Showing papers in "Journal of Organic Chemistry in 2008"
TL;DR: While the electrophilicity of the molecules accounts for the reactivity toward nucleophiles, it is shown that a simple index chosen for the nucleophilicity, Nu, based on the HOMO energy is useful explaining the reactsivity of these CD ethylenes toward electrophiles.
Abstract: The electrophilic/nucleophilic character of a series of captodative (CD) ethylenes involved in polar cycloaddition reactions has been studied using DFT methods at the B3LYP/6-31G(d) level of theory. The transition state structures for the electrophilic/nucleophilic interactions of two CD ethylenes toward a nucleophilically activated ethylene, 2-methylene-1,3-dioxolane, and an electrophilically activated ethylene, 1,1-dicyanoethyelene, have been studied, and their electronic structures have been characterized using both NBO and ELF methods. Analysis of the reactivity indexes of the CD ethylenes explains the reactivity of these species. While the electrophilicity of the molecules accounts for the reactivity toward nucleophiles, it is shown that a simple index chosen for the nucleophilicity, Ν, based on the HOMO energy is useful explaining the reactivity of these CD ethylenes toward electrophiles.
795 citations
TL;DR: A critical reevaluation of all four reactions has provided no evidence for the existence of nonthermal microwave effects, and the observed effects were purely thermal and not related to the microwave field.
Abstract: The concept of nonthermal microwave effects has received considerable attention in recent years and is the subject of intense debate in the scientific community. Nonthermal microwave effects have been postulated to result from a direct stabilizing interaction of the electric field with specific (polar) molecules in the reaction medium that is not related to a macroscopic temperature effect. In order to probe the existence of nonthermal microwave effects, four synthetic transformations (Diels-Alder cycloaddition, alkylation of triphenylphosphine and 1,2,4-triazole, direct amide bond formation) were reevaluated under both microwave dielectric heating and conventional thermal heating. In all four cases, previous studies have claimed the existence of nonthermal microwave effects in these reactions. Experimentally, significant differences in conversion and/or product distribution comparing the conventionally and microwave-heated experiments performed at the same measured reaction temperature were found. The current reevaluation of these reactions was performed in a dedicated reactor setup that allowed accurate internal reaction temperature measurements using a multiple fiber-optic probe system. Using this technology, the importance of efficient stirring and internal temperature measurement in microwave-heated reactions was made evident. Inefficient agitation leads to temperature gradients within the reaction mixture due to field inhomogeneities in the microwave cavity. Using external infrared temperature sensors in some cases results in significant inaccuracies in the temperature measurement. Applying the fiber-optic probe temperature monitoring device, a critical reevaluation of all four reactions has provided no evidence for the existence of nonthermal microwave effects. Ensuring efficient agitation of the reaction mixture via magnetic stirring, no significant differences in terms of conversion and selectivity between experiments performed under microwave or oil bath conditions at the same internally measured reaction temperatures were experienced. The observed effects were purely thermal and not related to the microwave field.
483 citations
TL;DR: The synthesis and photophysical/electrochemical properties of a series of novel starburst triarylamine-based organic dyes as well as their application in dye-sensitized nanocrystalline TiO2 solar cells (DSSCs) suggest that the dyes based on starburst triphenylamine donor are promising candidates for improvement of the performance of the DSSCs.
Abstract: We report here on the synthesis and photophysical/electrochemical properties of a series of novel starburst triarylamine-based organic dyes (S1, S2, S3, and S4) as well as their application in dye-sensitized nanocrystalline TiO2 solar cells (DSSCs). For the four designed dyes, the starburst triarylamine group and the cyanoacetic acid take the role of electron donor and electron acceptor, respectively. It was found that the introduction of starburst triarylamine group to form the D-D-pi-A configuration brought about superior performance over the simple D-pi-A configuration, in terms of bathochromically extended absorption spectra, enhanced molar extinction coefficients and better thermo-stability. Moreover, the HOMO and LUMO energy levels tuning can be conveniently accomplished by alternating the donor moiety, which was confirmed by electrochemical measurements and theoretical calculations. The DSSCs based on the dye S4 showed the best photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 85%, a short-circuit photocurrent density (J(sc)) of 13.8 mA cm(-2), an open-circuit photovoltage (V(oc)) of 0.63 V, and a fill factor (ff) of 0.69, corresponding to an overall conversion efficiency of 6.02% under 100 mW cm(-2) irradiation. This work suggests that the dyes based on starburst triphenylamine donor are promising candidates for improvement of the performance of the DSSCs.
