Sodium-mediated magnesiation of thiophene and tetrahydrothiophene: structural contrasts with furan and tetrahydrofuran

Sulfur-containing heterocycles are currently attracting a great deal of interest in several diverse fields. For instance, substituted tetrahydrothiophenes[1] have received considerable attention due to their extremely wide-ranging chemical and biological applications.[2] These include their use as potent a-glucosidase inhibitors,[3] as an inhibitor of copper amine oxidases[4] and as selective A3 agonists and antagonists.[5] In addition, they have been utilised in chemical transformations, such as catalytic asymmetric epoxidation, catalytic intramolecular cyclopropanation, and asymmetric metal catalysis hydrogenation.[6] From a nanochemical perspective, the adsorption chemistries and physical properties of various thiophenes and tetrahydrothiophenes on gold surfaces have recently come to the fore.[7] Polythiophenes are also key compounds in modern materials research, currently utilised in, for example, the fabrication of semi-conducting, fluorescent, and electronic and optoelectronic materials.[8]In this work, metallation (exchange of a hydrogen atom with a metal atom) of the parent heterocycles, tetrahydrothiophene (THT) and thiophene is considered. Metallation is one of the most fundamental reactions in modern day synthesis and is a key tool in the preparation of functionalised aromatic and heterocyclic compounds. It is usually achieved by the utilisation of commercially accessible organolithiums (or lithium amides); however, these reactions do have their drawbacks, including the intolerance of certain functional groups, the need for cryoscopic temperatures and the inadvertent reactivity with polar reaction solvents.