Synthesis and hydrogenolysis of the methylene, ethylidene, isopropylidene, and diastereoisomeric 1-phenylethylidene acetals of β-l-arabino- and α-l-rhamnopyranoside derivatives
diastereoisomers of 1-phenylethylidene acetals (acetophenone acetals) of methyl and benzyl β- l -arabinopyranoside and α- l -rhamnopyranoside were prepared. Acetal-exchange reactions gave only the endo -phenyl isomers; their 2- O - and 4- O -acetyl derivatives were isomerised into the exo -phenyl compounds. 1 H-N.m.r. data were used to determine the absolute configuration at the acetal carbon atom in these compounds