Synthesis of Polysubstituted Cyclopentene and Cyclopenta[b]carbazole Analogues from Unsymmetrical 4-Arylidene-3,6-diarylhex-2-en-5-ynal and Indole Derivatives via an Iodine Mediated Electrocyclization Reaction

An efficient method for the synthesis of polysubstituted cyclopentene and cyclopenta[b]carbazole derivatives through the iodine-promoted electrocyclization of substituted indoles and 4-arylidene-3,6-diarylhex-2-en-5-ynal derivatives is reported. Polysubstituted cyclopentene derivatives were produced through 4 pi electrocyclization reactions with indole, 7-methylindole, and 5-bromoindole as coupling partners, whereas cyclopenta[b]carbazole derivatives were produced via 6 pi electrocyclization in the case of methoxy (-OMe)-substituted indoles. The methods reported herein diastereo- and regioselectively proceed under straightforward and mild conditions.