Action of Molybdate Anion on <scp>d</scp>-Glucosone: Catalytic Conversion to Aldonates Involving C1–C2 Transposition

Treatment of the osone (aldos-2-ulose), d-[1-¹³C]glucosone (<b>1</b> ¹), with sodium molybdate at 90° for 30 h gave a mixture of d-[2-¹³C]gluconate (<b>2</b> ²) and d-[2-¹³C]mannonate (<b>3</b> 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 <b>1</b> confirmed this transposition. In contrast to the aldose reaction, the reaction with <b>1</b> is irreversible, presumably due to electrostatic repulsion between the negatively charged catalytically active bimolybdate species and the negatively charged aldonate product. The production of <b>2</b> and <b>3</b> is mediated by the formation of two structurally distinct bimolybdate complexes, one producing the <i>gluco</i> isomer and the other producing the <i>manno</i> isomer. Reaction byproducts were also observed, specifically d-[1-¹³C]arabinose (<b>4</b> ¹) and [¹³C]formate (<b>5</b>), when <b>1</b> 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.