415 citations
TL;DR: A new, convenient method for the syntheses of 2-substituted benzimidazole and benzothizole is described, with short reaction times, large-scale synthesis, easy and quick isolation of the products, excellent chemoselectivity, and excellent yields.
Abstract: A new, convenient method for the syntheses of 2-substituted benzimidazole and benzothizole is described. Short reaction times, large-scale synthesis, easy and quick isolation of the products, excellent chemoselectivity, and excellent yields are the main advantages of this procedure.
387 citations
TL;DR: The use of pivalic acid as the reaction solvent, instead of acetic acid, results in greater reproducibility, higher yields, and broader scope, and the use of electron-rich diarylamines as illustrated in the synthesis of three naturally occurring carbazole products.
Abstract: New reaction conditions for intramolecular palladium(II)-catalyzed oxidative carbon-carbon bond formation under air are described. The use of pivalic acid as the reaction solvent, instead of acetic acid, results in greater reproducibility, higher yields, and broader scope. This includes the use of electron-rich diarylamines as illustrated in the synthesis of three naturally occurring carbazole products: Murrayafoline A, Mukonine, and Clausenine. A variety of side products have also been isolated, casting light on competing reaction pathways and revealing new reactivity with palladium(II) catalysis.
329 citations
TL;DR: Thermal stability of CO2 adducts of N-heterocyclic carbenes (NHCs) was studied by means of in situ FTIR method with monitoring of the nu(CO2) region of the infrared spectra under various conditions, and the relatively unstable IPr-CO2 exhibits the highest catalytic activity.
Abstract: Thermal stability of CO2 adducts of N-heterocyclic carbenes (NHCs) was studied by means of in situ FTIR method with monitoring of the nu(CO2) region of the infrared spectra under various conditions. 1,3-Bis(2,6-diisopropylphenyl)imidazolinium-2-carboxylate (SIPr-CO2) shows higher thermal stability compared with 1,3-bis(2,6-diisopropylphenyl)imidazolium-2-carboxylate (IPr-CO2). The presence of free CO2 can significantly inhibit the decomposition of NHC-CO2 adducts, while the addition of an epoxide such as propylene oxide has a negative effect on stabilizing these adducts. As zwitterionic compounds, NHC-CO2 adducts were also proved to be effective organic catalysts for the coupling reaction of CO2 and epoxides to afford cyclic carbonates, for which a possible mechanism was proposed. Among these NHC-CO2 adducts, the relatively unstable IPr-CO2 exhibits the highest catalytic activity. The presence of an electrophile such as SalenAlEt could greatly improve the catalytic activity of IPr-CO2 due to intermolecular cooperative catalysis of the binary components.
310 citations
TL;DR: The synthesis and evaluation of a novel calix[4]arene-based fluorescent chemosensor 8 for the detection of Cd(2+) and Zn(2+) and the fluorescent spectra changes observed upon addition of various metal ions show that 8 is highly selective for Cd (2+)
Abstract: The synthesis and evaluation of a novel calix[4]arene-based fluorescent chemosensor 8 for the detection of Cd(2+) and Zn(2+) is described. The fluorescent spectra changes observed upon addition of various metal ions show that 8 is highly selective for Cd(2+) and Zn(2+) over other metal ions. Addition of Cd(2+) and Zn(2+) to the solution of 8 results in ratiometric measurement.
293 citations
TL;DR: By analyzing the scaffold content of the CAS Registry, this work believes this power law is evidence that the minimization of synthetic cost has been a key factor in shaping the known universe of organic chemistry.
