1977 年 97 巻 3 号 p. 223-230
The products from the positive Voges-Proskauer reaction namely, the reactions of 1-phenylpropane-1, 2-dione (PPD) with 1, 1-pentamethyleneguanidine (PMG), and those from the negative Voges-Proskauer reaction, namely the reactions of benzil with PMG, PPD with benzamidine, and of benzil with benzamidine were isolated, and the relation between the structural difference in these products and their color developments was elucidated. The reaction of PMG with PPD afforded 4-hydroxy-4-methyl-5-phenyl-2-piperidino-4H-imidazole [Ic], which is known as the intermediate in the Voges-Proskauer reaction. The reactions of PMG with benzil, benzamidine with PPD, and benzamidine with benzil afforded 2, 4, 4/2, 5, 5-trisubstituted-2-imidazolin-4/5-one-s [II, IV, V] and 4-hydroxy-4, 5-diphenyl-2-piperidino-4H-imidazole [III], respectively. It was found that II, IV, and V were formed through the benzilic acid rearrangement, while the intramolecular rearrangement was not involved in the formation of III. II, IV, and V did not react to give any color development in the presence of alkali, but III which had a similar skeleton to that of Ic gave II with an intramolecular rearrangement. Since Ic gave the pigments (A, B, and C), whose structures were already elucidated, by the release of formaldehyde from 4-hydroxy and 4-methyl groups of 4H-imidazole or the reaction with 1-naphthol in the presence of alkali, this reaction process was found to be of importance for exhibiting the positive Voges-Proskauer reaction. A tautomerism was found between IV and V by examination of their IR spectra.