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Ultrasound irradiation, an efficient and innocuous technique of reagent activation for synthesizing organic compounds, has been applied with success to transform seven carboxylic acids to fourteen secondary amides in good to excellent yields. The reaction has worked well either with aryl or alkyl carboxylic acids as well as with aromatic or aliphatic amines. This methodology is expeditious and reliable for preparing secondary carboxamides which in many cases are embedded in the C-5 side-chain of 1,2,4-oxadiazoles (14, 15, 17-27). The elemental analyses of new compounds (19-27) in conjunction with the spectral data of all synthesized amides gave an idea about their structures, while the crystallographic data of one of the compounds (26) supplied information concerning the configurational behavior of the amidic part and also the conformational aspect of the entire molecule in the crystalline state.

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SummaryA library of ten 1,3-diyne-linked peptoids has been synthesized through an Ugi four-component reaction (U-4CR) followed by a copper-catalysed alkyne homocoupling (Glaser reaction). The short and chemoselective reaction sequence allows generating diverse (pseudo) dimeric peptoids. A combinatorial version allows the one-pot preparation of, e.g., six-compound-libraries of homo- and heterodimers verified by ESI-MS and HPLC. In a preliminary evaluation, some compounds display moderate activity against the Gram-positive bacterium Bacillus subtilis.

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The synthesis of 3-(3-aryl-1,2,4-oxadiazol-5-yl)propionic acids from arylamidoximes and succinic anhydride under focused microwave irradiation conditions is described. The new synthetic method furnished the desired products in 2-3 min and good yields. Furthermore, the previously complicated purification procedure has been simplified in a manner which is quick, eco-friendly and cost-effective. Larvicidal bioassay and fungal growth inhibitory tests were performed using several 3-(3-aryl-1,2,4-oxadiazol-5-yl)propionic acids. These acids presented strong larvicidal activity against L4 larvae of Aedes aegypti. The results suggest that larvicidal activity might be correlated with the presence of electron-withdrawing substituents in the para position of the phenyl ring except the fluorine atom. The alterations observed in the larvae spiracular valves of the siphon and anal papillae by 1,2,4-oxadiazoles in the larvicidal bioassay are responsible for larvae's death. Furthermore, all acids inhibited the fungal growth of five different types of fungi, viz., Fusarium solani, F. oxysporum, F. moniliforme, F. decemcellulare and F. lateritium in a preliminary evaluation. Both of these activities are being disclosed for the first time for 1,2,4-oxadiazole-5-yl ring linked at C-3 of propionic acid.

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A series of highly p-conjugated nonsymmetrical liquid crystals, based on the core 3,5-(disubstituted)-1,2,4-oxadiazole with a shape similar to a hockey stick, were successfully synthesized by convergent Sonogashira coupling reaction between the building blocks of aryl iodides and the corresponding terminal arylacetylenes, using 3-[4-(decyloxy)phenyl]-5-(haloaryl)-1,2,4-oxadiazoles or decyl 4-iodobenzoate (10) and terminal arylacetylenes. This versatile synthetic route yielded luminescent mesogens with smectic and nematic phases, typical of calamitic compounds.In an attempt to optimize molecular properties for display and optical applications, considerable attention has been given to the design and synthesis of liquid crystalline compounds with suitable selection of the core fragment, linking group, and terminal functionality. 1 Highly p-conjugated liquid crystal molecules containing heterocycles have attracted increasing interest in the field of organic light emitting diodes (OLEDs), where electron-deficient heteroaromatic rings can lead to a good charge-transporting materials allied with its inherent self-organization ability, and strong fluorescence. 2 1,3,4-Oxadiazole-based liquid crystals with high thermal stability and very efficient blue luminescence have been synthesized. 3 In addition, the carbon-carbon triple bond is a good spacer group in liquid crystals, which produces a highly p-polarizable and conjugated moiety. Liquid crystals containing a carbon-carbon triple bond are very interesting materials due to their large birefringence, 4 large index of refraction parallel to the director, large electric polarizability and the ability to form optical films transparent in the visible. The Sonogashira coupling 5 between aryl halides and terminal acetylenes, the most common employed synthetic technique to build carbon-carbon triple bonds, has been widely used in the synthesis of functional materials. 6Herein, we report an efficient synthesis of a series of liquid crystalline compounds 1a-f, which possess a 1,2,4-oxadiazole heterocyclic nonsymmetrical core and similar hockey stick shape (Figure 1). 7 In our attempts to gain a better understanding of the chemical structure versus thermal/optical property relationships, different aromatic moieties were linked to the central core by a carbon-carbon triple bond. These aromatic groups [phenyl, 2-naphthyl, 4-(piperazin-1-yl)phenyl, or 4-(alkoxycarbonyl)phenyl], were chosen by considering an elongation of the liquid crystal molecule rod, thus increasing the length-to-breadth ratio, and also an extension in the pconjugated system, with strong electron-donating (e.g., OR, NR 2 ) and electron-withdrawing (e.g., NO 2 , C=O) substituents.The initial synthesis of the intermediates containing the 1,2,4-oxadiazole ring (compounds 6a,b) was carried out as shown in Scheme 1. First, N-hydroxyimidamide 3 was prepared from 4-(decyloxy)benzonitrile (2) 8 by the Tiemann reaction 9 using hydroxylamine hydrochloride, and potassium hydroxide in a methanol-water mixture.The formation of...