Bismuth(III) Triflate Catalyzed Three-Component Reactions of Indoles, Ketones, and α-Bromoacetaldehyde Acetals Enable Indole-to-Carbazole Transformation

Abstract

A three-component reaction of indoles, α-bromoacetaldehyde acetals, and ketones was developed by using bismuth­(III) triflate as the catalyst to realize a straightforward approach for synthesizing carbazole derivatives. The reaction was established mechanistically through the autotandem catalysis of Bi­(OTf)3 in the following two steps: (i) Friedel–Crafts-type alkylation of indole with α-bromoacetaldehyde acetal, which produced a tryptaldehyde-type intermediate and (ii) [4 + 2] annulation of this intermediate with the ketone component.

Recent Studies of Bifunctionalization of Simple Indoles

“…In 2019, the Verma group [1m] reviewed the synthesis of carbazoles from indoles (2015–2019). The Gu group [4a,b] utilized α‐ bromoacetaldehyde acetal as the key reagent in the indole‐mediated benzo[ α ]carbazoles [4b] . During the Bi(OTf) 3 ‐catalyzed three‐component reactions[4a], the Friedel‐Crafts alkylation and hydrolysis generated aldehyde intermediates.…”

Clean Preparation of Quinolin-2-yl Substituted Ureas in Water

“…According to previous reports, the C2 position of quinoline N -oxides may be functionalized via a number of reaction processes, which include the C–H bond alkylation, − arylation, alkenylation, − acetoxylation, , sulfonylation, − amidation, − amination, − hydroxylation, , phosphonation, , and thiolation of quinoline N -oxides. However, to the best of our knowledge, the preparation of quinolin-2-yl substituted ureas from readily available quinoline N -oxides has never been reported.…”

Practical Approach for Clean Preparation of Z-β-Thiocyanate Alkenyl Esters

“…β-Thiocyanate alkenyl esters represent highly valuable multifunctional compounds because both alkenyl ester − and alkenyl thiocyanate − moieties are broadly utilized in various fields such as organic synthesis, pharmacy, and material science. Directly converting propargylic carboxylates into β-thiocyanate alkenyl esters through multicomponent reaction − represents a highly attractive transformation in organic synthesis, given the easily available raw materials. Recently, our group developed a novel method to synthesize various β-thiocyanate alkenyl esters in the range of 11–14:1 Z/E ratios from propargylic carboxylates via Brønsted acidic ionic liquid-catalyzed hydrothiocyanation of propargylic carboxylates .…”