Thiophenes and their Benzo Derivatives: Reactivity

Abstract

This chapter records the progress in mapping the reactivity of thiophenes, benzothiophenes, and dibenzothiophene since 1996. The three major areas of focus are (1) the design and synthesis of dithienylethene molecules for application as photochromic systems; (2) reactions of thiophenes brought about under transition metal catalysis; and (3) the synthesis, characterization, and reactivity of a plethora of transition metal complexes of thiophenes. Apart from these, several other interesting and, in some cases, surprising results have been discussed. These include 2,3- and 2,5-didehydrothiophenes, the generation of a stable radical cation of thiophene in solution and of stable crystalline salts of the dications of oligothiophenes; evidence for the formation of unusually stable thiophene radical anions during electrochemical reactions at cathodes; ring-opening reactions of thiophenes initiated by nucleophilic attack on the sulfur; and episulfidation of strained olefins by means of thiophene-derived sulfur-transfer reagents. In all the other familiar reactions of thiophenic substrates, only the more significant or novel results have been highlighted. The chapter also includes a brief survey of the reactivity of thiophene derivatives in which the aromaticity of the ring is lost; this includes a discussion of the newer developments in the chemistry of dihydro- and tetrahydrothiophenes, thiophene 1-oxides, and thiophene 1,1-dioxides, as well as those of 1-imino-, 1,1-diimino-, and 1-imino-1-oxo- derivatives of thiophenes.