29 青葉アルコールの芳香環化反應

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In an earlier work, it was reported that leaf alcohol,when refluxed with metallic sodium, gave a lemone-like flavor, which was assumed as being 3-propyl-nona-3,6-dien-l-ol or 3-propyl-nona-3-en-l-ol. In this report, it was revealed that leaf alcohol resisted catalytic hydrogenation and faded neither KMnO_4 solution nor Br_2, contrary to what was expected from the aliphatic diene. Through chemical and physical means that it was given trimellic acid upon oxidation with KMnO_4 and (VI) was produced from (III-a) by the same condition with leaf alcohol,and then the UV-absorption at 268mμ and IR-absorption bands characteristic (1510, 889,832cm^<-1>) suggesed that it should be resulted a aromatic compound, this structure was deduced as 2-propyl-5-ethyl-benzylalcohol(IV). (IV) was also obtained from each of (I-b-d) and (I-e) under exactly the same reaction conditions. Furthermore, in the extention of this reaction to C_5;(II) and C_4;(III)-a,b), the aromatization was also effected 2-ethyl-5-methyl-(V) and 2-methyl-benzylalcohol(VI). This aromatization reaction originally found with leaf alcohol seemed to be generalized to the aliphatic αβ- and βγ-unsaturated alcohols and aldehyds, and hence was designated as leaf alcohol reaction. This reaction mechanism was proposed on the basis of reaction with (III-b) or (I-e) which on stepweise treatment with weaker bases gave (VI) or (IV) through isolating cyclodiene intermediate, (VIII-a) or (VIII-b). Conclusively, therefore, this mechanism involving dehydrogenation, Michael addition, aldol condensation-cyclization and dehydration, crossed Cannizzarro reaction is preferred to the previously proposed one.
天然有機化合物討論会の論文
1967-09-25

29 青葉アルコールの芳香環化反應

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