39 The advanced Fischer Indolization of 2-Methoxyphenylhydrazonesを用いた天然産6-置換インドール類の合成

概要

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Fischer indolization of ethyl pyruvate 2-methoxyphenylhydrazone (1) gave unpredictable ethyl 6-chloroindole-2-carboxylate (2) as a main product instead of the expected ethyl 7-methoxyindole-2-carboxylate (4) in Fischer sence. On the other hand, treatment of the same hydrazone (1) with ZnCl_2 afforded another unexpected ethyl 5-chloroindole-2-carboxylate (9). These formations of abnormal indole products can be rationalized by the mechanism shown in Scheme 4. As an expanded application, we succeeded in developing these unexpected results to a synthetic method for indole derivatives having a unique carbon side chain at C_6. Treatment of 1 with TsOH in the presence of an excess amount of ethyl acetoacetate gave the indole product (13) possessing ethyl acetoacetate residue at C_6. We aimed at and succeeded in synthesizing the naturally occurring 6-(3-methylbuta-1,3-dienyl)indole (19) and 6-(3-methyl-2-butenyl)indole (27) from the above 13 through the synthetic routes in Scheme 6 and 7, respectively.
天然有機化合物討論会の論文
1973-10-01