Reaction of CF 3 -ynones with azides. An efficient regioselective and metal-free route to 4-trifluoroacetyl-1,2,3-triazoles

Regioselective Synthesis of New Family of 2-Substituted 1,2,3-Triazoles and Study of Their Fluorescent Properties

Modification of 5-aryl-4-trifluoroacetyltriazoles at the NH-moiety was investigated. Screening of the alkylation conditions revealed that using Na₂CO₃ as a base and DMF as a solvent of 2-substituted triazoles can be preferentially prepared in up to 86% yield. In the best cases, the amount of minor 1-alkyl isomer was less than 6%. S_NAr reaction of the 5-aryl-4-trifluoroacetyltriazoles with aryl halides having electron-withdrawing groups led to regiospecific formation of 2-aryltriazoles isolated in good-to-high yields. Chan-Lam reaction of the 5-aryl-4-trifluoroacetyltriazoles with boronic acids afforded 2-aryltriazoles as single isomers in up to 89% yield. The subsequent reaction of the prepared 2-aryltriazoles with primary and secondary amines gave a set of amides of 4-(2,5-diaryltriazolyl)carboxylic acid. The fluorescent properties of the prepared 2-substituted derivatives of triazoles were investigated to demonstrate their utility as new efficient luminophores having more than 60% quantum yields.

Acid-Switchable Synthesis of Trifluoromethylated Triazoles and Isoxazoles via Reaction of CF3-Ynones with NaN3: DFT Study of the Reaction Mechanism

A detailed study of the reaction of CF₃-ynones with NaN₃ was performed. It was found that the reaction permits the selective synthesis of either 4-trifluoroacetyltriazoles or 5-CF₃-isoxazoles. The chemoselectivity of the reaction was switchable via acid catalysis. The reaction of CF₃-ynones with NaN₃ in EtOH produced high yields of 4-trifluoroacetyltriazoles. In contrast, the formation of 5-CF₃-isoxazoles was observed under catalysis by acids. This acid-switchable procedure can be performed at sub-gram scale. The possible reaction mechanism was supported by DFT calculations. The synthetic utility of the prepared 4-trifluoroacetyltriazoles was demonstrated.

A green metal-free "one-pot" microwave assisted synthesis of 1,4-dihydrochromene triazoles

The synthesis of several 4-aryl-1,4-dihydrochromene-triazoles was achieved via a metal-free "one-pot" procedure using PEG400 as the sole solvent in an eco-friendly process. Using microwave irradiation, the triazole derivatives were obtained in good yields and short reaction times starting from readily accessible building blocks.

One-Pot Metal-Free Synthesis of 3-CF3-1,3-Oxazinopyridines by Reaction of Pyridines with CF3CO-Acetylenes

The reaction of pyridines with trifluoroacetylated acetylenes was investigated. It was found that the reaction of various pyridines with two molecules of CF₃CO-acetylenes proceeds under mild metal-free conditions. As a result, efficient stereoselective synthesis of 3-arylethynyl-3-trifluoromethyl-1,3-oxazinopyridines was elaborated. Target heterocycles can be prepared in up to quantitative yields.

Theoretical study of the 1,3-DC reaction between fluorinated alkynes and azides: Reactivity indices, transition structures, IGM and ELF analysis

DFT/B3LYP/6-31 + g(d,p) calculations were performed and reactivity indices, transition structures theory were applied to elucidate the molecular mechanism of the reaction between fluorinated alkynes and different azides. The process of cycloaddition operates through a one-step mechanism and an asynchronous transition states. Examination of the energy profile in the gas phase show two possible 1,4 and 1,5 addition channels for amid, the former is preferred. Furthermore, the Parr functions have used to elucidate the reaction's regioselectivity. It was noted that the addition of solvent (DMSO) does not affect the regioselectivity of the reactions. Analysis of charge transfer in the transition structures shows a moderate polar character for the majority of the studied reactions. Moreover, the independent gradient model based on promolecular density (IGM) has been used to evaluate the asynchronicity of the formation of the two new sigma bonds. Finally, the ELF calculation has been performed to clearly describe the formation of the previous bonds along the IRC path.

Electrophilic halogenation of hydrazones of CF3-ynones. Regioselective synthesis of 4-halo-substituted 3-CF3-pyrazoles

An efficient approach for the synthesis of 4-halo-3-CF3-pyrazoles was elaborated using the cyclization of hydrazones of CF3-ynones induced by electrophilic halogenation. This method can be used for the regioselective synthesis of 3-CF3-pyrazoles substituted at the 4-position with any halogen (I, Br or Cl). The high (up to quantitative) yields, mild conditions and simplicity of the reaction protocol are the advantages of the proposed method. It was demonstrated that cross-coupling with 4-iodo-3-CF3-pyrazoles can be used for the synthesis of a broad family of tetrasubstituted pyrazoles. Moreover, it was found that this method is suitable for the synthesis of 4-substituted derivatives of Celebrex and SC-560.