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

2-Acetamido-2-deoxypentonolactones were synthesized from per-O-acetylated formazans of d-ribose, d- and l-arabinose, respectively. In dimethyl sulfoxide, a novel spontaneous transformation of the per-O-acetyl-pentose formazans into new 3,4,5-tri-O-acetyl-pent-2-enose formazans has been recognized. Additional examples for the occurrence of the isomerism between pseudo-aromatic chelate and open phenylazo-phenylhydrazone system were demonstrated by 1H NMR spectroscopy in both the unprotected pentose formazans and 3,4,5-tri-O-acetyl-pent-2-enose formazans. Computational calculations supported higher stability of the ring form.