Condensed thiophen ring systems. Part IV. Synthesis, reactions, and stability of 2-phenyl-3-benzo[b]thienyl-lithium and related compounds

Abstract

2-Phenylbenzo[b]thiophen and its 5-methyl-, 5-chloro-, and 5-bromo-derivative were brominated at the 3-position and each of the resulting 3-bromo-derivatives was treated with n-butyl-lithium in ether at –70° to give the corresponding 3-lithium compound. These reacted with carbon dioxide to give, after hydrolysis, varying yields of the corresponding acids and with NN-dimethylformamide to give the corresponding aldehydes (40–55% yields). With dimethyl sulphate 2-phenyl-3-benzo[b]-thienyl-lithium gave a high yield of 3-methyl-2-phenylbenzo[b]thiophen. When an ethereal solution of 2-phenyl-3-benzo[b]thienyl-lithium was prepared at –70° and then allowed to stir at room temperature for 18 hr. prior to hydrolysis, it gave a mixture of 2-phenylbenzo[b]thiophen (30·5%) and phenyl-o-(n-butylthio) phenylacetylene (61%). The other 3-benzo[b]thienyl-lithium compounds behaved similarly.