Search

1,3-Dipolar cycloadditions of unsymmetrical C1-substituted 7-oxabenzonorbornadienes with acetonitrile oxide and benzonitrile oxide were investigated to probe the regio- and stereoselectivities of these reactions. All novel oxabicycle-fused isoxazoline adducts were obtained in moderate to excellent yields (53%-98%) and with complete exo-stereoselectivity. The major regioisomer in almost all instances showed positioning of the nitrile oxide's methyl or phenyl group anti to the C1-substituent. The relative ratios of the regioisomers suggested nonnegligible electronic and steric contributions of the C1-substituent in these reactions. Several useful applications of these 2-isoxazolines toward natural product synthesis are proposed via reductive cleavage of their N-O bonds. Key words: 1,3-dipolar cycloaddition, 7-oxabenzonorbornadiene, nitrile oxide, regioselective, 2-isoxazoline. Les cycloadditions 1,3-dipolaires de 7-oxabenzonorbornadienes asymetriques C1-substitutes en presence d'oxydes d'acetonitrile et de benzonitrile ont ete etudiees afin d'examiner la regioselectivite et la stereoselectivite de ces reactions. Tous les nouveaux adduits d'isoxazoline fusionnee avec un oxabicycle ont ete obtenus avec des rendements moyens a excellents (53 % a 98 %) et avec une exo-stereoselectivite totale. Le regioisomere majoritaire dans la plupart des cas a montre un positionnement anti du groupement methyle ou phenyle de l'oxyde de nitrile par rapport au substituant en C1. Les proportions relatives des regioisomeres ont mis en evidence les contributions electroniques et steriques non negligeables du substituant en C1 dans ces reactions. Plusieurs applications utiles de ces 2-isoxazolines dans la synthese de produits naturels sont proposees, et ce par clivage reductif de leurs liaisons N-O. [Traduit par la Redaction] Mots-cles: cycloaddition 1,3-dipolaire, 7-oxabenzonorbornadiene, oxyde de nitrile, regioselectif, 2-isoxazoline., Introduction 1,3-Dipolar cycloadditions of alkenes provide convenient onestep routes to the preparation of a variety of five-membered heterocycles. (1) Cycloadditions of alkenes with nitrile oxides are of paramount synthetic importance, [...]

