Selective Formose Reaction under Microwave Irradiation

Abstract To realize sustainable societies, production of organic compounds, which is not based on fossil resources, should be developed. Thus, C1 chemistry, utilizing one-carbon compounds as starting materials, has been of increasing importance. In particular, formose reaction is promising because the reaction produces sugars (monosaccharides) from formaldehyde under basic conditions. On the other hand, since microwave (MW) induces the rotational motion of molecules, MW irradiation often improves the selectivity and efficiency of reactions. In this study, formose reaction under MW irradiation was thus investigated under various conditions. Formose reaction proceeded very fast and selectively using 1.0 mol kg− 1 formaldehyde and 55 mmol kg− 1 calcium hydroxide (Ca(OH)2) as a catalyst at a high set temperature (150°C) for a short time (1 min). The major products, i.e., hexose and heptose, were isolated by thin layer chromatography and characterized by NMR and mass spectroscopy. These characterization data elucidated that the hexose and heptose were 2-hydroxymethyl-1,2,4,5-tetrahydroxy-3-pentanone (C6*) and 2,4-bis(hydroxymethyl)-1,2,4,5-tetrahydroxy-3-pentanone (C7*), respectively. On the basis of these observations as well as density functional theory calculations, a plausible reaction pathway was also discussed; Once 1,3-dihydroxyacetone is formed, consecutive aldol reactions favorably occur to form C6* and C7*. This study should provide significant insights not only for production of organic compounds not based on fossil resources but also for the sugar formation under prebiotic conditions.