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The experimental optical rotation (OR), electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectra of (R)-3-hydroxy-4,5-dimethylfuran-2(5H)-one (sotolon, 1) and (R)-5-ethyl-3-hydroxy-4-methylfuran-2(5H)-one (maple furanone, 2) taken in chloroform were compared to their spectra calculated with time-dependent density functional theory (TDDFT). Sotolon was shown to exist as a dimer in chloroform while maple furanone remains a monomer. Transition state barriers for the enol/keto tautomerization of sotolon were calculated and found to be high. The VCD method offers promise to ultimately distinguish between the presence of monomers or dimers.

This study constructed the relationship between l -amino acids and four-carbon d -sugar using quantum theory. Theoretically, an l -amino acid could react with the ketone to afford the corresponding Schiff base which may take place an Aldol reaction with a molecule of formaldehyde. An assumption is proposed that the Aldol addition products with ( R ) or ( S ) configuration could have different quantity due to the effect from stereogenic center of l -amino acid. By hydrolysis of the Aldol addition, different d - or l -sugar would form. Thus, B3LYP, WP1MPW91 and wB97XD theories were used for the energy difference computations at the 6-311++G(2d,p) level in the gas phase, or in water using PCM and SMD model, respectively. The predicted ee value sequence agrees well to the experimental result in the asymmetric synthesis of 3-carbon sugar using five l -amino acids. Further theoretical study exhibited that 4-carbon D sugar should form if the corresponding l -amino acid is used. The ee values of the 4-carbon sugar are bigger than those of 3-carbon d -sugars catalyzed by the same l -amino acids. This looks like the chiral amplification in the procedure.