The origin of stereoselectivity for [4+2] cycloaddition reaction of methyl methacrylate with cyclopentadiene was investigated with the B3LYP-D3(BJ)/6-31+G(d)//B3LYP/6-31+G(d) level of theory in the presence of the ionic liquid 1-ethyl-3-methylimidazolium chloride ([EMI.sup.+][Cl.sup.-]) and its acidic chloroaluminate melt, 1-ethyl-3-methyl-imidazolium heptachlorodialuminate ([EMI.sup.+][Al.sub.2][Cl.sub.7.sup.-]). The reaction of methyl methacrylate with cyclopentadiene was examined in the gas phase to rationalize the effect of the ionic liquid ion pairs [EMI.sup.+][Cl.sup.-] and [EMI.sup.+][Al.sub.2][Cl.sub.7.sup.-]. The DFT calculated results were found to be in good agreement with the experimentally observed results. The much-discussed hydrogen bonding effect of the imidazolium cation with the dienophile is less important to govern the stereoselectivity for the cycloaddition reaction. The atoms in molecules theory was used to examine the role of hydrogen bonding between the [EMI.sup.+] cation and methyl methacrylate in the transition state geometries. The calculated activation barriers with the M062X/6-31+G(d)//B3LYP/6-31+G(d) and MP2/6-311+G(d,p)//B3LYP/6-31+G(d) levels of theory also predict the similar exo/endo-stereoselectivity trend for the cycloaddition reactions. Key words: DFT, Diels-Alder reaction, cyclopentadiene, methyl methacrylate, ionic liquid. L'origine de la stereoselectivite de la reaction de cycloaddition [4+2] du methacrylate de methyle avec le cyclopentadiene a ete etudiee a l'aide du niveau B3LYP-D3(BJ)/6-31+G(d)//B3LYP/6-31+G(d) de la theorie de la fonctionnelle de la densite en presence du liquide ionique, le chlorure de 1-ethyl-3-methyl-imidazolium ([EMI.sup.+][Cl.sup.-]) et de son melange acide de chloroaluminate, le heptachlorodialuminate de 1-ethyl-3-methyl-imidazolium ([EMI.sup.+][Al.sub.2][Cl.sub.7.sup.-]). La reaction du methacrylate de methyle avec le cyclopentadiene a ete observee en phase gazeuse en vue de rationaliser l'effet des paires d'ions [EMI.sup.+][Cl.sup.-] et [EMI.sup.+][Al.sub.2][Cl.sub.7.sup.-] du liquide ionique. Les resultats de la TFD calcules ont montre une bonne concordance avec ceux obtenus experimentalement. L'effet de liaison hydrogene, souvent etudie, entre le cation imidazolium et dienophile influence peu la stereoselectivite de la reaction de cycloaddition. La theorie quantique des atomes dans les molecules a ete utilisee pour etudier le role de la liaison hydrogene entre le cation [EMI.sup.+] et le methacrylate de methyle dans les geometries d'etat de transition. Les barrieres de transition calculees a l'aide des niveaux M062X/6-31+G(d)//B3LYP/6-31+G(d) et MP2/6-311+G(d,p)//B3LYP/6-31+G(d) de la theorie permettent egalement de predire la meme tendance exo/endo-stereoselective des reactions de cycloaddition. [Traduit par la Redaction] Mots-cles: TFD, reaction de Diels-Alder, cyclopentadiene, methacrylate de methyle, liquide ionique., Introduction Traditional organic solvents that are generally volatile in nature can be replaced by ionic liquids (ILs) to avoid the emission of volatile organic compounds in our environment. (1) The [...]

Dipolar cycloaddition reactions allow for the efficient construction of five-membered heterocycles, often with diverse medicinal applications. We examined the 1,3-dipolar cycloaddition of 7-oxabenzonorbornadienes and 7-azabenzonorbornadienes with acetonitrile oxide and benzonitrile oxide, achieving an assortment of heterobicycle-fused isoxazolines with good to excellent yields. All isoxazolines were consistently directed to the exo face of the bicyclic framework with complete stereoselectivity. Preliminary biological testing of the adducts also showed positive anti-cancer activity, suggesting their potential pharmaceutical utility. Key words: 1,3-dipolar cycloaddition, nitrile oxide, oxabenzonorbornadiene, azabenzonorbornadiene, isoxazoline. Les reactions de cycloaddition dipolaire permette la synthese efficace d'heterocycles a cinq membres et offrent souvent differentes applications medicales. Nous avons etudie la cycloaddition 1,3-dipolaire des oxydes d'acetonitrile et de benzonitrile a des 7-oxabenzonorbornadienes et des 7-azabenzonorbornadienes, qui produit un assortiment d'isoxazolines fusionnees par l'entremise d'un heterobicycle, avec des rendements bons a excellents. Toutes les isoxazolines se sont systematiquement dirigees vers la face exo de la structure bicyclique montrant une stereoselectivite totale. Par ailleurs, des essais biologiques prealables des adduits ont mis en evidence une activite anti-cancereuse positive, ce qui indique leur possible utilite pharmaceutique. [Traduit par la Redaction] Mots-cles: cycloaddition 1,3-dipolaire, oxyde de nitrile, oxabenzonorbornadiene, azabenzonorbornadiene, isoxazoline., Introduction Cycloaddition reactions, for their powerful synthetic utility, have remained at the heart of annular framework construction over the years. (1) In particular, 1,3-dipolar cycloadditions have seen extensive use in [...]

