2-Indolymethanols as 4-atom-synthons in oxa-Michael reaction cascade: access to tetracyclic indoles

Abstract

TThe first Brønsted acid-catalyzed oxa-Michael reaction cascade of 2-indolylmethanols with trione alkenes was accomplished. By using this practical approach, a variety of tetracyclic indoles were readily created in ordered sequence...

Catalyst-free racemic and H2O/CPA-catalyzed asymmetric regio-reversed domino processes of triketone enones with azlactones

“…Based on the current experimental results and previous reports, 5 a ,7 plausible reaction pathways were suggested (Scheme 5). The enolization of azlactone 2a afforded its active form.…”

“…6 Recently, we accomplished the Brønsted acid-catalyzed oxa-Michael reaction cascade of triketone enones with 2-indolylmethanols for the construction of tetracyclic indoles, and found that the chemoselectivity could be reversed by employing different Brønsted acids. 7 Along this line, we questioned whether the regio-reversed domino process of triketone enones would be feasible and if the stereoselectivity could be simultaneously controlled. Herein, we report the reaction cascade of triketone enones with azlactones (Scheme 1c).…”

“…found that the chemoselectivity could be reversed by employing different Brønsted acids. 7 Along this line, we questioned whether the regio-reversed domino process of triketone enones would be feasible and if the stereoselectivity could be simultaneously controlled. Herein, we report the reaction cascade of triketone enones with azlactones (Scheme 1c).…”

Utilizing Graphene Oxide (GO) Catalysed Cascade in the Synthesis of Tetracyclic Pyrano[3,4‐b]indole Derivatives

“…The electron density plays an important role in intramolecular Friedel–Crafts cyclization step and the electron‐donating group has the ability to increase the electron density of the indole ring, which enhances the rate of the intramolecular cyclization. The relative stereochemistry of the newly generated stereocenters was assigned by comparison of the NMR with that reported in the literature [5j] …”

“…In 2021 Mie et al . constructed [5j] dihyropyranoindoles from 2‐indolylmethanol and trione alkene in presence of strong Brønsted acid (PhO) 2 OPOH. However, they metioned that only strong acid e. g. (PhO) 2 OPOH, TFA, TsOH, MsOH etc.…”