Intramolecular Direct Aldol Reactions of Sugar Diketones: Syntheses of Valiolamine and Validoxylamine G

A new and stereoselective intramolecular direct aldol reaction of diketones derived from carbohydrates has been developed to construct carbocycles with d-<i>gluco</i>-, d-<i>galacto</i>-, d-<i>manno</i>-, and l-<i>ido</i>-configurations. The stereochemical outcome of the aldol reaction of the diketone is dependent on the base used. Transformation of d-<i>gluco</i>-aldols readily affords valiolamine which also constitutes a formal synthesis of voglibose. Facile conversion of d-<i>gluco</i>-cyclohexanones into validoxylamine G has been achieved in 12 steps with 15.1% overall yield from d-glucose.