Letters in Organic Chemistry - Volume 11, Issue 3, 2014

In this work, a novel polymer namely poly(N,N'-dibromo-N-ethylnaphthyl-2,7-disulfonamide) (PBNS) is synthesized and characterized by studying its IR, 1H NMR, 13C NMR and thermal gravimetric analysis (TGA). This polymer is utilized as a highly efficient, heterogeneous and recyclable N-bromo reagent to catalyze acetylation of various compounds such as alcohols, phenols, thiol and amine with acetic anhydride under solvent-free conditions, and also it worthily catalyzes deacetylation of acetate esters in aqueous media.

N',N"'-[2,2'-[[1,1'-Biphenyl]-4,4'-diylbis(oxy)]bis(acetyl)]di(benzohydrazide) 3 was prepared by reaction of 2,2'-[1,1'-biphenyl]-4,4'-diylbis(oxy)]bisacetohydrazide 2 with benzoyl chloride. A new series of the arylidene 4-15 was prepared by heating 2 with the following aldehydes: 4-flourobenzaldehyde, p-tolualdehyde, 2-hydroxy-3- methoxybenzaldehyde, 2-chlorobenzaldehyde, isonicotinaldehyde (4-pyridine carboxaldehyde), benzaldehyde, 4- chlorobenzaldehyde, picolinaldehyde (2-pyridine carboxaldehyde), 4-methoxybenzaldehyde (4-anisaldehyde), 3- bromobenzaldehyde, 2,4,6-trimethoxybenzaldehyde and 4-hydroxy-3-methoxybenzaldehyde (vaniline). The compounds were evaluated against influenza virus. Two compounds showed moderate activity which means that with more derivatization, better activity could be expected.

This study describes the synthesis of novel 4-nitro-2-substitutedimidazole derivatives via a transposition reaction of nitro group. Conversion of 5-nitro-2-phenylethanol (styryl) imidazole derivatives into the corresponding 4- nitroisomers was achieved in good yields in nitrobenzene using a catalytic amount of methyl iodide. Spectroscopic study and single crystal X-ray structures are reported for five compounds to understand the conformational structures of these compounds.

An efficient synthesis of 2-substituted benzoxazoles via copper acetate monohydrate oxidative coupling of aldehydes with o-aminophenol is described. This synthetic strategy has some advantages as simple procedure, inexpensive and easily available catalyst, and facile isolation of the products in moderate to good yields.

N-Substituted 8-hydroxybenzo[g]chromeno[4,3-b]indol-6(13H)-ones have been efficiently synthesized via a Nenitzescu reaction of naphthoquinone (or benzoquinone) and N-substituted 4-aminocoumarins in the presence of a catalytic amount of KHSO4 with a [bmim][BF4]/toluene system.

The synthesis of (+/-)-neuchromenin, a known natural product that induces neurite outgrowth of PC12 cells, is described. The total synthesis involved constructing a chromone ring from sesamol and coupling this intermediate to an aldehyde by a Morita-Baylis-Hillman reaction (MBH). The MBH adduct was cyclized under acidic conditions followed by removal of a methylene group to afford (+/-)-neuchromenin in 9 steps from sesamol.

The carbon-carbon bond formation by the condensation of bisulfite adduct of aromatic aldehydes with thiazolidine-2, 4-dione to furnish 5-arylidene-2,4-thiazolidinedione’s has been investigated. This novel methodology was applied to convert substituted aryl bisulfite adducts to corresponding 5-arylidene-2,4-thiazolidinedione’s with POCl3 in less-polar solvents such as toluene, chlorobenzene and o-xylene. 5-(4-methoxybenzylidene)thiazolidine-2,4-dione and 5-(4-ethoxybenzylidene)thiazolidine-2,4-dione were obtained in good yields.

Two heterogeneous catalysts based on 12-tungestocobaltic acid, including K5CoW12O40 and H5CoW12O40 supported on rice husk ash extracted nano silica (CoW/NSiO2), were used in selective alkylation of arenes with benzhydrol (diphenylmethanol). CoW/NSiO2 exhibited the highest activity. Thus, it was selected as the best choice for the synthesis of various triarylmethanes. This catalyst could be recycled by simple filtration and reused several times without any regeneration. Short reaction time, excellent yield and ease of catalyst recovery with consistent activity make this protocol efficient and environmentally benign.

An efficient synthetic route to prepare two new HYNIC derivatives with a 2-nitroimidazole moiety designed for tumor hypoxia imaging is described. During the course of the synthesis, the optimization of N-alkylation reaction of 2- nitroimidazole with propargyl bromide is reported to favor the formation of the terminal alkyne versus allene. Thereafter, the two ligands were used with tricine/EDDA to complex99MTc. However, decomposition of these ligands was observed and we suggest a reasonable explanation based on LC-MS analysis.

Dicoumarols, derived from aldehydes with ortho hydroxy substitution (5 and 7), were successfully cyclized by Sn(n-Bu)3Cl in THF as a reaction medium. Catalytic cycle reveals the formation of HO-Sn-O=C cyclic intermediate which is rearranged and isomerized to the cyclic lactone. N-butane was released by Sn(n-Bu)3Cl leaving behind Sn(n- Bu)2(OH)Cl keeping the catalytic route continued unless the two butane attached to tin were also consumed. The products produced were characterized using 1H, 13C{1H}-NMR, high resolution EI-MS, IR and elemental analyses. Single crystals of 6 were grown in P1 space group from concentration in THF and structurally studied using X-ray diffraction analysis. All the spectroscopic and analytical studies supported the formation of the cyclized products.

The thermal [3+2] cycloaddition reaction of N-acyliminophenanthridinium betaines with various allenoates has been investigated. The reaction was operationally simple and proceeded smoothly under mild reaction conditions, providing a variety of aromatic tetracyclic heterocycles in moderate to excellent yields.

Baker-Venkataraman (BV) rearrangement is the method of choice for the synthesis of flavones. The major limitation of BV is that it requires extensive protections and deprotections of hydroxyl groups which make the process lengthy and cumbersome. In the present study, a three step efficient method has been developed using simple protecting groups and easily available starting materials. New syntheses for acacetin, chrysoeriol, diosmetin, tricin and other hydroxylated flavones are described.

A phototrigger, 1,2,2-triphenylethanone (TPE), was synthesized for the photorelease study. The photorelease of 1,2,2-triphenylethanonyl N-t-Boc-γ-amino glutamate (TPE- N-t-Boc-GABA) showed the quantum efficiency of φ = 0.75. The phototrigger underwent further transformations that yielded Benzo[b]phenanthro[9,10-d]furan (9).