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

Abstract

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 4π electrocyclization reactions with indole, 7-methylindole, and 5-bromoindole as coupling partners, whereas cyclopenta­[b]­carbazole derivatives were produced via 6π electrocyclization in the case of methoxy (−OMe)-substituted indoles. The methods reported herein diastereo- and regioselectively proceed under straightforward and mild conditions.

Iodine‐Catalyzed Cascade Reaction of 2‐Styrylbenzaldehydes with Indoles in the Synthesis of 1H‐Indenes via 4π‐Electrocyclization

“…Examples of [4+2] annulation strategies have been reported for the generation of a variety of carbazole derivatives [15a,b] . Iodine‐promoted electrocyclization of 4‐arylhex‐2‐en‐5‐ynals initiated by a nucleophilic addition using indole has been reported [15c] . This reaction offers either polysubstituted cyclopentene derivatives or cyclopenta[ b ]carbazoles depending on the nature of the indole derivatives.…”

Recent Studies of Bifunctionalization of Simple Indoles

“…The Yao group [7i] reported the I 2 ‐promoted tandem cyclization between indoles and 4‐benzylidene‐3,6‐diphenylhex‐2‐en‐5‐ynals. Firstly, Friedel‐Crafts reactions of aldehydes with highly electron‐rich part of indoles at C‐3 achieved the formation of secondary alcohols, which then led to carbocation intermediates.…”