Strain-promoted alkyne-nitrone cycloaddition (SPANC) reactions represent a bioorthogonal labeling strategy that is both very rapid and at the same time efficient and selective. Nitrones provide increased reaction rates as well as greater susceptibility toward stereoelectronic modification when compared with organic azides. We find that strain-promoted cycloadditions of cyclic nitrones with bicyclo[6.1.0]nonyne react with second-order rate constants as large as 1.49 L [mol.sup.-1] [s.sup.-1] at 25 °C. These reactions display rate constants that are up to 37-fold greater than those of the analogous reactions of benzyl azide with bicyclo[6.1.0]nonyne. We observed that reactions of nitrones with bicyclo[6.1.0]nonyne showed a stronger dependence on substituent effect for the reaction, as evidenced by a larger Hammett ρ value, than that for biaryl-aza-cyclooctanone. We demonstrate the ability to stereoelectronically tune the reactivity of nitrones towards different cyclooctynes in SPANC reactions. This ability to introduce selectivity into different SPANC reactions through substituent provides the opportunity to perform multiple SPANC reactions in one reaction vessel and opens up potential applications in multiplex labeling. Key words: metal-free bioothrogonal cycloadditions, 1,3-dipolar cycloadditions, nitrones, click chemistry, bicyclo[6.1.0]nonyne, strain-promoted alkyne-nitrone cycloaddition (SPANC). La reaction de cycloaddition par catalyse forcee de nitrones a un alcyne ('strain-promoted alkyne-nitrone cycloaddition 'ou SPANC) constitue une methode de marquage a la fois efficace, selective et tres rapide. Les nitrones augmentent les taux de reaction ameliore et la sensibilite aux modifications stereoelectroniques par comparaison avec les azotures organiques. Nous constatons que les reactions de cycloaddition par catalyse forcee de nitrones cycliques au bicyclo[6.1.0]nonyne ont lieu avec des taux de second ordre eleve de 1,49 L [mol.sup.-1] [s.sup.-1] a 25 °C. Ces reactions montrent des valeurs de taux jusqu'a 37 fois plus elevees que celles des reactions similaires de l'azoture de benzyle avec le bicyclo[6.1.0]nonyne. Nous avons observe que les reactions de nitrones avec le bicyclo[6.1.0]nonyne dependaient davantage de substituant sur la reaction, comme l'a montre l'augmentation de la valeur de Hammett ρ, que celles avec la biaryl-aza-cyclooctanone. Nous avons demontre qu'il etait possible d'ajuster stereoelectroniquement la reactivite des nitrones avec differents cyclooctynes dans des reactions de SPANC. Cette aptitude a introduire une selectivite dans differentes reactions de SPANC par l'intermediaires de substituants rend possible la realisation de multiples reactions de SPANC dans un reacteur unique et pourrait eventuellement etre appliquee au marquage multiple. [Traduit par la Redaction] Mots-cles : cycloadditions bioorthogonales sans metal, cycloadditions 1,3-dipolaires, nitrones, chimie 'click', bicyclo[6.1.0]nonyne, cycloaddition par catalyse forcee de nitrones a un alcyne (SPANC)., Introduction The study of complex biological systems at the molecular level requires the use of a powerful and highly selective nonperturbing probe or reporter reactions to produce coherent results with [...]

We, herein, report a novel--17 Da peptide modification corresponding to an N-terminal cyclization of peptides possessing the N-terminal motif of X-Asn-Gly. The cyclization occurs spontaneously during sample preparation for bottom-up proteomics studies. Distinct from the two well-known N-terminal cyclizations, cyclization of N-terminal glutamine and S-carbamoylmethylcysteine, it is dependent on pH instead of [N[H.sub.4.sup.+]]. The data set from our recent study on large-scale [N.sup.[alpha]]-modified peptides revealed a sequence requirement for the cyclization event similar to the well-known deamidation of Asn to isoAsp and Asp. Detailed analysis using synthetic peptides confirmed that the cyclization forms between the N-terminus and its neighboring Ash residue, and the reaction shares the same succinimide intermediate with the Asn deamidation event. As a result, we, here, propose a molecular mechanism for this specific cyclization. 10.1021/ac1019478

