Iron-catalyzed carboarylation of alkynes via activation of π-activated alcohols: rapid synthesis of substituted benzofused six-membered heterocycles

Abstract

An Fe(OTf)3-catalysed carboarylation of alkynes is reported to the straightforward synthesis of densely substituted 1,2-dihydroquinolines from N-propargyl anilides and π-activated alcohols. The reaction provides a new method for the synthesis...

Substrate‐Controlled Product Divergence in Iron(III)‐Catalyzed Reactions of Propargylic Alcohols: Easy Access to Spiro‐indenyl 1,4‐Benzoxazines and 2‐(2,2‐Diarylvinyl)quinoxalines

“…In path I (X=O), FeCl 3 acting like a Lewis acid [20,21b] affords a benzylic carbocation intermediate D which isomerizes into bicyclo[3.1.0]epoxonium ion E through intramolecular nucleophilic addition of oxygen onto the transient carbenium ion adjacent to the NTs group [23] . Species E is now poised to undergo intramolecular Fridel–Crafts (IMFC)‐type cyclization [20a,24] preferably by 5‐ exo epoxide‐ring opening (as depicted in Scheme 2) which is consistent with Baldwin's rule [23b] and the prediction made in a recent study [23a] following experimental and computational evidences. Next, aromatization by deprotonation followed by demetalation [20b–c] affords the product 3 along with regeneration of FeCl 3 which enters into the catalytic cycle.…”

“…Based on our experimental results and known iron(III) chemistry, [20] a plausible reaction mechanism is proposed (Scheme 2). At first, the alcohol group of the substrate 1/2 is activated (species A ) through co‐ordination with Fe III ‐catalyst leading to the generation of a transient propargylic carbocation B [20a] . Next, species B undergoes intramolecular nucleophilic attack by the tethered NHTs group to generate an allenic intermediate 3’ (X=O)/ 4’ (X=NTs) [21a] which forms a complex [20b–c,21b] with FeCl 3 (species C ) to give rise to the product [22] 3 / 4 following pathway I or II as described below.…”

“…This triggers the formation [25] of intermediate E ’ with concurrent release of p ‐TsOH and a proton that helps the demetallation [20b–c] of E ’ to furnish the intermediate F ’. Finally, subsequent 1,2‐elimination from F ’ with the assistance of FeCl 3 (as depicted in Scheme 2) would give rise to the product 4 and form FeCl 2 Ts [20a] and HCl which may further react among themselves to regenerate the Fe III catalyst.…”

DDQ/Fe(NO3)3-Catalyzed Aerobic Synthesis of 3-Acyl Indoles and an In Silico Study for the Binding Affinity of N-Tosyl-3-acyl Indoles toward RdRp against SARS-CoV-2

“…By virtue of their ubiquitous nature and broad-spectrum appearance in natural and synthetic bioactive compounds and pharmaceutical ingredients, nitrogen heterocycles form an important class of compounds . Providing more emphasis, indoles and their 3-substituted derivatives are always in the center of research because of their widespread applications in pharmaceuticals as potential drug candidates and in the discovery and development of novel functional materials. , In particular, synthesis of 3-acyl indoles has drawn the immense attention of organic synthetic chemists because of their relevance in natural products and pharmaceutical entities and their capability of binding with many biological receptors to show potential anti-tumor, antiviral, and anti-carcinogenic activity (Figure ), and so forth .…”

Cascade Cyclization of Azadienes with Difluoroenoxysilanes: A One-Pot Formal [4 + 2] Approach to Fluorinated Polyfused Heterocycles

“…On the basis of the understanding of the designed reaction process, we investigated the cascade reaction of azadiene 1a and difluoroenoxysilane 2a by employing the Lewis acids (FeCl 3 , Fe­(OTf) 3 , Cu­(OTf) 2 , and In­(OTf) 3 ) that have the ability to both construct the fluorinated C–C bond and remove the N -tosyl ( N -Ts) protecting group (Table , entries 1–4). However, disappointingly, the desired fluorinated benzofuro­[3,2- b ]­pyridine product 3a could be obtained in yields up to only 21% when Cu­(OTf) 2 (2.0 equiv) was used (entry 3).…”