(η6-Arene)chromium complexes in organic synthesis: [2,3]-Wittig rearrangement of (benzyl crotyl ether)chromium complexes

The [2,3]-Wittig sigmatropic rearrangement of (benzyl (E)-crotyl ether)chromium complexes is shown to give a syn stereoselection which is different from the anti selection reported for the corresponding chromium-free compounds.     

Enantioselective synthesis of 1-nitrotricyclo[5,2,2,02,6]undeca-3,8-dienes via tandem consecutive asymmetric Diels–Alder reaction–Cope rearrangement

The 1-glyco-2-nitrocyclohexa-2,4-dienes 1a and 5a react with cyclopentadiene to yield, almost exclusively, the 10-glyco-1-nitrotricyclo[5,2,2,0^2,6]undeca-3,8-dienes 4a and 8a. Formation of these products is explained as the result of a tandem consecutive asymmetric Diels–Alder reaction–Cope rearrangement. Periodate oxidation of deprotected sugar side-chains, followed by sodium borohydride reduction yielded enantiomerically pure 10-formyl- and 10-hydroxymethyl-1-nitrotricyclo[5,2,2,0^2,6]undeca-3,8-dienes. Structures have been determined by X-ray crystallographic and spectroscopic analyses, and chemical correlation.     

Construction of new heteroacenes based on benzo[b]thieno[2,3-d]thiophene / quinoline or 1,8-naphthyridine systems using the Friedländer reaction

Two new classes of heteroacenes, namely benzo[4′,5′]thieno[2′,3′:4,5]thieno[3,2-b]quinolines and benzo[4′,5′]thieno[2′,3′:4,5]thieno[3,2-b][1,8]naphthyridines, have been formed using the Friedländer reaction to annulate the benzo[b]thieno[2,3-d]thiophene scaffold to quinoline or 1,8-naphthyridine fragments. In accordance with this synthetic strategy, benzo[b]thieno[2,3-d]thiophen-3(2H)-ones were treated with 2-aminobenzaldehydes or 2-aminonicotinaldehyde in the presence of pyrrolidine in glacial acetic acid at reflux to give the desired quinoline- or 1,8-naphthyridine-fused compounds, respectively. The optical and electrochemical properties of selected heteroacenes were determined.     

Regio- and diastereoselective synthesis of new functionalized indolo[2,3-b]indole-pyrimidine based on C–N bond formation via a four-component reaction

A facile and diastereoselective synthetic procedure has been designed for the preparation of new substituted indolo[2,3-b]indole (IDID) moiety at position-5 of the pyrimidine ring by a one-pot four-component reaction of dimedone, aniline and substituted derivatives, barbituric acid/thiobarbituric acid and isatin under mild conditions. This method proceeds rely on a CsbndN bond formation under catalyst-free conditions affording a range of skeletally diversity 5-indolo[3,2-b]indole-pyrimidine-based heterocycles. 5-Indolo[2,3-b]indol-pyrimidine-2,4,6-trione and 5-indolo[2,3-b]indol-2-thioxo-pyrimidine-4,6-dione were obtained in EtOH solvent in high yield, short reaction time and diastereoselectivity. The structural diversities of the synthesized compounds have been confirmed spectroscopically, by IR ¹H- and ¹³C NMR, EI-MS spectra and elemental analyses which agree with the proposed structures.     

Asymmetric copper-catalyzed Diels–Alder reaction revisited: control of the structure of bis(oxazoline) ligands

Synthesis of 1,4-bis(oxazoline) ligands bearing a bicyclo[2,2,2]backbone derived from 9,10-dihydro-9,10-ethanoanthacene trans-dicarboxylic acid was revisited. Starting from l- or d-amino alcohols and either (S,S) or (R,R)-dihydroethano trans-dicarboxylic acid, a complete series of ligands was evaluated in the copper-catalyzed Diels–Alder reaction. The most efficient ligands with a phenyl substituent on the oxazoline ring afforded enantiomeric excess up to 98%. This is different from previous results indicating that the best enantioselectivity involved a diastereomeric ligand with the meso-backbone.     

Spectrofluorimetric determination of formaldehyde by a flow-injection method based on its catalytic effect on the acridine yellow–bromate reaction

A flow-injection configuration for the determination of formaldehyde is proposed. The method is based on the enhancing effect of formaldehyde on the oxidation of acridine yellow by bromate in acidic medium. The proposed procedure is simple, inexpensive, sensitive and suitable for concentrations of formaldehyde between 1 and 56 microg mL(-1). A sampling-rate of 60 samples h(-1) was achieved. The effect of several organic and inorganic species was studied. The method was applied to the determination of formaldehyde in pharmaceuticals, milk and air in work environments. The accuracy of the method was confirmed by comparing the results with those obtained using the standard acetylacetone method.     