The RNA world hypothesis proposes that nucleic acids were once responsible for both information storage and chemical catalysis, before the advent of coded protein synthesis. However, it is difficult to imagine how nucleic acid polymers first appeared, as the abiotic chemical formation of long nucleic acid polymers from mononucleotides or short oligonucleotides remains elusive, and barriers to achieving this goal are substantial. One specific obstacle to abiotic nucleic acid polymerization is strand cyclization. Chemically activated short oligonucleotides cyclize efficiently, which severely impairs polymer growth. We show that intercalation, which stabilizes and rigidities nucleic acid duplexes, almost totally eliminates strand cyclization, allowing for chemical ligation of tetranucleotides into duplex polymers of up to 100 base pairs in length. In contrast, when these reactions are performed in the absence of intercalators, almost exclusively cyclic tetra- and octanucleotides are produced. Intercalator-free polymerization is not observed, even at tetranucleotide concentrations >10;000-fold greater than those at which intercalators enable polymerization. We also demonstrate that intercalation-mediated polymerization is most favored if the size of the intercalator matches that of the base pair; intercalators that bind to Watson--Crick base pairs promote the polymerization of oligonucleotides that form these base pairs. Additionally, we demonstrate that intercalation-mediated polymerization is possible with an alternative, non-Watson--Crick-paired duplex that selectively binds a complementary intercalator. These results support the hypothesis that intercalators (acting as 'molecular midwives') could have facilitated the polymerization of the first nucleic acids and possibly helped select the first base pairs, even if only trace amounts of suitable oligomers were available. base pair selection | origin of life | RNA world | polymerization | molecular evolution www.pnas.org/cgi/doi/10.1073/pnas.0914172107

The coupling of 2',3'-di-O-acetyl nicotinamide mononucleotide with 3-butyn-1-ol in the presence of 2,4,6- triisopropylbenzenesulfonyl chloride quantitatively afforded a terminal alcyne-containing intermediate. Furthermore, copper(I)-mediated Huisgen [3 + 2] cycloaddition with a series of azido compounds in a two-phase solvent system gave eight triazole-containing nicotinamide adenine dinucleotide analogs with yields over 88%. The cyclic voltammetric behaviors of these novel analogs were investigated with a glassy carbon electrode, and structural features of these analogs on their electrochemical properties were briefly discussed. Key words: nicotinamide adenine dinucleotide, analog, click chemistry, cyclic voltammetry. Le couplage du mononucleotide du 2',3'-di-O-acetylnicotinamide avec le but-3-yn-1-ol, en presence de chlorure de 2,4,6-triisopropylbenzenesulfonyle conduit a la formation pratiquement quantitative d'un intermediaire comportant un alcyne terminal. Une cycloaddition ulterieure [3 + 2] de Huisgen, catalysee par le cuivre(I), avec une serie de composes azide, dans un systeme liquide a deux phases, conduit a la formation, avec des rendements globaux superieurs a 88 %, d'analogues dinucleotides d'adenine nicotinamide contenant un triazole en position 8. On a etudie les comportements en voltamperometrie cyclique de ces nouveaux analogues a l'aide d'une electrode de carbone vitreux et on discute brievement des caracteristiques structurales de ces analogues sur leurs proprietes electrochimiques. Mots-cles : dinucleotide de l'adenine nicotinamide, analogue, chimie par clic, voltamperometrie cyclique. [Traduit par la Redaction], Introduction Nicotinamide adenine dinucleotide ([NAD.sup.+]) and its reduced form, NADH, are involved in numerous biological systems, especially as cofactors for enzymes mediating oxidoreductive reactions. (1) In those oxidoreductive reactions, NAD(H) [...]

