Access to indoles via Diels-Alder reactions of 5-methylthio-2-vinylpyrroles with maleimides

Wayland E Noland, Nicholas P. Lanzatella, Rozalin R. Dickson, Mary E. Messner, Huy H. Nguyen

Research output: Contribution to journalArticlepeer-review

5 Scopus citations

Abstract

Diels-Alder reactions of 5-methylthio-2-vinyl-1H-pyrroles with maleimides followed by isomerization gave tetrahydroindoles in moderate to good yield. Aromatization using activated MnO2 in refluxing toluene gave the corresponding 2-methylthioindoles in good yields, and demethylthioation using Raney nickel gave the 2-H indoles in excellent yields. The protection of the adducts produced aromatization in improved yield, demonstrating the effectiveness of the methylthio group as a protecting group for pyrroles; however, 5-methylthio-2-vinylpyrrole was shown to perform with slightly less efficiency than 2-vinylpyrrole in Diels-Alder reactions, indicating the protective group was more deactivating than desired. This route toward indoles offers high convergency and conveniently available starting materials that are easily purified. Bis-methylthioated vinylpyrroles were shown to have potential as highly activated Diels-Alder dienes.

Original languageEnglish (US)
Pages (from-to)795-808
Number of pages14
JournalJournal of Heterocyclic Chemistry
Volume50
Issue number4
DOIs
StatePublished - Jul 1 2013

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