Catalysis of Elemental Selenium and Tellurium in the Formation of Thiophene Derivatives from Alkyne and Elemental Sulfur

Abstract

Elemental selenium and tellurium were found to catalyze the formation of thiophene derivatives in the reaction of elemental sulfur with alkyne (dimethyl acetylenedicarboxylate [1 a] and diphenylacetylene [1 b]). In the reaction of 100 mmol of [1 a] with 40 mmol of S at 110°C for 24 h in the absence of selenium or tellurium, the yield of tetramethyl 2, 3, 4, 5-thiophenetetracarboxylate [2 a] was 5%, while the yields of [2 a] in the presence of 0.04, 0.48, and 4.0 mmol of Se were 22, 39, and 53%, respectively. Elemental tellurium acted as a catalyst. In the similar conditions the yield of [2 a] in the presence of 0.2 mmol of Te was 38%.
In the thi ophene forming reaction catalyzed by (η-cyclopentadienyl) (1, 5-cyclooctadiene)cobalt(I) [4], elemental selenium promoted the reaction. The yield of [2 a] was 75%in the reaction of 100 mmol of [1 a] with 40 mmol of S at 110°C for 24 h in the presence of 0.2 mmol of [4] and 40 mmol of Se.
In the reaction of [1 b] p (25 mmol) with S (10 mmol) at 140°C for 24 h, the presence of 10 mmol of Se increased the yield of 2, 3, 4, 5-tetraphenylthiophene from 2% (in the absence of Se) to 10%.