Reactions of β-methoxyvinyl trifluoromethyl ketones with 2-pyridinecarboxamidrazone: A convenient route to trifluoromethylated 4,5-dihydro-1H-1-picolinoylpyrazole hydrochlorides

A new series of six 3-aryl-5-hydroxy-5-trifluoromethyl-4,5-dihydro-1H-1-picolinoylpyrazole hydrochlorides were synthesised in one-step in high yields by the reaction of β-methoxyvinyl trifluoromethyl ketones with 2-pyridinecarboxamidrazone in the presence of hydrochloric acid. The hydrochloride salts were easily converted to the respective new series of free trifluoromethylated 4,5-dihydro-1H-1-picolinoylpyrazoles using triethylamine in anhydrous diethyl ether. X-ray structure and NMR data from the pyrazole hydrochlorides are reported.     

Convergent procedure for the synthesis of trifluoromethyl-containing N-(pyridinyl-triazolyl)pyrimidin-2-amines

This study describes a simple and efficient procedure to synthesize a novel series of fourteen 4-substituted N-(5-pyridinyl-1H-1,2,4-triazol-3-yl)-6-(trifluoromethyl)pyrimidin-2-amines, where the 4-substituents are H, CH₃, C₆H₅, 4-FC₆H₄, 4-CH₃C₆H₄, 4-CH₃OC₆H₄ and 2-Furyl; from the cyclocondensation reaction of N-[5-(pyridinyl)-1H-1,2,4-triazol-3-yl]guanidines with 4-alkoxy-4-alkyl(aryl/heteroaryl)-1,1,1-trifluoroalk-3-en-2-ones. The reactions were carried out in ethanol under reflux for 18 h and led to 40-68% yields. N-(Pyridyl-triazolyl)guanidine precursors were further obtained from reactions of cyanoguanidine with nicotinic or isonicotinic acid hydrazides and the halogenated enones from trifluoroacetylation of enolethers or acetals.     

Organoallylaluminum reagents promote easy access to trihalomethyl triazolyl homoallylic alcohols analogous to rufinamide

The results of allylation reactions employing allylaluminum reagents are described for 5-substituted (2,6-difluorobenzyl)-4-trifluoro(chloro)acetyl-1H-1,2,3-triazoles (1), in which the 5-substituents are H, Me, and Ph. The allylating reagents were generated in situ by the catalytic insertion of aluminum into allyl and crotyl bromides (2), in order to furnish a new series of twelve trihalomethyl triazolyl homoallylic alcohols (3) at yields of up to 94%. The excellent reactivity of these organoallyl reagents is highlighted as an economical alternative to the indium-mediated reactions to produce homoallylic alcohols, which are important building blocks in organic synthesis.     

13C NMR Chemical Shift of β-Alkoxyvinylketones: II. Empirical Substituent Effects in β-Aryl-β-Methoxyvinyltrihalomethylketones

Evaluation by empirically derived equations for the substituent effect (α,β,γ,δ) on the ¹³C NMR chemical shifts for C-1, C-2, C-3 and C-4 in β-aryl-β-methoxyvinylhalomethylketones 1a-g to 2a-g [R³C(O)-CH=C(Ar)-OMe, where R³ = CCl₃, CF₃ and Ar = p-YC₆H₄ (Y = H, Me, MeO, F, Cl, Br, NO₂)], taking as reference the β-ethoxyvinyltrichloromethylketone (3), is reported. From the calculated values for the α,β,γ,δ effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds 1,2. The ¹³C chemical shifts of the C-1, C-2, C-3, C-4 of these compounds, can be estimated with good to rasoable precision: 84% of the calculated chemical shifts are found to be within ±1.0ppm, and 100% are found to be within ±1.5ppm. The Y-Effects on C-3 and C-4 are compared with carbon charge densities (qr).     

Electron paramagnetic resonance and the thermoluminescence emission mechanism of the 280 °C peak in natural andalusite crystal

Samples of natural andalusite (Al₂SiO₅) crystal have been investigated in terms of thermoluminescence (TL) and electron paramagnetic resonance (EPR) measurements. The TL glow curves of samples previously annealed at 600 °C for 30 min and subsequently gamma-irradiated gave rise to four glow peaks at 150, 210, 280 and 350 °C. The EPR spectra of natural samples heat-treated at 600 °C for 30 min show signals at g=5.94 and 2.014 that do not change after gamma irradiation and thermal treatments. However, it was observed that the appearance of a paramagnetic center at g=1.882 for the samples annealed at 600 °C for 30 min followed gamma irradiation. This line was attributed to Ti³⁺ centers. The EPR signals observed at g=5.94 and 2.014 are due to Fe³⁺. Correlations between EPR and TL results of these crystals show that the EPR line at g=1.882 and the TL peak at 280 °C can be attributed to the same defect center.     

Ultrasound promoted synthesis of 5-hydroxy-5-trihalomethyl-4,5-dihydroisoxazoles and beta-enamino trihalomethyl ketones in water

A convenient method for the preparation of 5-hydroxy-5-trihalo-4,5-dihydroisoxazoles and beta-enamino trihalomethyl ketones, from the reaction of 1,1,1-trihalo-4-alkoxy-3-alken-2-ones with hydroxylamine and anilines, respectively, using water as solvent and under ultrasound irradiation is reported.     

Efficient synthesis of 6-aryl-4-trifluoromethyl/ethoxycarbonyl-2H-pyran-2-ones through self-condensation of penta-2,4-dienenitriles

An efficient synthesis of two new series of 6-aryl-4-trifluoromethyl-2H-pyran-2-ones and 6-aryl-4-carboxyethyl-2H-pyran-2-ones, obtained through the self-condensation reaction of 5-aryl-5-methoxy-3-(trifluoromethyl)penta-2,4-dienenitriles 3 and ethyl 4-aryl-2-(cyanomethylene)-4-methoxybut-3-enoates 4 respectively, is reported. The self-condensation reaction of the enoates 4 was performed in water in the presence of hydrochloric acid whereas the self-condensation reaction of the penta-2,4-dienenitriles 3 required the use of zinc bromide and hydrochloric acid in order to give the respective 2H-pyran-2-ones. Products were obtained up to 97% yield.     

Chemoselective fluorination of 2-hydroxy-3,4,7,8-tetrahydro-2H-chromen-5(6H)-ones using DAST

In this study, diethylaminosulfur trifluoride (DAST) was successfully applied in monofluorination reactions of some trifluoromethyl substituted 2-hydroxy-2H-chromenones, employing a general, mild, and efficient methodology. The fluorinated compounds (2-fluoro-2H-chromenones) were synthesized as unique products by a chemoselective reaction in 63-81% yield despite the presence of different reactive sites subjected to reactions with DAST.