D-Hamamelose and Other 2-C- Hydroxymethyl pentoses

Addition of four equivalents of boric acid to the starting ketose improves the original 6.5% yield of D-hamamelose up to 20% [55]. Thus, the product of the molybdic acid catalyzed rearrangement, D-hamamelose, is apparently being removed from its thermodynamic equilibrium with D-fructose by a competitive complex formation with boric acid. 

In a similar manner, L-sorbose, on treatment with a catalytic amount of molybdic acid, equilibrates with its rearranged isomer, 2-C-(hydroxymethyl)-L-lyxose, again accompanied by a side product of a secondary process, L-fructose [55]. Analogous co-application of boric acid shifts in this case the thermodynamic yield of 2-C-(hydroxymethyl)-L-lyxose from 3 % to a preparatively more interesting 12 %. 

Molybdic acid catalyzed isomerization of D-tagatose (without boric acid) provided a 19 1 ratio (as estimated by NMR spectroscopy) of the ketose and 2-C-(hydroxymethyl)-D-xylose. Surprisingly, D-psicose on treatment with molybdic acid under otherwise identical reaction conditions, even after prolonged reaction times, did not lead to the formation of 2-C-(hydroxymethyl)-D-arabi-nose as expected. The co-application of boric acid, either in this case or in the case of D-tagatose, does not shift the equilibria towards the corresponding 2-C-hydroxymethyl)aldoses. 

Molybdic add catalyzed isomerization of D-tagatose (without boric add) provided a 19 1 ratio (as estimated by NMR spectroscopy) of the ketose and 2- 

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