Regiocontrolled Synthesis of Ring-Fused Thieno[2,3-c]pyrazoles through 1,3-Dipolar Cycloaddition of Nitrile Imines with Sulfur-Based Acetylenes

1,3-Dipolar cycloadditions of C-carboxymethyl-N-arylnitrile imines with substituted acetylenes bearing thiol or sulfone groups were studied. The sulfur controls the regiochemistry of the reaction, and this protocol was applied to the synthesis of ring-fused thieno[2,3-c]pyrazoles.