Abstract: By analyzing the scaffold content of the CAS Registry, we attempt to characterize in a comprehensive way the structural diversity of organic chemistry. The scaffold of a molecule is taken to be its framework, defined as all its ring systems and all the linkers that connect them. Framework data from more than 24 million organic compounds is analyzed. The distribution of frameworks among compounds is found to be top-heavy, i.e., a small percentage of frameworks occur in a large percentage of compounds. When frameworks are analyzed at the graph level, an even more top-heavy distribution is found: half of the compounds can be described by only 143 framework shapes. The most significant finding is that the framework distribution conforms almost exactly to a power law. This suggests that the more often a framework has been used as the basis for a compound, the more likely it is to be used in another compound. This may be explained by the cost of synthesis: making a new derivative of a framework is probably less...
263 citations
TL;DR: A rhodamine-cyclen conjugate behaves as a highly sensitive and selective fluorescent chemosensor for Hg(2+)(2+) due to the formation of 1-Hg( 2+) 1:2 complex leading to spirocycle opening of 1.
Abstract: A rhodamine−cyclen conjugate (1) behaves as a highly sensitive and selective fluorescent chemosensor for Hg2+. The high emission selectivity is due to the formation of 1−Hg2+ 1:2 complex leading to spirocycle opening of 1.
252 citations
TL;DR: A method for the Pd-catalyzed carbonylation of aryl bromides has been developed using Xantphos as the ligand and an X-ray crystal structure was obtained revealing an unusual cis-coordination mode of Xanphos in this palladium-acyl complex.
Abstract: A method for the Pd-catalyzed carbonylation of aryl bromides has been developed using Xantphos as the ligand. This method is effective for the direct synthesis of Weinreb amides, 1° and 2° benzamides, and methyl esters from the corresponding aryl bromides at atmospheric pressure. In addition, a putative catalytic intermediate, (Xanphos)Pd(Br)benzoyl, was prepared and an X-ray crystal structure was obtained revealing an unusual cis-coordination mode of Xantphos in this palladium−acyl complex.
251 citations
TL;DR: The development of a new method for the assembly of unsymmetrical carbazole product can be controlled by the design of the biaryl amide substrate, and the method is compatible with a variety of functional groups.
Abstract: The development of a new method for the assembly of unsymmetrical carbazoles is reported. The strategy involves the selective intramolecular functionalization of an arene C-H bond and the formation of a new arene C-N bond. The substitution pattern of the carbazole product can be controlled by the design of the biaryl amide substrate, and the method is compatible with a variety of functional groups. The utility of the new protocol was demonstrated by the concise synthesis of three natural products from commercially available materials.
TL;DR: Two copper-catalyzed approaches complement existing strategies for benzoxazole synthesis, which typically utilize 2-aminopheonls as precursors, and an alternative more versatile one-pot domino annulation strategy was developed.
Abstract: Two domino annulation approaches for benzoxazole synthesis have been developed. In the first approach, copper-catalyzed intermolecular cross-coupling of 1,2-dihaloarenes with primary amides initially forms the Ar−N bond of the benzoxazole ring, followed by copper-catalyzed intramolecular cyclization to form the Ar−O bond. Benzoxazoles were formed in good yields for the reaction of 1,2-dibromobenzene, but the reaction was not regioselective for the reaction of 3,4-dibromotoluene. Furthermore, the method is limited by the availability of 1,2-dihaloarenes. As a result of these limitations, an alternative more versatile one-pot domino annulation strategy was developed involving reaction of 2-bromoanilines with acyl chlorides in the presence of Cs2CO3, catalytic CuI, and the non-acylatable ligand 1,10-phenanthroline. Under these conditions initial acylation of the aniline is followed by copper-catalyzed intramolecular cyclization of the resultant 2-haloanilide to form the Ar−O bond of the benzoxazole ring. Opt...
TL;DR: The newly developed adaptive natural density partitioning method has been applied to a series of organic aromatic mono- and polycyclic molecules, including cyclopropenyl cation, cyclopentadienyl anion, benzene, naphthalene, anthracene, phenanthrene, triphenylene, and coronene, leading to unique, compact, graphic formulas.
Abstract: The newly developed adaptive natural density partitioning (AdNDP) method has been applied to a series of organic aromatic mono- and polycyclic molecules, including cyclopropenyl cation, cyclopentadienyl anion, benzene, naphthalene, anthracene, phenanthrene, triphenylene, and coronene. The patterns of chemical bonding obtained by AdNDP are consistent with chemical intuition and lead to unique, compact, graphic formulas. The resulting bonding patterns avoid resonant description and are always consistent with the point symmetry of the molecule. The AdNDP representation of aromatic systems seamlessly incorporates localized and delocalized bonding elements.
