Catalytic [2+2+1] Synthesis of Fused Thiophenes Using Thiocarbonyls as Sulfur Donors

Abstract

The use of N-(p-chlorophenyl)methylbenzoxazole-2-thione as a sulfur-atom donor enables the catalytic [2+2+1] cycloaddition of diynes in wet DMF at 80 °C when open to air, thus affording diverse fused thiophenes with good yields and wide functional-group compatibility. A plausible mechanism, involving a cationic ruthenacycle intermediate, was also proposed on the basis of several control experiments.