Azide-terminated alkyl thiolate monolayer-protected gold nanoparticles (1-[C.sub.12]MPN) with a core size of 1.8 ± 0.2 nm were prepared. 1-[C.sub.12]MPN was modified in high yields via an uncatalyzed 1,3-dipolar cycloaddition (click-type reaction) with a variety of terminal acyl-alkynes under hyperbaric conditions at 11000 atm. The resulting 1,2,3- triazole modified MPNs (2-[C.sub.12]MPN) were characterized using ¹H NMR spectroscopy and were verified by comparison of the spectra to those obtained for the products of the model reactions of 1-azidododecane with the same alkynes. TEM analysis showed that the high-pressure conditions did not affect the size of the gold core, suggesting that the only effect is to facilitate the chemical reaction on the particles. Key words: nanoparticles, hyperbaric chemistry, 1,3-dipolar cycloaddition, monolayers. On a prepare des nanoparticules d'or protegees par une monocouche d'alkylthiol (1-[C.sub.12]MPN) portant une fonction azide en position terminale et dont le diametre principal est egal a 1,8 ± 0,2 nm. Le produit 1-[C.sub.12]MPN a ete modifie avec des rendements eleves par le biais d'une cycloaddition 1,3-dipolaire non catalysee (reaction de type par un clic) avec une variete d'acyl-alcynes terminales, dans des conditions hyperbariques, a 11,000 atmospheres. Les nanoparticules d'or modifiees, protegees par une monocouche d'alkylthiol (2-[C.sub.12]MPN) et portant un cycle 1,2,3-triazole ont ete caracterisees par spectroscopie RMN du 111 et ont ete verifiees par comparaison avec les spectres obtenus pour les produits des reaction' modeles du 1-azidodecane avec les memes alcynes. Une analyse par microscopie electronique a transmission (MET) a permis de montrer que les conditions de haute pression n'ont pas affecte la taille du diametre principal de l'or suggerant que le seul effet est de faciliter la reaction chimique sur les particules. Mots-cles : nanoparticules, chimie hyperbarique, cycloaddition 1, 3-dipolaire, monocouches. [Traduit par la Redaction], Introduction The Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition of azides to terminal alkynes to produce a triazole ring, the 'click' reaction, is a popular and powerful tool in organic synthesis and combinatorial [...]

Cyclic [beta]-1,2-glucans (C[beta]G) are periplasmic homopolysaccharides that have been shown to play an important role in several symbiotic and pathogenic relationships. Cyclic [beta]-1,2-glucan synthase (Cgs), the enzyme responsible for the synthesis of CLOG, is an integral membrane polyfunctional protein that catalyzes the four enzymatic activities (initiation, elongation, phosphorolysis, and cyclization) required for the synthesis of C[beta]G. Recently, we have identified the glycosyltransferase and the [beta]-1,2-glucooligosaccharide phosphorylase domains of Brucella abortus Cgs. In this study, we performed large-scale linker-scanning mutagenesis to gain further insight into the functional domains of Cgs. This analysis allowed us to construct a functional map of the enzyme and led to the identification of the minimal region required for the catalysis of initiation and elongation reactions. In addition, we identified the Cgs region (residues 991 to 1544) as being the protein domain required for cyclization and demonstrated that upon cyclization and releasing of the C[beta]G, one or more glucose residues remain attached to the protein intermediate that serves as a primer for the next round of C[beta]G synthesis. Finally, our results indicate that the overall control of the degree of polymerization of C[beta]G is the result of a balance between elongation, phosphorolysis, and cyclization reactions.

Abstract: This work deals with the molecular orbital calculation studies performed on different diazadienes to assess their reactivity pattern. The interaction of these diazadienes with various electron-poor and electron-rich dienophiles [...]

A highly enantioselective cyclization is developed through memory of chirality at ambient temperature, where powdered KOH in DMSO is shown to be an effective base. The studies have shown that enolates generated with powdered KOH in DMSO is extremely reactive.

Abstract: Isoxazole conjugates of sugar have been synthesized by the aid of 1,3-dipolar cycloaddition in a click chemistry approach. The sugar-derived propargyl ethers underwent 1,3-dipolar cycloadditions smoothly with in situ [...]

