An unprecedented version of the Ugi three-component coupling
reaction is reported in which isocyanides react with unprotected
aldoses as biorenewable aldehyde components and acyclic amidines
as amine components. The reaction proceeds through [4 + 1] cycloaddition
of a conjugated imine intermediate with the isocyanide followed
by dehydrative ring transformation of the resulting 4-amino-5-(polyhydroxyalkyl)imidazole
to afford imino sugar-annulated imidazoles in excellent
yields (86-95%). The procedure is performed in
one pot in the presence of a nanoclay (K-10) catalyst, and can be
expeditiously effected under solvent-free microwave-irradiation
conditions.
heterocycles - carbohydrates - cyclizations - multicomponent reactions - catalysis - Ugi
reaction
