Catalyst-free facile and efficient one-pot synthesis of densely functionalized pyrroles and α-amino ketones

An efficient catalyst-free one-pot three-component synthesis of penta-substituted pyrroles has been successfully developed. A variety of penta-substituted pyrroles were straightforwardly synthesized from good to excellent yields (78%–93%) by using easily accessible starting materials under mild conditions. This protocol also provided α-amino ketones in good yields (87%–98%) without column chromatography.     

Design,synthesis, and biological activity studies of a new class of sulfonated aurones: First synthesis of acidoaurone isolated from Phyllanthus acidus

A novel series of aurones were designed by introducing sulfonic acid group on ring-A and ring-B of known natural aurones such as hispidol, sulfuretin, maritimetin, and aureusidin. These sulfonated aurones were synthesized by a unique approach. Sulfonation on ring-A or ring-B converts water-insoluble aurones into highly water-soluble aurones. The sulfonated aurones were tested for their antioxidant, antiinflammatory, and AChE inhibition activities along with their natural aurones. Ring-A sulfonated aurones displayed higher antioxidant activity, 5-LOX, and AChE inhibition in comparison with their corresponding natural aurones. Ring-B sulfonated aurones exhibited potent 5-LOX inhibitory activity and significant antioxidant activity. Acidoaurone, a first sulfonated aurone isolated from Phyllanthus acidus was synthesized for the first time and was well characterized using NMR, LC–MS, and further confirmed by HMBC.     

Studies in the formation of heterocyclic rings containing nitrogen

Synthesis of 1-benzyl-3-methyl (I), 1-beazyl-3-substituted benzyl (II) and 1-methyl-3-substituted benzyl (III)-2-aryl benzimidazolines is described. (I) acc obtained by the condensation of N¹benzyl-N²methyl-o-phenylenediamine with various aldehydes in metharol. Compounds (II) are prepared from N¹-benzyl-N²-arylidene-o-phenylenediamines in acetic acid, through a process of disproportionation involving an oxidation-reduction process. Likewise, (III) are obtained from N¹-methyl-N²-arylidenc-o-phenylenediamines. The exact structure of N¹-benzyl-N²-arylidene-o-phenylenediamines which can exist in the open chain form or in the ring form has been investigated using nmr spectroscopy.     

Iodine-catalyzed three-component one-pot synthesis of naphthopyranopyrimidines under solvent-free conditions

Iodine is found to be a highly efficient catalyst for the three-component coupling (3CC) of aldehydes, β-naphthol, and 1,3-dimethylbarbituric acid under solvent-free conditions to afford the corresponding 8,10-dimethyl-12-aryl-12H-naphtho[1′,2′5,6]pyrano[2,3-d]pyrimidine-9,11-diones in good yields with high selectivity. The use of readily available iodine makes this method very simple, convenient, and cost-effective.     

Cyclisation of 2-(2-aminophenyl)quinazolin-4(3H)-one reexamined: formation of isomeric angular fused quinazolinoquinazolinones and their spectroscopic identification

Cyclisation of 2-(2-aminophenyl)quinazolin-4(3H)-ones on to N₃ and on to N₁ leading to 6-alkyl-(8H)-quinazolino[4,3-b]quinazolin-8-one and 6-alkyl-(13H)-quinazolino[3,4-a]quinazolin-13-one, respectively was described for the first time. The differences in the IR and carbon NMR data of these isomeric fused quinazolinoquinazolinones afford a useful method for distinguishing between the two series.     

Data-, knowledge- and method-bases in chemical sciences I. BAQOR-database for equilibrium constants in aquo-organic media

BAQOR is a computer readable database for equilibrium constants in presence of different percentages of water miscible cosolvents. The present version with user friendly software in dBase III+ contains 740 records and runs on any IBM compatible PC. The physico-chemical properties of binary and ternary water-cosolvent mixtures, the equilibrium constants of proton- and metal-ligand complexes are retrievable through pop-up menus. Specific searches by metal-, ligand-, solvent-, and stoichiometry-wise and their combinations is possible. Several display modes-monitor, file and hard copy-are available for the numerical fields as well as for literature citation.     

A biogenetically patterned enantiospecific synthesis of allopupukeanones

The first enantiospecific synthesis of allopupukeanones has been accomplished starting from 6-methylcarvone. A biogenetically patterned rearrangement of a pupukeanane to allopupukeanane was employed as the key step.     

