In situ Generated Reagent from Sulfur for Alkynylanthraquinone Cyclization. The Simple Synthesis of Angular Thienoanthraquinones.

Abstract A new strategy for thiophene ring formation via the direct C H cyclization of 1-alkynyl-9,10-anthra(4-alkynyl-1-aza-9,10-anthra)quinones to give the corresponding thienoanthraquinones has been developed. A highly effective sulfinating agent was generated in situ by the reaction of elemental sulfur and alkali. It was also shown that this reagent is effective in the cyclization reaction with replacement of the chlorine atom.