Abstract: The photochemistry of 1,1'-bi-2-naphthol (BINOL, 5) has been studied in aqueous solution and found to undergo rapid deuterium incorporation at the 4 and 5 positions (in D2O-CH3CN). All data [...]

An efficient route to prepare 4-(1',3'-dien-2'-yl)-2,5-dihydrofuran derivatives based on homodimeric coupling cyclization reaction of 2,3-allenols in presence of Pd[Cl.sub.2]/NaI as catalyst is reported.

Two protocols for the synthesis of 4-iodo-3-furanones through a sequence consisting of cyclization and 1,2-migration of 2-alkynyl-2-silyloxy carbonyl compounds are described.

The reactions involving the 5-hexenyl or the 6-heptenyl radical cyclization of a distant double bond at C4' and the radical center at C2' of the ribofuranose ring of thymidine are used for synthesizing North-type conformationally constrained cis-fused bicyclic five-membered and six-membered carbocyclic analogues of LNA and ENA. Enhanced lifetimes have made the carbocyclic-LNA and carbocyclic-ENA modifications very good candidates as potential antisense therapeutic agents.

A density functional theory based computational approach to describing the mechanistic course of the allene azide cycloaddition cascade sequence, which explains the different behaviors observed in the experimental studies between conjugated and nonconjugated species, is presented.

The stereochemistry of the aminopalladation step of various different catalyst systems of alkenes with two-faced reactivity is studied to analyze and report the cis- versus trans-aminopalladation in several aerobic Pd-catalyzed intramolecular Aza-Wacker reactions. The analysis reveals that the nitrogen nucleophile in such systems highly affect the aminopalladation pathway, hence leading to successful oxidative amination of alkenes.

The study explains and describes a concise, asymmetric and stereocontrolled total synthesis of stephacidins A, B and notamide B fungal metabolites, which act as extremely important functional groups for the formation of bridged bicyclic ring system. The synthesis technique makes use of the phenomenon of microwave heating, which shortens the reaction times and also increases the yield of the preparation of vital intermediates.

The study presents a mechanistic research and investigation of intramolecular aminoalkene and aminoalkyne hydroamination/cyclization that is normally catalyzed by several highly electrophilic and tetravalent constrained geometry complexes. The existence of identical reactivity trends, rate laws and activation parameters of the complexes prove the formation of an M-N [sigma]-bonded insertive pathway in the substance.

The reaction mechanism of the copper(II) carboxylate-promoted intramolecular carboamination of unactivated alkenes has provided a means to N-functionalized pyrrolidines and piperidines. The results have supported the mechanism wherein the N-C bond is formed through intramolecular syn aminocupration and the C-C bond is formed via intramolecular addition of a primary carbon radical to an aromatic ring.

The first stereoselective synthesis of (-)-(ent)-julifloridine, the antipode of naturally occurring alkaloid (+)-julifloridine, from L-alanine is reported. (-)-(ent)-Julifloridine is obtained from Sern oxidation of piperidine, followed by Wittig olefination and hydrogenation/debenzylation.

Controlled potential electrolysis (CPE) is used to investigate the electrochemical stability of isoxazolino[4,5:1,2][60]- and [70]fullerenes, which has undergone an efficient retro-cycloaddition reaction to pristine fullerene. The electrochemical retro-cycloaddition processes have shown that isoxazolinofullerenes are stable under oxidative conditions.

The first sequential one-pot double dearomatization of bis(N-benzyl-P,P-diphenylphosphinamides) is described via an anionic cyclization. The analysis provides a facile route of accessing the multifunctional systems with the antitumor properties, as the doubly phosphorylated systems prove to be active against a series of cancer line cells.

The reactivity and the intramolecular cyclizations of the bicyclic [delta]-hydroxynitriles are investigated. The analogues derived from such reactions after further reactions give various annulated enones, which is found to be a result of an initial elimination reaction to form alkenes, followed by the formation of the activated cyano group.

