Letters in Organic Chemistry - Volume 11, Issue 2, 2014

An efficient method has been developed for the synthesis of substituted 1,5-benzoxazepines and benzothiazepines under classical heating conditions or microwave irradiation in the presence of an efficient and reusable Potassium Dodecatungstocobaltate Trihydrate (PDTC, K5CoW12O40.3H2O) as heterogeneous catalyst which was found to be highly active and afforded excellent yields. The products 6,8,9 and 10 were synthesized using the starting compounds 4a-d, 1 mol% PDTC and achieved in good yields by reflux (70-80%) as well as microwave conditions (60-70%). The reactions of 17a-e with 7, in the presence of 1 mol % PDTC were refluxed in dry ethanol for 6-8 h to isolate the compounds 18a-e in good yields (70-85%) as syrups.

Niobium pentachloride catalyzed one-pot multicomponent condensation reaction of β-naphthol, aryl aldehydes and cyclic 1,3-dicarbonyl compounds. Thus, a variety of 8,9,10,12-tetrahydrobenzo[a] xanthen-11-one derivatives were produced in good to excellent yields.

The present study describes the Bi (III) chloride catalyzed transformation of 4'-hydroxy-3',5'-dinitrochalcones into the corresponding benzoxazepines followed by sequential Michael addition using Bi (III) oxychloride as a procatalyst efficiently.

The reaction of aromatic aldehydes with thiosemicarbazide gives arylidene hydrazinecarbothioamide, whose reaction with phenacyl bromide, yielded (arylidenehydrazonyl)-4-phenylthiazole. The structures of 3 and 7 were fully characterized by using 1H-NMR and mass spectroscopic techniques. The spectral analysis agreed with the assigned structures. The assigned structures were further supported by single-crystal X-ray diffraction studies and summarized as follows: (3) Triclinic, P-1, a=7.6319(4) Å, b= 8.7099(4) Å, c=10.7145(5) Å, α= 77.7400 (10)°, β= 74.0160 (10)°, and γ= 72.8270 (10)°, V= 647.47(5) Å3, and Z = 2; (7) Orthorhombic, Pna21, a = 9.3760(13), b = 14.029(2), c = 23.591(3)Å, α=90, β= 90, and γ= 90o, V = 3103.0(7)Å3, and Z = 4.

Microwave-assisted organic synthesis (MAOS) for dibenzo-substituted crown ethers is presented. Two routes were developed: (1) one-pot MAOS for symmetric dibenzo-crown ethers (DBC) and (2) a two-step MAOS via diphenol intermediates for both symmetric and asymmetric DBCs. MAOS were carried out in open or closed vessels, with or without temperature control at various microwave settings using different bases and reactants. Open vessel MAOS was limited by the volatility of reactants hence was less preferred than the closed vessel MAOS. DBC formation was highly affected by the cation size of the base, which acted as a template ion during DBCs ring closure. Closed vessel MAOS without temperature control was found most appropriate for DBC synthesis. Symmetric DBCs were conveniently obtained via one-pot MAOS whereas asymmetric DBCs were obtained from two-step MAOS via diphenol intermediates. The method was found expedient as it afforded satisfactory yields at considerably shorter reaction time than those in conventional methods.

Six metal complexes were synthesized from Cd (II), Mn (II) and Zn (II) chloride and ligands 2-((3- nitrophenylimino)methyl)phenol (HL1) and 2-((4-nitrophenylimino)methyl)phenol (HL2) in 1:2 M ratio. Microanalytical data, UV-Visible spectral data, magnetic susceptibility, IR, 1HNMR, 13CNMR, mass and molar conductance measurements were used to characterize the structure of complexes. The complexes were found to be non electrolytic on the basis of molar conductance studies. The Schiff bases and their metal complexes had also been screened for their antinemic activity against root knot nematode, Meloidogyne incognita. Complexes have shown significant antinemic activity than their corresponding Schiff bases.