Synthesis and ion-exchange properties of zirconium molybdoarsenate (ZrMAs)

Zirconium molybdoarsenate (ZrMAs), an inorganic ion exchanger, has been synthesized and the suitable conditions to separate cesium-137 from fission products waste solution are suggested.     

Acid-catalyzed dehydration of naphthalene-cis-1,2-dihydrodiols: origin of impaired resonance effect of 3-substituents

Acid-catalyzed dehydrations of substituted naphthalene-cis-1,2-dihydrodiols occur with loss of the 1- or 2-OH group to form 2- and 1-naphthols, respectively. Effects of substituents MeO, Me, H, F, Br, I, and CN at 3-, 6-, and 7-positions of the naphthalene ring are consistent with rate-determining formation of β-hydroxynaphthalenium ion (carbocation) intermediates. For reaction of the 1-hydroxyl group the 3-substituents are correlated by the Yukawa-Tsuno relationship with ρ = -4.7 and r = 0.25 or by σ(p) constants with ρ = -4.25; for reaction of the 2-hydroxyl group the 3-substituents are correlated by σ(m) constants with ρ = -8.1. The correlations for the 1-hydroxyl imply a surprisingly weak resonance interaction of +M substituents (MeO, Me) with a carbocation reaction center but are consistent with the corresponding correlation for acid-catalyzed dehydration of 3-substituted benzene-cis-1,2-dihydrodiols for which ρ = -6.9 and r = 0.43. Substituents at the 6- and 7-positions of the naphthalene rings by contrast are correlated by σ(+) with ρ = -3.2 for reaction of the 1-hydroxyl group and ρ = -2.7 for reaction of the 2-hydroxyl group. The unimpaired resonance implied by these substituent effects appears to be inconsistent with a previous explanation of the weak resonance of the 3-substituents in terms of imbalance of charge development and/or nonplanarity of the benzenium ring in the transition state. An alternative possibility is that the adjacent hydroxyl group interferes sterically with conjugation of +M substituents. "Hyperaromaticity" of the arenium ion intermediates does not appear to be a factor influencing this behavior.     

Hyperaromatic stabilization of arenium ions: a remarkable cis stereoselectivity of nucleophilic trapping of β-hydroxyarenium ions by water

Cis- and trans-1,2-dihydrodiol isomers of benzene undergo acid-catalyzed dehydration to form phenol. In principle the isomeric substrates react through a common β-hydroxybenzenium (cyclohexadienyl) carbocation. Notwithstanding, the isomers show a large difference in reactivity, k(cis)/k(trans) = 4500. This difference is reduced to k(cis)/k(trans) = 440 and 50 for the 1,2-dihydrodiols of naphthalene and 9,10-dihydrodiols of phenanthrene, respectively, and to 6.9 for the dihydrodiols of the nonaromatic 7,8-double bond of acenaphthylene. Because the difference in stabilities of cis- and trans-dihydrodiols should be no more than 2-3-fold, these results imply a high cis stereoselectivity for nucleophilic trapping of a β-hydroxyarenium cation by water in the reverse of the carbocation-forming reaction. This is confirmed by studies of the 10-hydroxy-9-phenanthrenium ion generated from aqueous solvolyses of the trans-9,10-bromohydrin derivative of phenanthrene and the monotrichloroacetate ester of the phenanthrene cis-9,10-dihydrodiol. The cis stereoselectivity of forward and reverse reactions is explained by the formation (in the "forward" reaction) of different conformations of carbocation from cis- and trans-dihydrodiol reactants with respectively β-C-H and β-C-OH bonds in pseudoaxial positions with respect to the charge center of the carbocation optimal for hyperconjugation. Formation of different conformations is constrained by departure of the (protonated) OH leaving group from a pseudoaxial position. The difference in stability of the carbocations is suggested to stem (a) from the greater hyperconjugative ability of a C-H than a C-OH bond and (b) from enhanced conjugation arising from the stabilizing influence of an aromatic ring in the no-bond resonance structures representing the hyperconjugation (C(6)H(6)OH(+) ? C(6)H(5)OH H(+)). This is consistent with an earlier suggestion by Mulliken and a demonstration by Schleyer that the benzenium ion is subject to hyperconjugative aromatic stabilization. It is proposed that, in analogy with the terms homoconjugation and homoaromaticity, arenium ions should be considered as "hyperaromatic".