Electrocyclization of Pyrroles

A variation of indole synthesis involving intermolecular Diels-Alder reactions of vinylpyrroles (Chapter 60) is mtramolecular electrocyclization reactions of vinyl- and divinylpyrroles to give indoles. 

Indole Ring Synthesis From Natural Products to Drug Discovery, First Edition. Gordon W. Gribble. 2016 John Wiley Sons, Ltd. Published 2016 by John Wiley Sons, Ltd. 

Funk and Huntley converted divinylpyrrolidine 10 to diene 11, and thence to an indole precursor 12 of )-cis-trikentrin B. A similar sequence was used to synthesize ( )-ci5 -trikentrin B. Dihydropyrrole 10 was assembled in five steps from A-Boc-2-pyrrolidinone. Fiirstner and coworkers synthesized several pyrrolo[2,3-c]carbazole alkaloids, the dictyodendrins B, C, and E, that featured a photochemical 6it-elecirocyclization and in situ dehydrogenation (equation 2) [21], Danheiser and colleagues effected an intramolecular benzyne generation and cycloaddition onto an alkynylpyrrole to afford a polycyclic indole (equation 3) [22], 

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