A chemoselective synthesis of 7-amino-5-aryl-2-hydroxy-3-(aryldiazenylpyrazolo[1,5-a]pyrimidine-6- carbonitriles and 4-((7-amino-6-cyano-2-hydroxy-5-arylpyrazolo[1,5-a]pyrimidine-3-yl)diazenyl)benzenesulfonamides through three-component reaction of 3-aminopyrazoles, aldehydes and malononitrile in the presence of base catalysts such as sodium acetate, pyridine and high surface area MgO is reported. 3-Amino pyrazoles were prepared by refluxing of ethyl(arylazo) cyanoacetates with hydrazine hydrate in ethanol. Structures of the new compounds were established by their spectral data and theoretical results. Density Functional Theory (DFT) calculations have been performed to optimize the structure of products. The theoretical results are in good agreement with experimental findings. The theoretical results are compared with the experimetal data. DFT calculations reveal that the enol form of 6 is the most stable molecule.

A catalyst-free multi-component synthesis of spiro[indoline-3,4’-pyrano[2,3-c]pyrazoles] is reported from in situ formed pyrazolone by exothermic reaction of ethyl acetoacetate with hydrazine hydrate, isatin and malononitrile in water at room temperature. A suggested mechanistic approach was supported by semi-empirical calculations. The transformation is carried out in water alone and thus achieved the highest level of green chemistry. Simple reaction conditions, easy work-up procedure and isolation of products are the auxiliary advantages of present protocol.

An efficient and new method for the copper-catalyzed cyanation of aryl halides is reported using a new oxazole ligand and K4Fe(CN)6 as a non-toxic source of cyanide.

The stereoselective synthesis of an antifungal drug, Terbinafine, bearing (E)-tert-butylenyne structural element as the side chain is achieved by coupling N-methyl-1-napthalene methanamine with 1-bromo-6,6-dimethyl-2E-hepten-4- yne in good yield. The new methodology avoids the use of toxic starting materials like acrolein and phosphorous pentachloride that were used in earlier reports. The structure was confirmed by IR, NMR, MS, and elemental analysis.

A new series of 1-substituted 1H-1,2,3,4-tetrazoles was synthesized from the reaction of L-α-amino acids, triethylorthoformate and sodium azide in glacial acetic acid at 80 °C in good yields (55-80 %). Not only acetic acid is a good solvent but also an effective catalyst promoting the reaction compared with the Lewis acids/microwave, Lewis acids/ ultrasonic or Lewis acids/solvent-free conditions to give the corresponding 1H-1,2,3,4-tetrazoles. Also, the antimicrobial activity investigations (antibacterial activity against E. coli and antifungal activity against Candida albicans) showed that all the tetrazoles obtained were inactive except the one obtained from tryptophan. In addition, the obtained 1- substituted 1H-1,2,3,4-tetrazoles were resistant in different reducing and oxidizing conditions.

M/Y zeolites (M = Cu (II), Ni (II) and Co (II)) were synthesized by microwave solid state and aqueous solution ion-exchange methods. Then, these compounds were prepared in nano scale. Copper(II) nitrate, cobalt(II) nitrate, zeolite Y, nano-sized zeolite Y and all of nano-sized M/Y zeolites were used as acidic catalysts for the synthesis of 2-[(5-Chloro- 2-hydroxy-phenylimino)-methyl]-4-(4-nitro-phenylazo)-phenol (2a) as a model reaction and homogenous catalysts were compared to heterogeneous catalysts. The solid state ion-exchanged zeolites showed higher activity in comparison to aqueous solution ion-exchanged zeolites and Co was selected as the best metal. The amount of catalyst was optimized and nano-sized solid state ion-exchanged Co/Y zeolite was reused for three times. Finally, other derivatives of Schiff bases based on azo were synthesized by nano-sized solid state ion-exchanged Co/Y zeolite and yields were reported. The structure of 2a-j was confirmed using elemental analysis, 1H-NMR and FT-IR spectroscopy.