Indole Compounds. VI. Syntheses of Indole Thioethers by Direct Cyclization of Phenylhydrazine Hydrochlorides and Aliphatic Acetals Under Mild Conditions

The ease of Fischer indolization, into several types of indole thioethers, with respect to the nature of the starting arylhydrazine and acetal components in 25°/o acetic acid at 80° is investigated. 3-Benzyloxy- and 3,4-dimethyl-phenylhydrazine hydrochlorides indolize with 4-benzylthiobutanal diethyl acetal into isomeric mixtures of 4- and 6-benzyloxy-, and 4,5- and 5,6-dimethyl-3- (2-benzylthioethyl) indoles (I and II, and III and IV, respectively); separation and structure assignment of the isomers is reported. Debenzylation of III and IV gives the corresponding 3-(2-mecaptoethyl)- and bis[3-(2-thioethyl)indoles]. Indolization of 3-benzylthiopropanal diethyl acetal with several arylhydrazine hydrochlorides results in the formation of the corresponding 3-benzylthiomethylindoles in low yield; a subsequent decomposition of the products under the conditions of the indolization reaction has been established. 4-Benzylthiophenylhydrazine hydrochloride and 4-aminobutanal diethyl acetal cyclize smoothly into 5-benzylthiotryptamine hydrochloride