Synthesis of Coumarin Derivatives from 4-Oxo-4H-1-benzopyran-3-carboxaldehyde via 3-(Arylaminomethylene)chroman-2,4-dione

Ring transformation of chromone-3-carboxylic acid under nucleophilic conditions

“…The melting point of compound 7a was found to be identical with the earlier reported. 19,20 In a similar manner, compound 7b exists in a stereoisomeric (Z and E) mixture in 2:3 ratio, respectively, (c.f. experimental).…”

Synthesis of 3‐aminomethylidenechroman‐2‐carboxamides by a Sequential One‐pot Three Component Reaction and by Post‐Passerini Condensation Modification

“…3‐Aminomethylidenechroman‐4‐one is a useful precursor for the synthesis of various heterocycles fused at the 3,4‐position of 1‐benzopyran moiety , whereas its tautomer 3‐aminomethylchromen‐4‐one derivatives act as a potent non‐steroidal inhibitors of cytochrome P450 aromatase enzyme . Considering all these utilities of amido and enamino functionalities on the chromone template, synthesis of 3‐aminomethylidene‐4‐oxochroman‐2‐carboxamide is of great interest.…”

Chemistry and application of 4‐oxo‐4H‐1‐benzopyran‐3‐carboxaldehyde

“…Because of the 'chemical symmetry' of the formyl carbon and C-2 of 1, it is very difficult to pinpoint whether a nucleophile is undergoing an initial 1,2-or 1,4-addition to 3-formylchromone. When the reaction between 1 and 15 is mediated by K-10 montmorillonite, chroman-2,4-dione 21 is the exclusive product [16]. The formation of 21 is indicative of an initial 1,4-addition of ArNH 2 to the , -unsaturated aldehyde 1 with concomitant opening of the pyran ring, the resultant intermediate 16 recyclising to 17 (Scheme 1); 17 on elimination of water gives 19 and enamine 20 is the 1,4-adduct of 19 with a second molecule of 15.…”