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Access to Indoles via Diels–Alder Reactions of 5‐Methylthio‐2‐vinylpyrroles with Maleimides
Author(s) -
Noland Wayland E.,
Lanzatella Nicholas P.,
Dickson Rozalin R.,
Messner Mary E.,
Nguyen Huy H.
Publication year - 2013
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.1571
Subject(s) - chemistry , diels–alder reaction , organic chemistry , combinatorial chemistry , catalysis
Diels–Alder reactions of 5‐methylthio‐2‐vinyl‐1 H ‐pyrroles with maleimides followed by isomerization gave tetrahydroindoles in moderate to good yield. Aromatization using activated MnO 2 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.