Silver-Promoted Coupling of Carbon Dioxide,o-Alkynylanilines and Diaryliodonium Salts: Straightforward Access to 4-Aryloxy-2-quinolinones

Abstract

A silver-promoted three-component reaction of carbon dioxide, o-alkynylanilines and diaryliodonium salts using 1,4-diazabicyclo[2.2.2]octane (DABCO) as the base has been developed for the first time, which provides an efficient and straightforward protocol for the synthesis of a wide range of 4-aryloxysubstituted 2-quinolinones in moderate to excellent yields. Diverse functional groups such as halo, trifluoromethyl, cyano and nitro are well tolerated. Mechanistic studies indicated that 4-hydroxyl-2-quinolinone generated in-situ from o-alkynylanilines and carbon dioxide might be the key intermediate for the reaction.2-Quinolinones represent an important class of nitrogencontaining heterocycles frequently found in a variety of biologically active natural products and pharmaceutically interesting compounds, such as 3-O-methylviridicatin, laquinimod and tipifarnib ( Figure 1). [1] Moreover, 2-quinolinones can serve as useful intermediate in various synthetic transformations. [2] Conventionally, 2-quinolinones have been prepared mainly through two methods: a) the reaction of anilines with bdicarbonyl compounds, such as ethyl acetoacetate, [3] malonic esters, [4] malonic acid, [5] or Meldrum's acid; [6] and b) the condensation of o-aminobenzaldehydes [7] or o-aminobenzophenones [8] with b-dicarbonyl compounds. However, these procedures need strong acids or bases and suffer from disadvantages such as limited substrate scope and low efficiency. Therefore, the development of new and efficient methods for the construction of these important molecules is of great significance.In the past decade, many elegant strategies have been developed for accessing different kinds of 2-quinolinones via transition metal catalysis, including intramolecular cyclization reactions via C-C [9] or CÀN bond [10] formation, Pd-catalyzed formal [3 + 3] cyclizations, [11] Ir- [12a] or Ni-catalyzed [12b] [4 + 2] annulations, and Pd-catalyzed [5 + 1] oxidative cyclocarbonylation. [13] Interestingly, Dong et al. reported a Rh-catalyzed [5 + 2 À 1] transformation between isatins and alkynes for the synthesis of 2-quinolinones. [14] Multi-component reaction strategy has also been applied to the synthesis of these rings, such as Pd-or Rh-catalyzed [3 + 2 + 1] [15] and [4 + 1 + 1] [16] reactions.Notably, carbon dioxide (CO 2 ) has recently emerged as an attractive carbonyl source for the construction of 2-quinolinones due to its nontoxicity, abundance and recyclability. [17] For example, the groups of Yamada [18a] and Zhang [18b] independently reported the synthesis of 4-hydroxyquinolin-2(1H)-ones via a silver-or copper-catalyzed incorporation of CO 2 into oalkynylanilines (Scheme 1, a). Yu and co-workers developed a transition-metal-free lactamization of sp 2 CÀH bonds with CO 2 to generate diverse 2-quinolinones under redox-neutral conditions (Scheme 1, b). [18c] Although great progress has been made in this field, to the best of our knowledge, no straightforward approach has been developed for the synthesis of 4-aryloxy-2-quinolinones...

Synthesis of Trifluoromethylthiolated Quinolinones via Trifluoromethanesulfanamide‐Induced Electrophilic Intramolecular Cyclization of N‐Arylpropynamides

“…On the other aspect, quinolinones is a class of privileged heterocycles and its skeleton is widely presented in many naturally‐occurring compounds or pharmaceuticals that exhibit potential biological activities [5] . For examples, Brexpiprazole, [6] 3‐ O ‐Methylviridicatin, [7] and Tipifarnib [8] (Figure 1) were all pharmaceutical agents bearing quinolinone framework. Since 1970s, searching for novel methods for the synthesis of quinolinones has gained a great deal of attention from organic chemists, and accordingly, many new synthetic routes have been developed.…”

Annulation of 2‐Alkynylanilines: The Versatile Chemical Compounds

“…[7a,62] Qi et al added diaryliodonium salts to the mixture of this reaction to run a three component cyclization furnishing 4-aryloxy-2quinolinones. [63] That's while similar substrates were treated in the presence of Pd(II)-catalytic system and 3,3-diaryl 2,4quinolinediones 56 were formed (Scheme 18). [64] Thus, according to the path of Pd-catalyzed reaction furnishing intermediates 53-55, the type of catalyst will change the fate of product formation.…”

“…Qi et al . added diaryliodonium salts to the mixture of this reaction to run a three component cyclization furnishing 4‐aryloxy‐2‐quinolinones [63] . That's while similar substrates were treated in the presence of Pd(II)‐catalytic system and 3,3‐diaryl 2,4‐quinolinediones 56 were formed (Scheme 18).…”

Copper and In Situ-Generated Triflic Acid Relay-Promoted Four-Component Cascade Reaction for the Construction of Polysubstituted Cycloguanidines

“…Multicomponent reactions have been widely applied to construct various complex molecules using structurally diverse diaryliodoniums under transition-metal-free or -catalyzed reaction conditions over the past decade. For instance, Jiang and Qi developed a base-promoted and Ag-catalyzed three-component reaction of diaryliodonium salts, CO 2 , and amines for the synthesis of O -aryl carbamates and 4-aryloxy-2-quinolinones, respectively. Similar synthesis strategy was applied to biologically relevant S -aryl dithiocarbamates using CS 2 instead of CO 2 under transition-metal- and base-free conditions by Singh and Murarka .…”