Reactivity of 3-formyl- and 3-cyanothiochromones toward some N- and C-nucleophiles. Novel synthesis of 3-substituted 2-aminothiochromones

The reactions of 3-formylthiochromone with o-phenylenediamines, o-aminobenzenethiol, and indoles proceeded at the aldehyde group to give 3-(benzimidazol-2-yl)thiochromone, 3-(benzothiazol-2-yl)thiochromone, and 3-di(indol-3-yl)methylthiochromones, respectively. 3-Formyl- and 3-cyanothiochromones react with primary aromatic amines and phenylhydrazine to give the corresponding anils and phenylhydrazones of 3-formyl- and 2-amino-3-formylthiochromones. The reaction of 3-cyanochromones with o-phenylenediamines gave 2-amino-3-[(2-aminophenyl)iminomethyl]-4H-chromen-4-ones.     

A general strategy for the synthesis of difluoromethyl-containing pyrazoles, pyridines and pyrimidines

Difluoromethyl-containing heteroannulated pyridines, pyrimidines and pyrazoles are prepared by a two step method. The regioselective cyclizations of electron-excessive aminoheterocycles, hydrazines and amidines with CF₂Cl-substituted 1,3-dicarbonyl compounds provide the corresponding CF₂Cl-substituted heterocycles. Subsequent radical reactions with trimethylstannane or allyltrimethylstannane gave difluoromethyl-containing heteroannulated pyridines, pyrimidines and pyrazoles, respectively.     

Synthesis of functionalized arylpyridines and -pyrimidines by domino [4+2]/retro [4+2] cycloadditions of electron-rich dienes with alkynylpyridines and -pyrimidines

Aryl-substituted pyridines and pyrimidines were prepared by [4+2] cycloadditions of alkynyl-substituted pyridines and -pyrimidines with electron-rich dienes. The reactions proceed by formation of a bridged cycloadduct and subsequent thermal extrusion of ethylene. The pyridine moiety plays a crucial role for the success of the reaction.     

3-Methoxalylchromones--versatile reagents for the regioselective synthesis of functionalized 2,4'-dihydroxybenzophenones, potential UV-filters

The reaction of 1,3-bis-silyl enol ethers with 3-methoxalylchromones affords a great variety of functionalised 2,4'-dihydroxybenzophenones. These products are formed by a domino Michael/retro-Michael/Mukaiyama-aldol reaction. The synthesized compounds are promising candidates for the synthesis of the novel UV-A/B and UV-B filters.     

Synthesis of heteroannulated 3-nitro- and 3-aminopyridines by cyclocondensation of electron-rich aminoheterocycles with 3-nitrochromone

3-Nitrochromone reacts with electron-rich aminoheterocycles (in glacial acetic acid at reflux) and anilines (in a mixture of DMF and TMSCl at 100–140 °C) to give a variety of hetero(carbo)annulated 3-nitropyridines. The reaction, involving a formal [3+3] cyclocondensation, proceeds in high yields and appears not to be influences greatly by the nature of the 1,3-C,N-dinucleophile as seen from the thorough scope study. The synthetic utility of the products was demonstrated by their conversion into the corresponding 3-aminopyridine derivatives. An NMR study and X-ray crystallographic analysis are reported.     

Cu-Catalyzed Arylation of Bromo-Difluoro-Acetamides by Aryl Boronic Acids,Aryl Trialkoxysilanes and Dimethyl-Aryl-Sulfonium Salts: New Entries to Aromatic Amides

We describe a mechanism-guided discovery of a synthetic methodology that enables the preparation of aromatic amides from 2-bromo-2,2-difluoroacetamides utilizing a copper-catalyzed direct arylation. Readily available and structurally simple aryl precursors such as aryl boronic acids, aryl trialkoxysilanes and dimethyl-aryl-sulfonium salts were used as the source for the aryl substituents. The scope of the reactions was tested, and the reactions were insensitive to the electronic nature of the aryl groups, as both electron-rich and electron-deficient aryls were successfully introduced. A wide range of 2-bromo-2,2-difluoroacetamides as either aliphatic or aromatic secondary or tertiary amides were also reactive under the developed conditions. The described synthetic protocols displayed excellent efficiency and were successfully utilized for the expeditious preparation of diverse aromatic amides in good-to-excellent yields. The reactions were scaled up to gram quantities.     

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

While 2-(trifluoromethyl)chromones react with cyanoacetamides in the presence of sodium ethoxide to produce 6-(2-hydroxyaryl)-4-(trifluoromethyl)-2-oxo-1,2-dihydropyridine-3-carbonitriles, their reactions with ethyl cyanoacetate and diethyl malonate under the same conditions took an entirely different course and gave novel functionalized derivatives of 6H-benzo[c]chromen-6-one.     

4-Chloro-3-(trifluoroacetyl)- and 4-chloro-3-(methoxalyl)coumarins as novel and efficient building blocks for the regioselective synthesis of 3,4-fused coumarins

4-Chloro-3-(trifluoroacetyl)- and 4-chloro-3-(methoxalyl)coumarins react with electron-rich aminoheterocycles, dimethyl 1,3-acetonedicarboxylate, hydrazines, alkyl thioglycolates, and methyl sarcosinate to give a variety of 3,4-heteroannulated coumarins. The starting materials were prepared by the reaction of 4-hydroxycoumarin with trifluoroacetic anhydride and methyl 2-chloro-2-oxoacetate in the presence of trimethylsilylchloride. An NMR study and X-ray crystallographic analysis are reported.