Synthesis of pyrazolo[3,4-b]pyrrolo[3,4-d]pyridine derivatives via Aza-Diels–Alder reaction: evaluation of torsion effect of pyrazoylimines

A modified method for the synthesis of pyrazolo[3,4-b]pyrrolo[3,4-d]pyridine was developed through an Aza-Diels–Alder reaction of pyrazoylimines with maleimides in the sealed tube. Based on the control experiment, the yields for the Aza-Diels–Alder reaction seemed proportional to the suitable torsion conformation of pyrazoylimine, which was modulated by N,N-disubstituted amidinyl moiety. The versatile sealed tube technique was also proved to promote the higher isolated yields in the Aza-Diels–Alder reaction.     

Half-sandwich η-arene–ruthenium(II) complexes bearing 1-alkyl(benzyl)-imidazo[4,5-f][1,10]-phenanthroline (IP) derivatives: the effect of alkyl chain length of ligands to catalytic activity

The reaction of bromoalkanes (R–Br; (3), R=C_nH_2n+1, n=4 (a), 8 (b), 12 (c),18 (d)) and bromobenzyl derivatives (R′–Br; (4), R′=CH₂C₆H₂(CH₃)₃-2,4,6 (a); CH₂C₆H(CH₃)₄-2,3,5,6 (b); CH₂C₆(CH₃)₅ (c)) with 1H-imidazo[4,5-f][1,10]-phenanthroline (IP)(L₂) gave the corresponding 1-R-imidazo[4,5-f][1,10]-phenanthroline (IPR)(L_3a–d) and 1-R′-imidazo[4,5-f][1,10]-phenanthroline(IPR')(L_4a–c) ligands, respectively. Treatment of L_3a–d and L_4a–d with [Ru(p-cymene)Cl₂]₂ led to the formation of [Ru(p-cymene)(IPR)Cl]Cl (RuL_3a–d) and [Ru(p-cymene)(IPR′)Cl]Cl (RuL_4a–c). New ruthenium(II) complexes RuL_3a–d and RuL_4a–c were characterized by elemental analysis, FTIR, UV–visible and NMR spectroscopy. In order to understand effects of these changes on the N-substituent of imidazol on IP and how they translate to catalytic activity, these new RuL₂, RuL_3a–d and RuL_4a–c were applied in the transfer hydrogenation of ketones by 2-propanol in presence of potassium hydroxide. The activities of the catalysts were monitored by NMR and GC analysis.     

Catalytic effect of calix[n]arene based sol–gel encapsulated or covalent immobilized lipases on enantioselective hydrolysis of (R/S)-naproxen methyl ester

In this paper the catalytic performance of the immobilized lipases was investigated in the presence of calixarene based polymers using different immobilization techniques. For this reason, Candida rugosa lipase was encapsulated in sol–gel matrices using alkoxysilane precursors and calix[n]arene based silica polymers as additives. The hydrolytic activities of encapsulated lipases were evaluated and compared with the free lipase and covalently immobilized lipases (CnP-L). These encapsulated lipases were also used in the kinetic resolution of the R/S-Naproxen methyl ester. The results indicated that the C6P encapsulated lipase has significantly higher conversion and enantioselectivity as compared to the free lipase; other encapsulated lipases and CnP-L. The optimal pH and temperature region of the C6P encapsulated lipase in the kinetic resolution of the R/S-naproxen methyl ester were 7.0 and 55?°C. Nevertheless, the encapsulated lipases have good stability, adaptability and reusability in comparison with the free enzyme.     

Triaryl- and trialkylantimony(V) Bis(catecholates) based on 1,1′-spirobis[3,3-dimethylindanequinone-5,6]: Spectroscopic and electrochemical studies

A series of new binuclear bis(catecholate) antimony(V) complexes based on 1,1′-spirobis[3,3-dimethylindanequinone-5,6] with various substituents at the central antimony atoms, R₃Sb(Cat-Spiro-Cat)SbR₃ (I–IV) and R₃Sb(Cat^Br-Spiro-^BrCat)SbR₃ (V–VIII) (R = p-fluorophenyl, phenyl, p-tolyl, and ethyl), were synthesized. Spirobis(catecholates) I–III exhibit two one-electron oxidation waves on the cyclic voltammograms, whereas bromo-substituted spirobis(catecholates) V–VII undergo two-electron oxidation immediately at the first stage. The two-electron oxidation of the complexes results in the loss of one of the organoantimony fragments and the formation of mononuclear catecholate-quinone complexes (Q-Spiro-Cat)SbR₃ or (Q^Br-Spiro-^BrCat)SbR₃, respectively. An insignificant delocalization of the charge and spin between two redox centers is observed in the complexes. The nature of substituents at the antimony atom exerts an effect on the values of redox potentials of the complexes: more donating groups decrease the oxidation potentials of the catecholate fragments and more withdrawing groups increases these values.     

New sigmatropic sequences based on the [2,3]-wittig rearrangement of the bis-allylic ether system : A general approach to regiocontrolled c—c bond formation of allylic moieties leading to unsaturated carbonyl compounds

Four new sigmatropic sequences triggered by the regiocontrolled [2,3]-Wittig rearrangement of unsymmetrical bis-allylic ethers (1) to the l,5-dien-3-ols (2) arc described, which provide unique, regiocontrolled methods for the synthesis of a wide variety of unsaturated carbonyl compounds possessing interesting molecular frameworks. The newly developed sequences include the [2,3]-Wittig-Claisen, the tandem [2,3]-Wittig-oxy-Cope, the tandem oxy-Cope-Claisen, and the tandem oxy-Cope-Cope sequences.     

