Chapter 5.1 Five-membered ring systems: Thiophenes & Se, Te analogs

This chapter describes five-membered ring systems. The synthesis and chemistry (reactions) of thiophenes, benzothiophenes, and related selenium and tellurium ring systems that has been reported during the past year is the subject of this chapter. Aspects of thiophene chemistry have been reviewed during the past year including transition metal-catalyzed reactions and the synthesis and structure of thiophene 1,1-oxides and related compounds. The relative aromaticity of numerous heterocyclic compounds are explored quantitatively while theoretical calculations for n-stacking between thiophene rings has been investigated to further define the intermolecular interactions between thiophene oligomers and polymers. Treatment of 1,4-dicarbonyl compounds with Lawesson's reagent is a common method of de novo thiophene synthesis and was recently applied to the preparation of thienoazepines. A novel preparation of 2,5-disubstituted thiophenes involved the treatment of 3,5-dihydro-1,2-dioxins prepared by photo-oxidation of the corresponding dienes with Lawesson's reagent. Treatment of 1,4-dilithiated dienes with various sulfur transfer reagents including sulfur, benzenesulfonic acid thianhydride, and carbon disulfide provided methods for the preparation of thiophene derivatives.