Acid-catalysed reaction of D-glucose with benzaldehyde produces the 4,6- O -benzylidene derivative. Reduction with NaBH₄ , followed by excess HIO₄ cleavage and acid hydrolysis, yields a C₄H₈O₄ tetrose and benzaldehyde. What is the configuration of this tetrose?

Step-by-step solution

The reaction sequence proceeds as follows: 1. Protection: The acid-catalysed reaction of D-glucose with benzaldehyde selectively protects the hydroxyl groups at C4 and C6, forming 4,6- O -benzylidene-D-glucopyranose. 2. Reduction: Treatment with NaBH₄ reduces the hemiacetal (anomeric C1 carbon) to a primary alcohol, opening the ring to form 4,6- O -benzylidene-D-glucitol. In this molecule, the free hydroxyl groups are located at C1, C2, C3, and C5. 3. Oxidative Cleavage: Excess HIO₄ cleaves vicinal diols. The conti