Solvent effects on the O NMR chemical shifts of 4-dimethylsulfoximide-1,1,1-trifluoro-3-alken-2-ones

A multi-linear-regression analysis using the Kamlet-Abbout-Taft (KAT) solvatochromic parameters in order to elucidate and quantify the solvent effects on the chemical shifts of three 4-dimethylsulfoximide-1,1,1-trifluoro-3-buten-2-ones is reported. The predominant conformational structures of compounds has been determined by energy minimization calculations using the Austin Model (AM1) semi-empirical method, which has been used to explain the NMR chemical shifts for CO and SO groups. The chemical shifts of carbonyl and sulfoximide oxygen’s of molecules showed similar dependencies (in ppm) on the solvent polarity-polarizability and the solvent hydrogen-bond-donor (HBD) acidities. The influence of solvent hydrogen-bond-acceptor (HBA) basicities was little significant.     

A microwave improvement in the synthesis of the quinazoline scaffold

A rapid and efficient microwave-assisted protocol is described that greatly improves a recent synthetic method developed for quinazoline synthesis. The synthetic protocol is based on the use of cycles of microwave irradiation. The optimization process is reported and the experimental results are compared with those of the conventional synthetic route.     

A new access to quinazolines from simple anilines

A new synthetic pathway to quinazolines is described. This new method uses hexamethylenetetramine in TFA and potassium ferricyanide in aqueous ethanolic KOH, starting from simple N-protected anilines. The method affords substituted quinazolines with high selectivities and good yields, reducing reaction-time and work-up operations.     

Microwave assisted regiospecific synthesis of 5‐trifluoromethyl‐4,5‐dihydropyrazoles and—pyrazoles

The regiospecific synthesis of a series of twelve 5‐trifluoromethyl‐4,5‐dihydropyrazoles and ‐pyrazoles from the cyclocondesation reaction of 4‐alkoxy‐1,1,1‐trifluoro‐3‐alken‐2‐ones [F₃CC(O)CH=C(R¹)OR, where R¹ = Me, Et, Pr, iso‐Pr, Bu, iso‐Bu, Ph, H; and R = Me, Et] with phenylhydrazine in toluene by environmentally benign microwave induced techniques is reported. It is shown that under appropriated conditions, the variation of microwave irradiation power leads to 4,5‐dihydropyrazole or pyrazole derivatives. This paper also includes the use of montmorillonite K‐10 as a solid support for the synthesis of pyrazoles under solvent free conditions.     

Preparation of new 2‐amino‐ and 2,3‐diamino‐pyridine trifluoroacetyl enamine derivatives and their application to the synthesis of trifluoromethyl‐containing 3H‐pyrido[2,3‐b][1,4] diazepinols

The synthesis of a novel series of the intermediates N²(N³)‐[1‐alkyl(aryl/heteroaryl)‐3‐oxo‐4,4,4‐trifluoroalk‐1‐en‐1‐yl]‐2‐aminopyridines [F₃CC(O)CH?CR¹(2? NH?C₅H₃N)] and 2,3‐diaminopyridines [F₃CC(O)CH?CR¹(2‐NH₂‐3‐NH? C₅H₃N)], where R¹ = H, Me, C₆H₅, 4‐FC₆H₄, 4‐CIC₆H₄, 4‐BrC₆H₄, 4‐CH₃C₆H₄, 4‐OCH₃C₆H₄, 4,4′‐biphenyl, 1‐naphthyl, 2‐thienyl, 2‐furyl, is reported. The corresponding series of 2‐aryl(heteroaryl)‐4‐trifluoromethyl‐3H‐pyrido[2,3‐b][1,4]diazepin‐4‐ols obtained from intramolecular cyclization reaction of the respective trifluoroacetyl enamines or from the direct cyclocondensation reaction of 4‐methoxy‐1,1,1‐trifluoroalk‐3‐en‐2‐ones with 2,3‐diaminopyridine, under mild conditions, is also reported.     

Microwave-assisted synthesis and antimicrobial activity of 5-trihalomethyl-3-arylisoxazoles

A series of twelve 5-trihalomethyl-3-arylisoxazoles was synthesized and screened for antibacterial and antifungal activities. The compounds were synthesized from the cyclondensation of 1,1,1-trihalo-4-alkoxy-3-alken-2-ones [CX ₃C(O)C(R ²)=C(R ¹)OR, where X = Cl and F; R=Me; R ²=H; R ¹=H, Me, F, Cl, Br, and NO₂] with hydroxylamine hydrochloride through a rapid one-pot reaction via microwave irradiation. Some of the 5-trihalomethyl-3-arylisoxazoles exhibited good in vitro anti-Cryptococcus activity. Correspondence: Marcos A. P. Martins, Núcleo de Química de Heterociclos (NUQUIMHE), Centro de Ciências Naturais e Exatas, Departamento de Química, Universidade Federal de Santa Maria, 97.105-900 Santa Maria, RS, Brazil.     

Haloacetylated enol ethers. 11. Synthesis of 1-methyl- and 1-phenyl pyrazole-3(5)-ethyl esters. A one-pot procedure

A one-pot synthesis of 1-methyl- and 1-phenylpyrazole-3(5)-ethyl esters 2,3a-e by the cyclocondensation of β-alkoxyvinyl trichloromethyl ketones 1a-e with methyl and phenyl hydrazine hydrochloride under mild conditions, is reported. A study using compounds 1a-e with different substituents proved that these are versatile building blocks for the synthesis of pyrazole derivatives, having a 3(5)-ethoxycarbonyl substituent in good yields (60–89%). The hydrazine and β-alkoxyvinyl trichloromethyl ketone substituent effects on the reaction regiochemistry on the formation of the 1,3- and 1,5-isomer were observed.     

General method for dehydration, intramolecular cyclization, and fluorination of trifluoromethyl-1H-pyrazoles using DAST

In this study, the versatile diethylaminosulfur trifluoride (DAST), a well-known fluorinating agent, was applied in the dehydration, intramolecular cyclization, and mono- and difluorination reactions of some 5-trifluoromethyl-1H-pyrazoles and 2-pyrazolines employing a general, mild, and efficient methodology. The azole precursors were synthesized from the reactions of acyclic and cyclic trifluoroacetylated enol ethers with hydrazines [NH₂NHR, where R = C₆H₅, C₆F₅, 2-Furanoyl] and showed a differentiated chemical behavior in the presence of DAST.