lithium bromide induced rearrangement of 6-O-silylated methyl 2,3- and 3,4-anhydro-a- and -d-D-hexopyranosides, obtained in two steps from methyl α- and β-D-glucopyranoside. Rearrangement