The N-amino-ribono-1,5-lactam 4 was prepared in two high-yielding steps from the known methanesulfonate 2. Oxidation of 4 with t-BuOCl in the presence of 2,6-lutidine afforded the tetrazene 6 (63%). Oxidation with MnO 2 gave the deaminated lactam 7 (40%), which was also obtained, together with the lactone 8, upon oxidation of 4 with PhSeO 2 H. Oxidation with Mn(OAc) 3 /Cu(OAc) 2 provided the lactam 7 as the major and the dimer 9 as the minor product. Oxidation of 4 with 3 equiv. of Pb(OAc) 4 in toluene at room temperature gave two cyclopentanes, viz. the acetoxy epoxide 10 and the diazo ketone 11 in a combined yield of 78%. Oxidation with Pb(OBz) 4 provided 11 and the crystalline benzoyloxy epoxide 12. The crystal structure of 12 was established by X-ray analysis. The N-amino-glyconolactams 41, 46, and 51 were prepared similarly to 4. Their oxidation with Pb(OAc) 4 provided the diazo ketones 56, 57, and 58 as the only isolable products. Oxidation of the N-aminomannono-1,5-lactam 55 with Pb(OAc) 4 in the presence of DMSO gave the sulfoximine 59. Mannostatin A, a strong a-mannosidase inhibitor, was synthesized from the acetoxy epoxide 10 (obtained in 48% from 4) in seven steps and in an overall yield of 45%. . This synthesis renewed our interest in the transformation of carbohydrates into cyclopentanes. Carbohydrates indeed appear to be ideal starting materials for the synthesis of highly functionalized, enantiomerically pure cyclopentanes. The first general method for the transformation of monosaccharides to cyclopentanes is based on a fragmentation and intramolecular 1,3-dipolar cycloaddition [18]