Reactions of 2-(trifluoromethyl)chromones with cyanoacetamides, ethyl cyanoacetate and diethyl malonate. Unexpected synthesis of benzo[c]coumarin derivatives

Reactions of 2‐Methylchromones with Cyanoacetamides and Ethyl Cyanoacetate. Synthesis of 6‐(2‐Hydroxyaryl)‐4‐methyl‐2‐oxo‐1,2‐dihydropyridine‐3‐carbonitriles and 7‐Hydroxy‐6‐imino‐9‐methyl‐6H‐benzo[c]chromene‐8‐carbonitriles

“…as the α‐pyrone 4 (R═H). However, in contrast with this structure, its composition corresponded to a 1:2 adduct, C 15 H 10 N 2 O 2 , which was assigned the structure 7‐hydroxy‐6‐imino‐9‐methyl‐6 H ‐benzo[ c ]chromene‐8‐carbonitrile ( 6a ) on the basis of elemental analysis, 1 H NMR, 13 C NMR, IR spectroscopies, and comparison of the spectroscopic data with the data reported for related systems . In particular, the aromatic protons of compound 6a at δ 7.37 (H‐4), 7.40 (H‐2), 7.61 (H‐3), and 8.26 (H‐1) compare well with those of trifluoromethylated analog, 7‐hydroxy‐6‐imino‐9‐(trifluoromethyl)‐6 H ‐benzo[ c ]chromene‐8‐carbonitrile ( 5 , R═H, δ 7.41, 7.43, 7.67, and 8.38, respectively).…”

“…As mentioned earlier, the previous workers reported that the reaction of 1a , 1b with ethyl cyanoacetate leads to compounds 4 (R═H, Me), and their claim has been favorably reviewed . However, the 2‐pyrone ring formation was not firmly established, and in light of the known behavior 2‐(trifluoromethyl)chromones in reaction with ethyl cyanoacetate, which afforded 7‐hydroxy‐6‐imino‐9‐(trifluoromethyl)‐6 H ‐benzo[ c ]chromene‐8‐carbonitriles 5 (Scheme ) , it was anticipated that the process would follow a 1:2 instead of a 1:1 stoichiometry and proceed by double nucleophilic attack of the base‐activated ethyl cyanoacetate to the chromone system. We therefore decided to repeat the condensation of chromones 1a , 1b , 1c , 1d with ethyl cyanoacetate as originally reported .…”

Synthetic protocols on 6$H$-benzo[$c$]chromen-6-ones: a review

“…The reaction was proposed to be initiated by the nucleophilic acetonedicarboxylate ( 31) nucleophilic attack at C-2 chromone carbon, followed by chromone ring opening, which forms intermediate 33. On the basis of the above precedent reports, 22,23 Iaroshenko and coworkers reported the synthesis of 6Hbenzo[c ]chromen-6-ones utilizing the base mediated cyclocondensation of 1,3 and 1,5-dicarbonyl compounds with 4-chloro-3-formylcoumarin (46). 24 The 1,5-dicarbonyls with two acidic methylene groups follow 1:1 stoichiometry, because the two groups are involved in cyclocondensation with the coumarin aldehyde group and C-4 carbon (Scheme 5).…”

Ring Opening and Recyclization Reactions of 3‐Nitrochromone with Some Nucleophilic Reagents

“…Introduction of an electron‐withdrawing group into the 3‐position of chromone changes the reactivity of the γ‐pyrone ring towards nucleophilic reagents and opens up a broad synthetic scope of this important oxygen‐containing heterocyclic systems . 3‐Substituted chromones are very active substrates for nucleophilic attack at C‐2 position and used as valuable synthetic intermediates in the preparation of a variety of heterocyclic compounds . 3‐Nitrochromone has received attention as building blocks for construction of a diversity of heterocycles especially heterannulated 3‐nitropyridines via its reactions with some electron‐rich heterocyclic enamines .…”