The synthesis and formation of the dimethyl gloiosiphone A, spiro[4,4]nonane skeleton is described by using the palladium-catalyzed domino cyclization of a linear 7-methylene-2,10-undecadienyl acetate. The one-pot two-step allylation is found to be a result of the oxidation of allylic ether moiety, in addition to the transformation of the vinyl group to an exo-methylene unit, giving the desired product.

The synthesis and the photovoltaic properties of a large number of efficient organic dyes, which consist of the benzo[b]furan moiety is studied. The analysis shows that the dyes are prepared by a one-pot coupling cyclization step, which makes it useful for various applications like the fabrication of a nanocrystalline Ti[O.sub.2] dye-sensitized solar cell.

A unique ECECCC electrochemical mechanism is employed for the electrosynthesis of a symmetric along with other similar monosubstituted derivatives. The predominance of the electrochemical oxidation versus the intramolecular cyclization technique is observed, which leads to the derivation of a variety of products with good yields.

The correlated effects of the folding/unfolding process and the formation of this N-terminal pyroglutamic acid are examined. The study results show that cyclization of N-terminal glutamine has no significant effect on the rate of either reductive unfolding or oxidative folding of the protein.

Catalytic and redox-active prosthetic groups are derived from post-translational modification of amino acid residues of proteins. These protein-derived cofactors typically rise from the oxygenation of aromatic residues, covalent cross-linking of amino acid residues or cleavage of internal amino acid residues.

Cinchona alkaloids under phase-transfer conditions were used to demonstrate the first organocatalytic enantioselective 1,6-addition of [beta]-ketoesters and benzophenone imine to electron-poor [delta]-unsubstituted dienes. The results reveal that the reaction, besides expanding the application of the principle of vinylogy in asymmetric catalytic synthesis gives an easy access to optically active [beta]-ketoesters and [alpha]-amino acid derivatives bearing a double bond and an electron-withdrawing group in the side chain.

A series of 2-substituted derivatives of saccharin are prepared by using the N-cumylsulfonamide directed metalation group (DMG), according to the directed ortho metalation (DoM) tactic. It is seen that mild conditions for N-decumylation and other simple transformations of the products are achieved, 4,7- disubstituted saccharins are obtained and mild TFA-mediated N-decumylation yields substituted primary arylsulfonamides.

The feasibility of ruthenium-catalyzed cyclization of 2-alkyl-1-ethynylbenzenes through benzene 1,5-hydrogen shift activated by a cationic ruthenium-vinylidine intermediate is studied. It is found that catalytic cyclization of 2-alkyl-1-ethynylbenzene derivatives has formed 1-substituted-1H-indene products.

Several approaches that include photoinduced electron transfer are employed to functionalize the single-walled carbon nanotubes, which are normally accompanied by covalently linked phthalocyanine addends. The process also exhibits various phenomenons, like charge-separation and charge-recombination that shows that the radical ion pair product in dimethylformadide is highly stabilized.

The nature of 6[pi] electrocyclizations of four different dienylketenes (2-furanly, 2-pyrrolyl, cyclopenta-1,3-dienyl, and 2-thiophenyl-substituted ketenes) to corresponding cyclo hexadienones is studied. The results indicate a pericyclic character of the processes for the dienylketenes despite the relatively small nucleus-independent chemical shifts, (NICS) values in the transition states.

The two-step synthesis of the new 12- and 13-membered benzodioxotetraaza macrocycles is described and the protonation components of both ligands are determined by [super 1]H NMR titration and by potentiometry. The in vitro stability is analyzed in the presence of different buffers or with an excess of diethylenetriamine-pentaethanoic acid, indicating that the incubation of the radiocopper complex in human serum showed 6% protein binding.

Topographical analysis of the molecular electrostatic potential (MESP) along a reaction path is used to bring out the sequential electronic reorganizations for 1,3-dipolar cycloadditions of ethyne to fulminic acid as well as diazomethane. The MESP topography at each point on the reaction path is associated with classical electronic structure, thereby providing a clear picture of the electronic reorganization along the reaction path.

