L-Methoxyindole-3-carbaldehyde

These types of compounds are expected to be produced by utilizing nucleophile substitution reaction at the 2 position of l-methoxyindole-3-carbaldehyde (115a) and 3-acetyl-1-methoxyindole (107). In practice, after conversion of 115a to 195a (53%) as described in Section IV.J, 195a is allowed to react with various amines. Consequently, many derivatives of 271 are obtained. Typical examples (271a-c) are shown in the scheme (99H1157). 

Thallation of l-methoxyindole-3-carbaldehyde with thallium trisfluo-roacetate followed by treatment with potassium iodide gave the 4-iodo derivative in 91% yield, and this has been converted into many other 1-methoxyindole derivatives (86CPB677). When the thallated indole reacted with methyl acrylate in the presence of a catalytic quantity of pal-ladium(ll) acetate, 47% of the product was the 4-derivative 160, but 11% of the 5-isomer was also formed (86CPB4116). 

Phytoalexin is also an interesting compound. The plant family, Cruciferae, utilizes 1-methoxyindole compounds as phytoalexins. We expected there was a chance to find new agrochemicals among analogs of l-methoxyindole-3-carbaldehyde [52] (10a, daikon-phytoalexin [53]). So, we have thus far prepared a lot of related compounds. Some of them are 5a,b, 6a-f, 10b, 119, 206a-d, 207a,b, and 208a,b. These are found to have mild activities (Somei and co-workers, personal communication, 2006). 

Methoxyindole-3-carbaldehyde (10a) undergoes nucleophilic substitution reactions in sharp contrast with indole-3-carbaldehyde that does not react with nucleophiles under forcing reaction conditions. The most reactive reactant among the thus-far obtained l-hydroxy and 1-methoxy derivatives is l-methoxy-6-nitroindole-3-carbaldehyde (10b) as shown in Fig. 2. So, the nudeophihc substitution reactions of 10b in DMF are examined for the synthesis of new 2,3,6-trisubstituted indoles. The representative results are shown in Scheme 14 [13]. 

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