ketose derivatives, having substituents at C-1, were synthesised from the acetylated aldehydo forms of D -galactose, D -glucose, and D -mannose, using (acetyl- and aroyl-methylene) triphenylphosphoranes. The structures of the ketose derivatives were examined by i.r. and u.v. spectroscopy. In the deacetylated products, the presence of acyclic ketose structures was indicated by periodateoxidation studies