This Thesis is a report of an investigation into the preparation of thionaphthen isosteres of biologically active indole compounds . The introduction deals with the theoretical implications of the various approaches to the syntheses of biologically active compounds, and in particular those with an indole nucleus present in the molecule. A review on "Biological Activity in Compounds Possessing Thiophen Rings" is included, and justification is provided for the preparation of thionaphthen isosteres of such compounds as 5-hydroxytryptamine. In section 1, the position of electrophilic substitution in 5-substituted thionaphthens was investigated with a view to employing the various protecting groups in a synthesis of the thionaphthen analogue of 5-hydroxy-tryptamine. Other interesting orientation effects are also reported. Section 2 deals with the preparation of various thionaphthen derivatives containing a gramine side-chain as possible antagonists of adrenaline and of 5-hydroxy-tryptamine. In section 3, attempts to prepare 3-(2'-amino ethyl)-5-hydroxythionaphthen, the thionaphthen analogue of 5-hydroxytryptamine, are reported. Various other isosteres of hydroxtrytryptamine-like compounds including 3-(2'-amino ethyl)-6-hydroxy-thionaphthen are reported. Section also deals with the syntheses of thionsphthen analogues of harmine and harmaline
