Letters in Organic Chemistry - Volume 10, Issue 1, 2013

Under Mitsunobu conditions N-Boc-2-(hydroxymethyl)piperidine acts as a source of tert-butyl residue for the conversion of phenols into aryl tert-butyl ethers under neutral conditions. This reactivity can be attributed to a neighboring group contribution which strongly depends on the structure of the employed N-Boc-aminoalcohol. Five other, closely related N-Boc-aminoalcohols investigated here did not show this special reactivity, and gave the regular Mitsunobu coupling products.

In many chemical processes, Lewis acids and bases are used to activate reactants simultaneously or sequentially. The integration of both Lewis base and Lewis acid has great potential to enhance known reactivity and drive the development of new chemical reactions with high value. In this topic, we disclose herein, the synthesis of 3,4- Dihydropyrimidin-2(1H)-ones, via one-pot three-component Biginelli condensation, in the presence of Lewis acid/ tertiary amine as a novel cooperative catalytic system. The high activity and the synergistic effect of this system are well pronounced.

Tungstate sulfuric acid (TSA) as a solid acid catalyst has been synthesized and used in Paal–Knorr synthesis of some novel and known pyrroles under solvent-free conditions. Catalyst loadings can be as low as 1 mol % to give high yields of the corresponding pyrroles at 60 °C. To make the catalyst, sodium tungstic reacted with chlorosulfonic acid in nhexane.

In this paper, a superparamagnetic graphene-Fe3O4 nanocomposite (G-Fe3O4) was synthesized by a coprecipitation method, which was used as an efficient catalyst for the reduction of nitroarenes with hydrazine hydrate for the first time. The method has been applied on a broad range of compounds with different properties. The G-Fe3O4 catalyst can be readily recovered and reused without a significant loss of catalytic activity.

A triazine-based multi-branched platinum(II) acetylide complex was synthesized and fully characterized. The photophysical properties, electrochemical properties and first order hyperpolarizability were studied.

A rapid and efficient method for the synthesis of 1,3,5-triarylpent-2-ene-1,5-diones is described based on a low-cost and environmentally benign KF/Al2O3 and PEG-400 co-catalyst catalyst via open-ring reactions of 2,4,6- triarylpyrylium salts compounds under microwave irradiation conditions. The advantage of this method is satisfactory yields, short reaction time and the use of a cheaper, milder, and efficient catalyst. Finally, twelve α, β- unsaturated diones have been obtained in good to excellent yields by this procedure.

Using cuprous iodide as the catalyst, aryl halides reacted with phenols to form diaryl ethers. The reaction conditions were optimized: aryl halides (1 equiv) reacted with phenol (1 equiv) at 130 °C in DMF for 16 h with cuprous iodide (10 mol %), cesium carbonate (2.5 equiv) as the base, and tetramethylenediamine (5 mol %) as the ligand. Under the optimum conditions, reaction conversion with time was summarized. The structural parameters of four types of aryl halides and the ionization energy of various C-X bond lengths in all aryl halides-CuI π-complexes were calculated at the B3LYP/LANL2MB level by using the Gaussian 03 program and the corresponding Ullman reaction conversion was determined by HPLC. Results suggested that different relationships existed between reactivity and the energy of the lowest unoccupied molecular orbital ELUMO, mean polarizability α and dipole moment μ. Both experimental and theoretical results, all displayed Ullman coupling reactivity order of the four aryl halides: fluorobenzene << chlorobenzene < bromobenzene < iodobenzene.

Isonitrile derivatives have been synthesized in good to high yields by dehydration of aliphatic and aromatic formamides in the presence of benzene-1,3-disulfonyl dichloride as easy and efficient reagent.

Highly effective microwave-assisted palladium-catalyzed arylation of styrenes and alkenes with diaryliodonium salts have been developed, giving styrenes in high yields without ligand in 60 s.

A general synthetic route to synthesis of N-cyclohexyl-3-aryl-quinoxaline-2-amines has been developed using ZnO nanoparticles under mild conditions. The multi-component reactions of aldehydes, o-phenylenediamine and cyclohexyl isocyanide were carried out to afford some N-cyclohexyl-3-aryl-quinoxaline-2-amines derivatives. The present approach offers several advantages such as high yields, environmentally benign, easy purification, recovery and reusability of the catalyst.

Eight dendritic polyphenols (generation1) of hydroxy benzoic and hydroxy cinnamic acids were synthesized in good overall yields using Mitsunobu reaction and BOP coupling agent and their antioxidant activities including radical scavenging activity were studied by cyclic voltammetry. Antioxidants with strong free radical scavenging abilities and devoid of prooxidant effects would be of immense biological importance. Therefore to minimize prooxidant effects and to increase free radical quenching properties, the dendrimers were designed with metal chelating compounds as core and with a periphery, rich in phenolic hydroxyl groups, benzylic hydrogens and electron donating ring substituents.

A convenient method for the synthesis of organic carbamates of 2-aminopyridine without using hazardous chloroformate reagent is developed. This alternate approach for the synthesis of organic carbamates and their alkylation to 2-alkylaminopyridines is more practical and economical to be used on large scale. The amazing behavior of 2- aminopyridine helps in forming organic carbamates unlike 3-aminopyridine and 4-aminopyridine.

Amphidinolide E is a 19-membered macrolide possessing potent cytoxic activity. The macrolide core having two key intermediates alcohol and acid was synthesized efficiently. The THF ring segment was synthesized from Dglucose as chiral precursor, whereas the cis-tetrahydrofuran ring was established by stereoselective intramolecular oxymercuration reaction. The acid component having E-diene was established by Stille cross coupling of vinyl iodo and vinly stannane segment. Coupling reaction of acid segment and alcohol was examined.

Facile and green syntheses of potential analgesic and antipyretic compounds, N-(4-ethoxy-phenyl)-2-(1,3- dioxo-1,3-dihydroisoindol-2-yl)acetamide derivatives 6a-g and N-[(4-ethoxy-phenylcarbamoyl)methyl]phthalamic acid derivatives 10a-g have been developed. Two synthetic routes (A and B) have been established for the preparation of 6a-g. In the route-A, 4-ethoxyaniline 2 was reacted with chloroacetyl chloride 3 in a solution of potassium acetate and acetic acid to yield N-(4-ethoxyphenyl)-2-chloroacetamide 4. The latter was reacted with imide compounds 5a-g either in triethanolamine as a green solvent or in solid phase in the presence of TEBAC and KI to yield 6a-g. Alternatively, in the route-B, reaction of anhydrides 7a-g with glycine 8 yielded the (1, 3-dioxo-1, 3-dihydroisoindol-2-yl)acetic acid derivatives 9a-g which on reaction with 2 either in triethnolamine and DCC as a dehydrating agent or in solid phase in the presence of DCC gave 6a-g. The latter were hydrolyzed in 0.5N ethanolic KOH to afford 10a-g.