Diols, deoxy dehydration

Deoxy-D-glycero-hexo-2,3-diulose is a typical product of degradation and 4-0-substituted derivatives of fructose (e.g. lactulose, which arises by isomerisation of lactose). 1,2-Enolisation of 4-deoxy-D-g lycero-hexo-2,3-diulose yields, via the appropriate l-ene-l,2-diol, unstable 4-deoxyhexos-3-ulose, which splits into formic acid and 1,2-enediol of 3-deoxy-D-glycero-pentulose in neutral or alkaline solutions by a reverse Claisen condensation mechanism. This sugar can be oxidised to 3-deoxy-D-glycero-pentos-2-ulose or may dehydrate to form 3,4-dideoxypentosulose (Figure 4.32). Other reaction products are isosaccharinic acids. 

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