Transformation of aldose formazans. Novel synthesis of 2-acetamido-2-deoxypentonolactones and a new pent-2-enose formazan

► Nucleophilic replacement of the AcO-2 group of per-O-acetyl pentose formazans. ► Regiospecific and stereoselective introduction of NH2-function into the sugar chain. ► Novel synthesis of 2-acetamido-2-deoxy-pentonolactones. ► New formation of acetylated pent-2-enose formazans. ► Isomerism of the formazyl moiety between the chelate and the open forms.