Novel Method of Tetramic Acid Synthesis: Silver-Catalyzed Carbon Dioxide Incorporation into Propargylic Amine and Intramolecular Rearrangement

Tetramic acid derivatives have been studied as biologically active heterocycle structures for pharmaceutical or agricultural chemicals. Conventional preparative approaches often require highly functionalized starting materials and harsh heating conditions in basic media. The present report provides a conceptually new synthetic strategy for the synthesis of tetramic acid derivatives from easily available propargylic amines and carbon dioxide with a silver salt and DBU under mild reaction conditions

SilverCatalyzed Cascade Carboxylation and Cyclization of Trimethyl(2-methylenebut-3-yn-1-yl)silane Derivatives

C–C bond-forming carboxylation and cyclization of trimethyl­(2-methylenebut-3-yn-1-yl)­silane derivatives and carbon dioxide was developed. Silver catalysts and CsF promoted the reaction to afford the corresponding 2-furanone and 2-pyrone derivatives in good-to-high yields. The structure of the 2-furanone was confirmed by single-crystal X-ray crystallography, which revealed that the geometry of the <i>exo</i>-olefin was that of a <i>Z</i>-isomer. When an aromatic ring-substituted alkyne was used, 2-furanone derivatives were selectively obtained via 5-<i>exo-dig</i> cyclization, whereas the reaction of alkyl-substituted alkynes produced 2-pyrone derivatives with high selectivity

Efficient Preparation of 4‑Hydroxyquinolin-2(1<i>H</i>)‑one Derivatives with Silver-Catalyzed Carbon Dioxide Incorporation and Intramolecular Rearrangement

Although 4-hydroxyquinolin-2(1<i>H</i>)-one derivatives have attracted much attention due to their biological benefits, conventional reactions under harsh heat conditions must be employed to provide these key compounds. In the presence of a catalytic amount of silver salt, various <i>o-</i>alkynylanilines were treated with carbon dioxide and a base under mild reaction conditions to afford the corresponding 4-hydroxyquinolin-2(1<i>H</i>)-one derivatives in high yield

Decarboxylative Intramolecular [3 + 2] Cycloaddition of Cyclic Enol Carbonates: Construction of a Bicyclo[3.3.0]octanone Skeleton

Stereoselective synthesis of bicyclic cyclopentanones was achieved by sequential Tf2O-catalyzed decarboxylation and intramolecular [3 + 2] cycloaddition reactions of cyclic enol carbonates bearing an alkene unit. Four stereogenic centers in the obtained cyclopentanone were stereoselectively constructed. This method could be applied to the synthesis of various fused bicyclic products in moderate-to-good yields

Access to Tetronic Acids via Silver-Catalyzed CO₂ Incorporation into Conjugated Ynones

Facile and versatile access to highly functionalized tetronic acids has been successfully achieved through the reaction of conjugated ynones with carbon dioxide. In the presence of a base, the enolates generated from the ynones capture CO₂ via a carbon–carbon bond-forming reaction, accompanied by a 5-<i>exo-dig</i> cyclization reaction of the resulting carboxylate to the alkyne, activated by a silver catalyst. The present method should be applicable to the synthesis of a wide variety of tetronic acids

Silver-Catalyzed Incorporation of Carbon Dioxide into <i>o-</i>Alkynylaniline Derivatives

Benzoxazine-2-one derivatives are important heterocycle structures because of their various pharmaceutical activities, though their synthetic methods had been limited. In some cases, toxic reagents, such as phosgene or carbon monoxide, are required. It was found that a silver catalyst successfully promoted the incorporation of CO₂ into <i>o-</i>alkynylanilines to afford the corresponding benzoxazine-2-ones bearing <i>Z exo</i>-olefin via 6-<i>exo-dig</i> cyclization at the activated C–C triple bond

Homogeneous Enantioselective Catalysis in a Continuous-Flow Microreactor: Highly Enantioselective Borohydride Reduction of Ketones Catalyzed by Optically Active Cobalt Complexes

Highly enantioselective homogeneous catalysis under continuous-flow conditions was established for the cobalt-catalyzed borohydride reduction of tetralone derivatives. A microreactor allowed higher reaction temperature with the residence time of 12 min than the corresponding batch system to maintain enantioselectivity as well as reactivity. The present system was directly applied to gram-scale synthesis to afford the reduced product with 92% ee