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...
