1960 年 80 巻 9 号 p. 1212-1217
The chalcone glycoside, prepared by ring cleavage of tetramethylastilbin, was heated with 10% pyridine water for a long period of time and afforded tetramethylastilbin and an amorphous substance which was assumed to contain chiefly tetramethylneoastilbin. Treatment of astilbin (I) with hot, conc. alkali solution is thought to cause initial ring cleavage to form the chalcone glycoside (XII) whose isolation is difficult. Similar to the case of isomerization of (I) by hot 10% pyridine water, neoastilbin (II), isoastilbin (III), and structurally unknown chalcone compound are isolated, besides (I), in this case. The spot corresponding to that of neoisoastilbin (III) was detected in the paper chromatogram of this product. Isomerization of (I), (II), (III), and (IV) is thought to be due mostly to inversion of the conformation of 3-OR (where R is L-rhamnosyl) by enolization of the carbonyl in the aglycone, as stated in the preceding peport, but it may be considered that the extremely unstable (XII) is an intermediate in this reaction and various isomers are formed during recyclization (cf. Chart 1).