Synthesis of C2-symmetric bis-indolyl sulfones

A new class of C2-symmetric bis-indole derivatives with 2,2′-linkage has been synthesized from bis-propargyl sulfones. The method involves treatment of the sulfones with catalytic amount of triethylamine to form the indole derivatives presumably via the intramolecular Michael addition to the intermediate bis-allenic sulfones. Interestingly, the expected Garratt-Braverman pathway was not followed.