Approaches to benzo[b]thiophenes by gas-phase pyrolysis of methyl 2-(alkylthio)cinnamates

Abstract

Flash vacuum pyrolysis (FVP) of 3-[2-(t-butylthio)phenyl]propenoate 7 at 700 °C (0.01 Torr) unexpectedly gave a mixture of benzo[b]thiophene derivatives 5 (15%) and 8 (21%), and thiocoumarin 9 (28%). Control experiments show that thiophenoxyls (e.g. 15) cyclise efficiently to benzo [b]thiophene 5 under similar conditions. It follows that FVP of S-t-butyl derivatives of thiophenols, is not an efficient means of generating thiophenoxyl radicals owing to competing hydrogen capture processes.

Formation of dibenzofurans by flash vacuum pyrolysis of aryl 2-(allyloxy)benzoates and related reactions

“…Yields were variable (see Experimental section and ESI †) but no attempt was made to optimise the formation of these precursors. Substituents were chosen to provide a range of 2-, 3-and 4-substituted aryl esters and, in one case (7), a substrate with a further substituent on the salicylate ring was synthesised (see below).…”

Novel Route to 2,3-Substituted Benzo[b]thiophenes via Intramolecular Radical Cyclization

“…Emergence of such promising chemotherapeutic agents has stimulated new investigations into the concise synthesis of 2,3-substituted benzo[ b ]thiophenes. , The 2-arylbenzo[ b ]thiophenes are usually synthesized by multistep intramolecular cyclization of thiophenol derivatives developed by Kost and other workers. , However, these methods usually required both acidic and/or basic conditions, proved to be nonregioselective, , and were not compatible with acid- and base-sensitive functional groups. Therefore, other methods have been developed starting from thiobenzyls or thioanisole derivatives along with useful catalytic routes via direct Heck type arylation of 2-unsubstituted benzo[ b ]thiophenes − and iodine-induced intramolecular oxidative cyclization of o -acetylenic thiobenzyl derivatives. , …”