Letters in Organic Chemistry - Volume 9, Issue 9, 2012

The enzyme-mediated highly enantioselective hydrolysis of dicarboxylic acid monoesters was investigated. The racemic substrates, which were prepared by coupling of the corresponding alcohols with dicarboxylic anhydrides, were enantioselectively hydrolyzed by lipase from Candida antarctica (Novozym 435) in a buffer at 30 °C. The products were easily separated by a simple extraction procedure without laborious column chromatography to afford both enantiomers of the alcohols. We then determined that the dicarboxylic acid monoesters were suitable alternative substrates for the preparation of optically active alcohols.

A novel chiral dithiane alcohol ligand, based on chiral cyclopropane-backbone, was easily prepared from (–)- 1R-cis-caronaldehyde. The chiral ligand was used in asymmetric ethylation of aromatic aldehydes to afford the corresponding secondary alcohols with moderate to good enantioselectivity.

A practical and scalable synthesis of (Z)-9-tricosene, the sex pheromone of the housefly, has been achieved by the addition of one-carbon unit from the readily available (Z)-erucic acid. The synthesis is composed of three consecutive steps, lithium aluminium hydride reduction of erucic acid, tosylation of the resulting alcohol, and copper-catalyzed Kumada- type cross-coupling of the tosylate with methylmagnesium bromide as the key step. This approach is quite straightforward and capable of scale-up synthesis.

The synthesis of chiral esters and amides with the involvement of asymmetric induction by using pure chiral auxiliaries such as (1S, 2R, 5R) menthol and L-(+)-1-phenylethylamine is described. The chiral mono, di menthol esters and mono amides of succinic acid were synthesized in good yields. These esters and amides were then subjected to metalation and quenched with different alkyl halides to get α substitution to generate a new chiral center.

A series of 6-amino-4-aryl-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles (5a–5j) were synthesized by four-component one-pot reaction of methyl acetoacetate (or ethyl acetoacetate), hydrazine hydrate, arylaldehydes and malononitrile in the presence of phase transfer catalyst. A highest yield of product was obtained while using 30 mol % of HDBAC as a catalyst.

A series of chiral oxazolidines derived from (1R, 2S)-cis-1-amino-2-indanol was found to be effective in promoting the asymmetric addition of diethylzinc to aldehydes. Among the ligands developed, it was found that ligand 1b in the presence of Ti(OiPr)4 yielded the highest enantioselectivities when it was applied in the catalytic asymmetric addition of diethylzinc to aldehydes (up to 91% ee).

The intermolecular hydroamination of C-(tetra-O-acetyl-β-D- galactopyranosyl)allene with a variety of aromatic amines proceeded smoothly in the presence of gold(III) catalyst to afford the corresponding allylic amine in good yields. The reaction can be carried out at room temperature and under extremely mild conditions.

Proton conducting polyimides containing pendant benzimidazole groups have been synthesized by different ratios of 5-(1H-benzimidazol-2-yl)-benzene-1-3-diamine (DABI) and oxydianiline (ODA) in the presence of oxydianiline (ODPA). All the polymers were structurally characterized by Fourier transform infrared (FT-IR) spectroscopy while the thermal properties were studied by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). From application point of view, proton conductivity of all polymers doped with phosphoric acid was studied by impedance analyzer. All the polymers have been found to be thermally stable with high dielectric constants and are proton conductive. The polymer with highest DABI value showed highest conductivity (max 0.11 S/cm).

A green and efficient synthesis of novel 4-thiazolidinones 4 from cyclocondensation reaction of 2-(2,3-dihydro- 1H-carbazol-4(9H)-ylidene)hydrazinecarbothioamide 3 and α-haloacids catalyzed by N-methylpyridinium tosylate in quantitative yield is reported. Also, synthesis of new 2,4-disubstituted thiazoles 5 under grinding conditions is reported.

A series of novel pyrimido[4,5-b]quinoline-4,6(3H,5H,7H,10H)-dione derivatives was synthesized by one-pot three-component reaction of the appropriate aldehyde, dimedone or cyclohexanedione and 6-aminothiouracil in ethanol under ultrasonic irradiation at 50 oC in short reaction times (1.5-3 min) and excellent yields (94-99%). The antibacterial activities of the synthesized compounds were evaluated on M. leuteus, B. subtilis, E. coli and Ps. aeruginosa. All the synthesized products showed good antibacterial activities.

Chain 1,3-dicarbonyl compounds were firstly used as starting material to react with 5-amino-3-methyl-1- phenylpyrazol and aromatic aldehydes to prepare 1H-pyrazolo[3,4-b]pyridines in basic ionic liquid [bmim]OH. The onestep three-component reaction is simple and efficient. Additionally, water was the only one by-product during the whole process.

A series of mono- and bis-benzimidazolium and imidazolium salts of 4-pyrone derivatives has been synthesized in good yields, by various quaternization reactions of halomethyl derivatives of 4H-pyran-4-ones. These salts can be used as novel precursors of functionalized N-heterocyclic carbenes and some of them as novel ionic liquids.

Here we demonstrate the synthesis of various derivatives of 5-(6-substituted phenyl-2H-chromen-3-yl)- oxazoles 5(a-k) by using Suzuki coupling conditions with different substituted boronic acids and obtained 23-57 % yields. We also synthesised various derivatives of the 5-(substituted 2H-chromen-3-yl)-oxazoles 3(a-j) mediated by TOSMIC as a reagent and achieved 58-70 % yield.