TL;DR: Spectral data for these materials indicate they are highly fluorescent probes in aqueous environments.
Abstract: The objective of this work was to form water-soluble 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives. Sulfonation conditions were developed for several BODIPY dyes to give the monosulfonated products 1a−3a and the disulfonated products 1b−3b. Compounds 1 are functionalized with an aryl iodide for organometallic couplings. Similarly, 2 has an aromatic bromide but also two chlorine atoms that could be replaced via SNAr reactions. The amine 3 is amenable to couple to biomolecules via acylation reactions. A diazotization/azide reaction sequence was used to convert the amines 3 into azides 4; the latter may be functionalized via click reactions as illustrated by conversion of 4b into 5. Compound 5 was designed to have an acid-functional group to facilitate activation and coupling to amines. Spectral data for these materials indicate they are highly fluorescent probes in aqueous environments.
TL;DR: A protocol for the copper-catalyzed aryl-sulfur bond formation between aryL iodides and thiophenols is reported and a variety of diaryl thioethers are synthesized under relatively mild reaction conditions with good chemoselectivity and functional group tolerance.
Abstract: A protocol for the copper-catalyzed aryl-sulfur bond formation between aryl iodides and thiophenols is reported. The reaction is catalyzed by a low amount (1-2.5 mol %) of readily available and ligand-free copper iodide salt. A variety of diaryl thioethers are synthesized under relatively mild reaction conditions with good chemoselectivity and functional group tolerance.
TL;DR: The use of 3,4,7,8-tetramethyl-1,10-phenanthroline (Me(4)Phen) as a ligand improves the Cu-catalyzed cross-coupling reactions of aryl iodides and bromides with primary and secondary aliphatic, benzylic, allylic, and propargylic alcohols.
Abstract: The use of 3,4,7,8-tetramethyl-1,10-phenanthroline (Me4Phen) as a ligand improves the Cu-catalyzed cross-coupling reactions of aryl iodides and bromides with primary and secondary aliphatic, benzylic, allylic, and propargylic alcohols. Most importantly, by employing this catalyst system, the need to use an excessive quantity of the alcohol coupling partner is alleviated. The relatively mild conditions, short reaction times, and moderately low catalyst loading allow for a wide array of functional groups to be tolerated on both the electrophilic and nucleophilic coupling partners.
TL;DR: In addition to electron-rich arenes and heteroarenes, allylsilanes and 1,3-dicarbonyl compounds can be used as the nucleophiles and the 5-endo-dig pathway is preferred in the reaction of 1,5-enynes with carbon nucleophile.
Abstract: Gold(I)-catalyzed addition of carbon nucleophiles to 1,6-enynes gives two different type of products by reaction at the cyclopropane or at the carbene carbons of the intermediate cyclopropyl gold carbenes. The 5-exo-dig cyclization is followed by most 1,6-enynes, although those bearing internal alkynes and alkenes react by the 6-endo-dig pathway. The cyclopropane versus carbene site-selectivity can be controlled in some cases by the ligand on the gold catalyst. In addition to electron-rich arenes and heteroarenes, allylsilanes and 1,3-dicarbonyl compounds can be used as the nucleophiles. In the reaction of 1,5-enynes with carbon nucleophiles, the 5-endo-dig pathway is preferred.
TL;DR: The results with hexopyranosides suggest that biologically relevant cell-surface oligosaccharides could be targeted in water using oligomeric benzoboroxole receptors.
Abstract: In contrast to normal boronic acids, o-hydroxymethyl phenylboronic acid (benzoboroxole) has the capability of complexing glycopyranosides efficiently in neutral water. The measurement of association constants with a panel of model hexopyranosides indicates that the preferred mode of binding is through a cis-3,4-diol, such as that found in galactopyranosides, and mass spectrometric studies support a 1:1 binding stoichiometry. The complexation of glucopyranosides is weaker, and they are bound through their 4,6-diol unit. Although several factors may explain the exceptional carbohydrate-binding behavior of this class of hemiboronic acids, the relatively high Lewis acidity of benzoboroxoles is a likely contributing factor along with subtle factors such as intramolecular hydrogen bonds with other hydroxyl groups in the resulting anionic complex. These results with hexopyranosides suggest that biologically relevant cell-surface oligosaccharides could be targeted in water using oligomeric benzoboroxole receptors.
