Action of Molybdate Anion on d-Glucosone: Catalytic Conversion to Aldonates Involving C1-C2 Transposition

Treatment of the osone (aldos-2-ulose), d-[1-¹³C]glucosone (1 ¹), with sodium molybdate at 90° for 30 h gave a mixture of d-[2-¹³C]gluconate (2 ²) and d-[2-¹³C]mannonate (3 ²) in an 85:15 ratio, indicating that the reaction proceeds with C1-C2 transposition similar to that observed previously with aldoses. Reactions with several singly and doubly ¹³C-labeled isotopomers of 1 confirmed this transposition. In contrast to the aldose reaction, the reaction with 1 is irreversible, presumably due to electrostatic repulsion between the negatively charged catalytically active bimolybdate species and the negatively charged aldonate product. The production of 2 and 3 is mediated by the formation of two structurally distinct bimolybdate complexes, one producing the gluco isomer and the other producing the manno isomer. Reaction byproducts were also observed, specifically d-[1-¹³C]arabinose (4 ¹) and [¹³C]formate (5), when 1 ¹ was used as the reactant. These byproducts appear to form from the breakdown of bimolybdate complexes via alternative pathways that compete with those responsible for aldonate formation.