3‑Alkenylation or 3‑Alkylation of Indole with Propargylic Alcohols: Construction of 3,4-Dihydrocyclopenta[<i>b</i>]indole and 1,4-Dihydrocyclopenta[<i>b</i>]indole in the Presence of Different Catalysts

Abstract

3-Alkenylation or 3-alkylation of indole with propargylic alcohols could be efficiently controlled by the catalyst. In the presence of triflic acid, 3-alkenylation of indole occurred and a 3,4-dihydrocyclopenta­[<i>b</i>]­indole skeleton was effectively constructed in moderate to excellent yields via a cascade process. In the presence of Cu­(OTf)_2, 3-alkylation of indole resulted in the formation of 3-propargylic indole, which could be further converted into 2-iodo-1,4-dihydrocyclopenta­[<i>b</i>]­indoles in the presence of <i>N</i>-iodosuccinimide and boron trifluoride etherate. Possible mechanisms related to the 3-alkenylation or 3-alkylation of indole and their extension to the formation of 3,4-dihydrocyclopenta­[<i>b</i>]­indoles or 1,4-dihydrocyclopenta­[<i>b</i>]­indoles are postulated and discussed