TL;DR: A novel fluorescent probe that possess both BODIPY and Rhodamine moieties has been designed for the selective detection of Hg( 2+) and Ba(2+) ions on the controlling by a logic gate and the concept has been used to construct a combinational logic circuit at the molecular level.
Abstract: A novel fluorescent probe that possess both BODIPY and Rhodamine moieties has been designed for the selective detection of Hg2+ and Ba2+ ions on the controlling by a logic gate. The characteristic fluorescence of the Ba2+-selective OFF−ON and the Hg2+-selective fluorescence bathochromic shift can be observed, and the concept has been used to construct a combinational logic circuit at the molecular level. These results will be useful for further molecular design to mimic the function of the complex logic gates on controlling.
TL;DR: This paper describes a regiospecific, sequential one-pot synthesis of symmetrical and unsymmetrical diaryliodonium tetrafluoroborates, which are the most popular salts in metal-catalyzed arylations.
Abstract: Diaryliodonium salts have recently received considerable attention as mild arylation reagents in organic synthesis. This paper describes a regiospecific, sequential one-pot synthesis of symmetrical and unsymmetrical diaryliodonium tetrafluoroborates, which are the most popular salts in metal-catalyzed arylations. The protocol is fast and high-yielding and has a large substrate scope. Furthermore, the corresponding diaryliodonium triflates can conveniently be obtained via an in situ anion exchange.
TL;DR: A DFT analysis of the global electrophilicity and nucleophilicity of the reagents provides a sound explanation about the participation of 1 as a nucleophile in these cycloadditions.
Abstract: The formal [2σ + 2σ + 2π] cycloaddition of quadricyclane, 1, with dimethyl azodicarboxylate, 2, in water has been studied using DFT methods at the B3LYP/6−31G** and MPWB1K/6−31G** levels. In the gas phase, the reaction of 1 with 2 has a two-stage mechanism with a large polar character and an activation barrier of 23.2 kcal/mol. Inclusion of water through a combined discrete-continuum model changes the mechanism to a two-step model where the first nucleophilic attack of 1 to 2 is the rate-limiting step with an activation barrier of 14.7 kcal/mol. Analysis of the electronic structure of the transition state structures points out the large zwitterionic character of these species. A DFT analysis of the global electrophilicity and nucleophilicity of the reagents provides a sound explanation about the participation of 1 as a nucleophile in these cycloadditions. This behavior is reinforced by a further study of the reaction of 1 with 1,1-dicyanoethylene.
TL;DR: It was proposed that hot water acted as a modest acid catalyst, reactant, and solvent in the hydrolysis reactions of epoxides and aziridines in hot water.
Abstract: Effective hydrolysis of epoxides and aziridines was conducted by heating them in water at 60 or 100 °C. Other types of nucleophile such as amines, sodium azide, and thiophenol could also efficiently open epoxides and aziridines in hot water. It was proposed that hot water acted as a modest acid catalyst, reactant, and solvent in the hydrolysis reactions.
TL;DR: The proposal that bimolecular cycloaddition reactions take place initially between triple bonds and sulfonyl azides to give N-sulfonyl triazolyl copper intermediates was verified by a trapping experiment and the proposed mechanistic framework is in good agreement with the obtained kinetics and competition studies.
Abstract: Combined analyses of experimental and computational studies on the Cu-catalyzed three-component reactions of sulfonyl azides, terminal alkynes and amines, alcohols, or water are described. A range of experimental data including product distribution ratio and trapping of key intermediates support the validity of a common pathway in the reaction of 1-alkynes and two distinct types of azides substituted with sulfonyl and aryl(alkyl) groups. The proposal that bimolecular cycloaddition reactions take place initially between triple bonds and sulfonyl azides to give N-sulfonyl triazolyl copper intermediates was verified by a trapping experiment. The main reason for the different outcome from reactions between sulfonyl and aryl(alkyl) azides is attributed to the lability of the N-sulfonyl triazolyl copper intermediates. These species are readily rearranged to another key intermediate, ketenimine, into which various nucleophiles such as amines, alcohols, or water add to afford the three-component coupled products: amidines, imidates, or amides, respectively. In addition, the proposed mechanistic framework is in good agreement with the obtained kinetics and competition studies. A computational study (B3LYP/LACV3P*+) was also performed confirming the proposed mechanistic pathway that the triazolyl copper intermediate plays as a branching point to dictate the product distribution.
