GB938903A - Improvements in or relating to substituted indoles - Google Patents

Abstract

The invention comprises compounds having the general formula <FORM:0938903/IV(a)/1> wherein R represents an alkyl radical containing 1 to 4 carbon atoms, or an aralkyl radical containing 7 to 10 carbon atoms, and R1 represents an alkyl radical containing 1 to 4 carbon atoms, or a benzyl radical. The invention also comprises a process for preparing the compounds of formula I wherein a compound of general formula <FORM:0938903/IV(a)/2> is decarboxylated, and a process for preparing the compounds of formula Ia wherein a compound of formula I is alkylated with an alkylating agent containing 1 to 4 carbon atoms or benzylated with a benzyl halide. The indole-2-carboxylic acids mentioned above can be prepared from an appropriate 2-nitro-6-alkyl (or aralkyl) thio-toluene in the following manner:-the substituted toluene is condensed with a dialkyl oxalate in the presence of an alkali metal alcoholate to form an alkali metal enolate derivative of a substituted phenylpyruvic ester which is saponified to the corresponding phenylpyruvic acid whereupon the required indole-2-carboxylic acid compound is obtained by cyclising in the presence of sodium dithionite (Na2S2O4) or ferrous hydroxide. Alternatively, in the above process, the phenylpyruvic ester enolate may first be cyclised and then saponified to yield the required indole -2-carboxylic acid. The substituted toluenes used as starting material can be obtained by diazotising 2-nitro-6-amino-toluene, and reacting the product with an appropriate mercaptan. In Example 1, 2-nitro-6-amino-toluene is diazotised, and then reacted with methyl mercaptan in the presence of copper bronze giving 2-nitro-6-methylthio-toluene which after treatment with diethyl oxalate and potassium ethylate in ether, and subsequent saponification yields (2-nitro-6-methylthio-phenyl-pyruvic acid on acidification. The product when treated with sodium dithionite and sodium hydroxide, and then acidified yields 4-methylthio-indole-2-carboxylic acid which heated under reduced pressure at 260-270 DEG C. and then distilled gives 4-methylthio-indole. In Example 2, 4-benzylthio-indole is obtained by treating diazotised 2-nitro-6-amino-toluene with benzyl mercaptan, and then proceeding in a manner analogous to that described in Example 1. 1-Methyl-4-benzylthio-indole is obtained by treating 4-benzylthio-indole with methyl iodide and potassium amide; 1-benzyl-4-benzylthio-indole is similarly obtained using benzyl bromide instead of methyl iodide. The 4-alkylthio (or aralkylthio)-indoles may be used as odoriferous substances, as intermediates in the production of indole compounds, and for attracting or repelling insects.