Block copolymers in the synthesis of gold nanoparticles. Two new approaches: Copolymer aggregates as reductants and stabilizers and simultaneous formation of copolymer aggregates and gold nanoparticles

In this article, innovative applications of amphiphilic triblock and pentablock copolymers in the synthesis of gold nanoparticles are reported. The synthesis of gold nanoparticles is performed using two methods. In the first method, micellar aggregates of block copolymers and AuCl₄^? ions directly react in water; the nanoparticles obtained by this method are variable in size and are associated with copolymer aggregates. In the second method, two processes take place simultaneously: the aggregation of block copolymers and the reduction of Au (III) by the copolymers to form nanoparticles. In contrast with the first method, in this case, the nanoparticles obtained are located inside the copolymer aggregates. In both methods of synthesis, the block copolymers act simultaneously as reducing and stabilizing agents. To understand the role of copolymer aggregates in the synthesis of nanoparticles, molecular simulation methods are used. The gold nanoparticles, copolymer aggregates, and nanocomposite systems are characterized using transmission electron microscopy and dynamic light scattering. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3069–3079     

DAST promotes the synthesis of new 5-(trifluoromethyl)-3-(1,1-difluoroethan-2-yl)-1H-pyrazoles

This study describes, firstly, the synthesis of a new precursor, 4,6,6-trimethoxy-1,1,1-trifluorohex-3-en-2-one (1), from the trifluoroacetylation reaction of 1,1,3,3-tetramethoxybutane, in 65% yields. Afterwards, the reaction of 1 with two hydrazines (NH₂NHR, where R = 2-furanoyl, C₆F₅) led to a new series of 4,5-dihydro-1H-pyrazoles, containing an acetal-protected aldehyde function as substituent, in 90-97% yields. In a subsequent step, the dehydration reactions of these 4,5-dihydro-1H-pyrazoles gave the respective aromatic 1H-pyrazoles. Finally, we report the results of the deprotection reactions of the acetals to obtain the respective aldehyde function, as well as, the subsequent fluorination reaction using DAST, leading to new difluorinated derivatives in 55-60% yields.     

Haloacetylated enol ethers: 15. Study of the regiochemistry of the cyclo‐condensation of β‐alkoxyvinyl trihalomethyl ketones with N‐methyl thiourea

A study of the regiochemistry of the cyclo‐condensation reaction of ß‐alkoxyvinyl trihalomethyl ketones with an unsymmetric dinucleophile N‐methyl thiourea to afford a series of 1‐methyl‐3‐(4,4,4‐trifluoro[chloro]‐3‐oxo‐1‐butenyl)thioureas and the corresponding N‐methyl pyrimidinethione derivatives is reported. The absolute assignment of the position of the N‐methyl group in the pyrimidine ring was obtained through a nmr study based on two dimensional HMBC and NOESY experiments.     

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.     

Synthesis of 1‐Arylethyl‐2‐arylethylamino‐5‐trifluoroacetyl‐1,2,3,4‐tetrahydropyridines and Related Compounds with Potential Cell Efflux Pump Inhibition

This study reports a simple, fast, and efficient method for the synthesis of a new series of 1‐arylethyl‐2‐arylethylamino‐5‐trifluoroacetyl‐1,2,3,4‐tetrahydropyridines and related compounds from the reaction of 2‐alkoxy‐5‐trifluoroacetyl‐3,4‐dihydro‐2H‐pyrans with 2‐arylethanamines and related 2‐ethanamines. The desired tetrahydropyridines were obtained in excellent yields (90–98%), through a reaction that can be described as an AAB′ three‐component reaction protocol following an ANRORC‐type mechanism.     

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.     

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.