TL;DR: The employment of Cu(I)-catalyzed 1,3-dipolar cycloaddition of side chains modified with azido and alkynyl functions is reported and alternative synthetic routes to efficiently generate 1,4-disubstituted [1,2,3]triazolyl-containing cyclopeptides are explored.
Abstract: Intramolecular side-chain to side-chain cyclization is an established approach to achieve stabilization of specific conformations and a recognized strategy to improve resistance toward proteolytic degradation. To this end, cyclizations, which are bioisosteric to the lactam-type side-chain to side-chain modification and do not require orthogonal protection schemes, are of great interest. Herein, we report the employment of Cu(I)-catalyzed 1,3-dipolar cycloaddition of side chains modified with azido and alkynyl functions and explore alternative synthetic routes to efficiently generate 1,4-disubstituted [1,2,3]triazolyl-containing cyclopeptides. The solid-phase assembly of the linear precursor including epsilon-azido norleucine and the propargylglycine (Pra) in positions i and i+4, respectively, was accomplished by either subjecting the resin-bound peptide to selective on-resin diazo transformation of a Lys into the Nle(epsilon-N3) or the incorporation of Fmoc-Nle(epsilon-N3)-OH during the stepwise build-up of the resin-bound peptide 1b. Solution-phase Cu(I)-catalyzed 1,3-dipolar cycloaddition converts the linear precursor Ac-Lys-Gly-Nle(epsilon-N3)-Ser-Ile-Gln-Pra-Leu-Arg-NH2 (2) into the 1,4-disubstituted [1,2,3]triazolyl-containing cyclopeptide [Ac-Lys-Gly-Xaa(&(1))-Ser-Ile-Gln-Yaa(&(2))-Leu-Arg-NH2][(&(1)(CH2)4-1,4-[1,2,3]triazolyl-CH2&(2))] (3). The conformational preferences of the model cyclopeptide 3 (III), which is derived from the sequence of a highly helical and potent i to i+4 side-chain to side-chain lactam-containing antagonist of parathyroid hormone-related peptide (PTHrP), are compared to the corresponding lactam analogue Ac[Lys(13)(&(1)),Asp(17)(&(2))]hPTHrP(11-19)NH2 (II). CD and NMR studies of 3 and II in water/hexafluoroacetone (HFA) (50:50, v/v) revealed a high prevalence of turn-helical structures involving in particular the cyclic regions of the molecule. Despite a slight difference of the backbone arrangement, the side-chains of Ser, Gln, and Ile located at the i+1 to i+3 of the ring-forming sequences share the same spatial orientation. Both cyclopeptides differ regarding the location of the turn-helical segment, which in II involves noncyclized residues while in 3 it overlaps with residues involved in the cyclic structure. Therefore, the synthetic accessibility and conformational similarity of i to i+4 side-chain to side-chain cyclopeptide containing the 1,4-disubstituted [1,2,3]triazolyl moiety to the lactam-type one may result in similar bioactivities.
TL;DR: A highly chemoselective reduction of aromatic nitro compounds to the corresponding amino derivatives has been achieved by a combination of copper nanoparticles and ammonium formate in ethylene glycol at 120 degrees C.
Abstract: A highly chemoselective reduction of aromatic nitro compounds to the corresponding amino derivatives has been achieved by a combination of copper nanoparticles and ammonium formate in ethylene glycol at 120 °C. The reductions are successfully carried out in presence of a wide variety of other reducible functional groups in the molecule, such as Cl, I, OCH2Ph, NHCH2Ph, COR, COOR, CN, etc. The reactions are very clean and high yielding.
TL;DR: This Perspective describes how chemists can control intermolecular [2 + 2] photodimerizations in the solid state using small molecules as linear templates using hydrogen bond donor and acceptor groups of the templates.
