Synthesis of the So-called Dehydro-rotundinium Salt and Its Partial Reduction.
1962 年 10 巻 3 号 p. 191-200
詳細
1962 年 10 巻 3 号 p. 191-200
The proposed structure for rotundine and dihydro-rotundine by Matsuno was proved untenable. The synthesized so-called rac-dihydro-rotundine (II) was dehydrogenated with mercuric acetate in methanolic solution to give the product as well-defined quaternary salt (XII). This was more advantageously prepared by dehydrogenating 2-oxo-3-methyl-9, 10-dimethoxy-1, 2, 3, 4, 6, 7-hexahydro-11bH-benzo [a] quinolizine (IX), the intermediate for (II), with mercuric acetate in 10% acetic acid solution to produce a phenolic quaternary salt (X) and methylating the latter with dimethyl sulfate and an excess of conc. potassium hydroxide solution, giving (XIV). Natural dihydro-rotundine, prepared by reducing the natural alkaloid, gave a dehydro-quaternary salt by a similar method, but the product showed ultraviolet and infrared absorption spectra different from those of (XII). Partial hydrogenation experiments of (XII) and (XIV) under a variety of conditions failed to afford a compound having the diene system, as was proposed for natural rotundine. The products isolated were rac-dihydro-rotundine-type of compound, whose three isomers (II, XV, and XVI) were characterized. In conformity with their structure they smoothly gave the ketone (IX) when treated with dil. hydrochloric acid, whereas the natural dihydro-rotundine was proved to be quite stable to hydrochloric acid even at an elevated temperature. Similar experiments were also conducted with synthetic rac-dihydro-isorotundine (I).