A study explores the tuning of the Bergman cyclization by analyzing the rearrangement of two osmaenediynes and one rhodaenediyne by the introduction of metal fragments at its various positions. The activation energy of the rearrangement of the rhodaenediyne is found to be the same as that of the parent enediyne, hence making the study of the diradical nature of the resulting intermediates possible.

An in situ, two-step protodeamination route is employed for the synthesis of a series of constrained geometry organoactinides, which are generally used as catalysts for the intramolecular hydroamination or cyclization of primary and secondary amines with diverse tethered C-C unsaturation. The complexes thus formed are found to exhibit large turnover frequencies, as well as high regioselectivities throughout the experiment.

The sequential rhodium-catalyzed silycarbocyclization followed by palladium-catalyzed cross-coupling reactions is described to synthesize functionalized cyclopentanes with a highly substituted exocyclic double bond. The reaction that involved 1,6-enynes and underwent silylcarbocyclization, found that if the enyne bears an electron-deficient double bond then the major side reaction, silyformation, can be suppressed by carrying out reaction under a substochiometric amount of CO.

A short, two-step approach based on a Ugi multicomponent reaction (MCR) followed by a subsequent intramolecular [S.sub.N]2 reaction is described for the synthesis of diazepane or diazocane systems. The results have shown the power of coupling Ugi MCRs with post-condensation transformations for obtaining relatively complex heterocyclic scaffolds in few steps.

An efficient total synthesis of antibiotic (-)-codonopsinine is achieved from D-alanine as a chiral template. The vital steps of the method are modified Sharpless asymmetric dihydroxylation reaction and the highly stereoselective intramolecular acid-catalyzed amidocyclization.

A cationic rhodium(I)/Segphos complex has catalyzed an enantio- and diastereoselective intermolecular [2+2+2] cycloaddition of 1,2-bis(arylpropiolyl)benzenes with various monoalkynes in order to produce axially chiral 1,4-teraryls possessing an anthraquinone structure. A thermal intramolecular [4+2] cycloaddition of 1,2-bis(arylpropiolyl)benzenes has proceeded at 60 [degree]C to produce aryl-substituted naphthacenediones in moderate to good yields.

Indazolium-3-amidates have undergone [3+2]-cycloadditions with activated triple bonds to spiro[indazole-3,3'-pyrroles]. Heternuclear single quantum coherence (HSQC), heteronuclear multiple bond correlation (HMBC), nuclear Overhauser enhancement spectroscopy (NOESY) and [super 1]H/[super 15]N correlations are used to examined the structures of the cycloadducts.

The thermal [C.sup.2]-[C.sup.6] cyclization of the enyne-allenes and their ring-closed and ring-opened products is described using an ultrafast radical clock. The results have provided a direct evidence for a stepwise mechanism in the [C.sup.2]-[C.sup.6] cyclization of enyne-allenes.

The complex bioactive natural and unnatural benzopyran congeners were synthesized using one/two-step approaches. The congeners were synthesized by phenol directed intramolecular diastereoselective dipolar thermal/base catalyzed [2+] cycloaddition approach.

A method for three different types of carbocyclic frameworks belonging to dupreziananes, sterpuranes and polyquinanes is described. The process involves ring-closing metathesis on appropriately designed bicyclo[2.2.2]octenones and photochemical transformations of the resulting tricyclic systems.

A general synthetic method fro pyrroquinolizidines (3,4,5,5a,6,7,8-heptahydropyrrolo[2,1,5-de]-quinozilines) by munchnone 1,3-dipolar cycloaddition is described. This method was used in the synthesis of an unnatural pyrroloqunilizidine homologue of myrmicarin 215B.

Abstract: A [C.sub.60]-based ebselen derivative 4 was synthesized through the cycloaddition of [C.sub.60 with the azide (3) containing the ebselen component. It was obtained in a four-step synthesis starting from [...]