Abstract: This Perspective describes how chemists can control intermolecular [2 + 2] photodimerizations in the solid state using small molecules as linear templates. The templates assemble olefins into positions for the reaction via hydrogen-bond-driven self-assembly. We attach functional groups to the olefins that complement hydrogen bond donor and acceptor groups of the templates. The resulting cyclobutane-based products form stereospecifically, quantitatively, and in gram amounts. The templates are used to direct the formation of a [2.2]paracyclophane and ladderanes. The organic solid state is an exciting medium within which to control chemical reactivity since it is possible to synthesize, or construct, molecules that may be, otherwise, unobtainable from solution. The products form with a high degree of stereocontrol provided by a crystal lattice. The critical covalent-bond-forming process also occurs in a solvent-free environment. That molecules are virtually frozen in position in a solid also means that this ...
TL;DR: The amide group in anilides was found to functionalize as an elegant directing group to convert aromatic sp(2) C-H bonds into C-O bonds in high regioselectivity with acetic acid as the acetate source and K( 2)S(2,O(8)O( 8) as the oxidant.
Abstract: Various anilides have been directly ortho-acetoxylated through a Pd(OAc)2-catalyzed C−H bond activation process. The amide group in anilides was found to functionalize as an elegant directing group to convert aromatic sp2 C−H bonds into C−O bonds in high regioselectivity with acetic acid as the acetate source and K2S2O8 as the oxidant.
TL;DR: This indium catalytic system successfully accommodated the intramolecular cyclization of other arylalkyne skeletons involving a carboxylic acid and an amide group.
Abstract: Use of a 2-ethynylaniline having an alkyl or aryl group on the terminal alkyne selectively produced a variety of polyfunctionalized indole derivatives in moderate to excellent yields via indium-catalyzed intramolecular cyclization of the corresponding alkynylaniline. In contrast, employment of a substrate with a trimethylsilyl group or with no substituent group on the terminal triple bond, exclusively afforded polysubstituted quinoline derivatives in good yields via indium-promoted intermolecular dimerization of the ethynylaniline. This indium catalytic system successfully accommodated the intramolecular cyclization of other arylalkyne skeletons involving a carboxylic acid and an amide group.
TL;DR: A clear picture emerges: nucleophilicity is determined by the electron-donor capability of the nucleophile (i.e., energy and shape of the X(-) np atomic orbital), and leaving-group ability derives directly from carbon-leaving group (C-Y) bond strength.
Abstract: Nucleophilic substitution is ubiquitous in chemistry and well studied. Nucleophilicity and leaving-group ability have been related to various reactant properties, such as electronegativity, size, polarizability, and others. Yet, the state-of-the-art is to some extent still phenomenological. Here, we try to arrive at a straightforward, causal relationship between the reactants’ electronic structure and their SN2 reactivity. To this end, we have explored the potential energy surfaces of the backside as well as frontside SN2 reactions of X− + CH3Y with X, Y = F, Cl, Br, and I, using relativistic density functional theory (DFT) at ZORA-OLYP/TZ2P. These explorations provide us with a consistent overview of trends, over a wide range of reactivities and pathways, which were analyzed using the activation strain model of chemical reactivity. A clear picture emerges from these analyses: nucleophilicity is determined by the electron-donor capability of the nucleophile (i.e., energy and shape of the X− np atomic orbi...
TL;DR: The use of fluorinated alcohols such as 2,2,2-trifluoroethanol (TFE) and 1,1,3,3-hexafluoro-2-propanol (HFIP) as solvents dramatically increases the regioselectivity in the pyrazole formation, and this modification is used in a straightforward synthesis of fluorination analogs of Tebufenpyrad with acaricide activity.
Abstract: The preparation of N-methylpyrazoles is usually accomplished through reaction of a suitable 1,3-diketone with methylhydrazine in ethanol as the solvent. This strategy, however, leads to the formation of regioisomeric mixtures of N-methylpyrazoles, which sometimes are difficult to separate. We have determined that the use of fluorinated alcohols such as 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as solvents dramatically increases the regioselectivity in the pyrazole formation, and we have used this modification in a straightforward synthesis of fluorinated analogs of Tebufenpyrad with acaricide activity.