Iodine/CuI-mediated alkyne–carbonyl metathesis reaction: synthesis of 1-aryl-1,2-dihydrochromeno[2,3-b]azepine-3,6-dione

Iodine/cuprous iodide-mediated intramolecular alkyne–carbonyl metathesis reaction has been developed using 2-(N-aryl-N-propargyl)aminochromone-3-carbaldehyde as the substrate. It led to the synthesis of hitherto unreported chromeno[2,3-b]azepine-3,6-dione. The special features of this methodology are mild reaction conditions, 100% atom economy and use of inexpensive reagents. This is the first example of I₂/CuI-mediated alkyne–carbonyl metathesis reaction.     

Dramatic lithium chloride effect on the reaction stereocontrol in Zn-mediated asymmetric cinnamylation: highly practical synthesis of β-aryl homoallylic amines

An extremely mild and practical approach for the preparation of enantiomerically enriched β-aryl substituted homoallylic amines bearing two adjacent stereogenic centers was realized by room temperature zinc-mediated highly stereoselective cinnamylation of N-sulfinyl imines.     

The effect of complexing agents on the DMF–chromium(VI) reaction. A kinetic study

The kinetics of the reduction of chromium(VI) by dimethylformamide (DMF) in the presence of ethylenediaminetetraacetic acid (EDTA) and 2,2-bipyridyl (bpy) was investigated in aqueous HClO₄ acid solutions spectrophotometrically. The experimental findings, that the reaction has an induction period followed by autoacceleration, is explained. After the reduction, chromium(III) is present as the EDTA- and bpy-complexes, although such complexes form very slowly under the same experimental conditions from chromium(III) and the EDTA and bpy, respectively. Increases in the reaction rate with increasing [EDTA] were observed, while added bpy had negligible effect on the reaction rate. The reaction is first-order each in [Cr^VI] and [H⁺]. The first-order kinetics with respect to EDTA at low concentrations shift to zero-order at higher concentrations. The reaction is considered to proceed through the formation of a very stable chromium(VI)–DMF–EDTA complex. The suggested mechanism refers only to the induction period of the reaction. The net rate of oxidation of DMF, as measured by the consumption of chromium (VI), is given by: –d[Cr^VI]/dt = kK ₁ K _b[H⁺][DMF]_T[EDTA][Cr^VI]_T/(1 + K ₁[EDTA])(1 + K _b[H⁺])     

Synthesis of novel spiro[benzo[4,5]thiazolo[3,2-a]chromeno[2,3-d]pyrimidine-14,3′-indoline]-1,2′,13(2H)-triones via three component reaction

A new and efficient method for the synthesis of hitherto unreported spiro[benzo[4,5]thiazolo[3,2-a]chromeno[2,3-d]pyrimidine-14,3′-indoline]-1,2′,13(2H)-triones was developed via the Domino Knoevenagel condensation–Michael addition–intermolecular cyclization sequences of isatin derivatives, cyclohexane-1,3-diones, and 2-hydroxy-4H-benzo[4,5]thiazolo[3,2-a]pyrimidin-4-ones, employing 12-tungstophosphoric acid (H₃PW₁₂O₄₀) as an effective and inexpensive catalyst.     

One-pot synthesis of 6H-pyrrolo[2,3-e[1,2,4]triazolo[1,5-a]pyrimidines on the basis of σH-adducts of 6-Nitro[1,2,4]triazolo[1,5-a]pyrimidine with carbonyl compounds

Aromatic, heteroaromatic, and aliphatic carbonyl compounds reacted with 6-nitro[1,2,4]triazolo[1,5-a]pyrimidine in the presence of a base to give stable σ^H-adducts at C⁷. Reduction of the nitro group in the latter is accompanied by tandem autoaromatization of the azine ring and intramolecular cyclocondensation with formation of the corresponding 6H-pyrrolo[2,3-e][1,2,4]triazolo[1,5-a]pyrimidines. Original Russian Text ? E.B. Gorbunov, G.L. Rusinov, R.I. Ishmetova, V.N. Charushin, O.N. Chupakhin, 2008, published in Zhurnal Organicheskoi Khimii, 2008, Vol. 44, No. 1, pp. 130–134. Dedicated to Full Member of the Russian Academy of Sciences G.A. Tolstikov on his 75th anniversary     

First total synthesis of (±)-floribundane B: An approach based on Johnson-Claisen rearrangement of a Morita-Baylis-Hillman adduct

The first total synthesis of (±)-floribundane B is reported. Johnson-Claisen rearrangement of a Morita-Baylis-Hillman adduct assembled all of the stereochemical features of this secoiridoid. The formal synthesis of (±)-oleocanthal and the synthesis of a chemical constituent of olive press juice is also reported.