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Showing papers in "Journal of Organic Chemistry in 2007"


Journal ArticleDOI
TL;DR: Results show that energetic tuning of the chromophores was successful and fulfilled the thermodynamic criteria for dye-sensitized solar cells, electrical losses depending on the size and orientation of the Chromophores were observed.
Abstract: A series of organic chromophores have been synthesized in order to approach optimal energy level composition in the TiO2−dye−iodide/triiodide system in the dye-sensitized solar cells. HOMO and LUMO energy level tuning is achieved by varying the conjugation between the triphenylamine donor and the cyanoacetic acid acceptor. This is supported by spectral and electrochemical experiments and TDDFT calculations. These results show that energetic tuning of the chromophores was successful and fulfilled the thermodynamic criteria for dye-sensitized solar cells, electrical losses depending on the size and orientation of the chromophores were observed.

572 citations


Journal ArticleDOI
TL;DR: The oxidative coupling of benzoic acids with internal alkynes effectively proceeds in the presence of [Cp*RhCl2]2 and Cu(OAc)2 x H2O as catalyst and oxidant, respectively, to produce the corresponding isocoumarin derivatives.
Abstract: The oxidative coupling of benzoic acids with internal alkynes effectively proceeds in the presence of [Cp*RhCl2]2 and Cu(OAc)2 x H2O as catalyst and oxidant, respectively, to produce the corresponding isocoumarin derivatives. The copper salt can be reduced to a catalytic quantity under air. Interestingly, by using [Cp*IrCl2]2 in place of [Cp*RhCl2]2, the substrates undergo 1:2 coupling accompanied by decarboxylation to afford naphthalene derivatives exclusively. In this case, Ag2CO3 acts as an effective oxidant.

475 citations


Journal ArticleDOI
TL;DR: A field of chemistry that herein is entitled "Supramolecular Analytical Chemistry" is emerging, and is predicted to undergo increasingly rapid growth in the near future.
Abstract: A large fraction of the field of supramolecular chemistry has focused in previous decades upon the study and use of synthetic receptors as a means of mimicking natural receptors. Recently, the demand for synthetic receptors is rapidly increasing within the analytical sciences. These classes of receptors are finding uses in simple indicator chemistry, cellular imaging, and enantiomeric excess analysis, while also being involved in various truly practical assays of bodily fluids. Moreover, one of the most promising areas for the use of synthetic receptors is in the arena of differential sensing. Although many synthetic receptors have been shown to yield exquisite selectivities, in general, this class of receptor suffers from cross-reactivities. Yet, cross-reactivity is an attribute that is crucial to the success of differential sensing schemes. Therefore, both selective and nonselective synthetic receptors are finding uses in analytical applications. Hence, a field of chemistry that herein is entitled "Supramolecular Analytical Chemistry" is emerging, and is predicted to undergo increasingly rapid growth in the near future.

456 citations


Journal ArticleDOI
TL;DR: In this article, the authors discuss progress in the design, synthesis, and functioning of photochemical and electrochemical switches and chemical and light-driven molecular motors and discuss the anchoring of molecular motors on surfaces and molecular motors at work.
Abstract: Molecular switches and motors are essential components of artificial molecular machines. In this perspective, we discuss progress in our design, synthesis, and functioning of photochemical and electrochemical switches and chemical and light-driven molecular motors. Special emphasis is given to the control of a range of functions and properties, including luminescence, self-assembly, motion, color, conductance, transport, and chirality. We will also discuss our efforts to control mechanical movement at the molecular level, a feature that is at the heart of molecular motors and machines. The anchoring of molecular motors on surfaces and molecular motors at work are discussed.

438 citations


Journal ArticleDOI
TL;DR: Employing ethyl 2-oxocyclohexanecarboxylate as a novel, efficient, and versatile ligand, the copper-catalyzed coupling reactions of various N/O/S nucleophilic reagents with aryl halides could be successfully carried out under mild conditions.
Abstract: Employing ethyl 2-oxocyclohexanecarboxylate as a novel, efficient, and versatile ligand, the copper-catalyzed coupling reactions of various N/O/S nucleophilic reagents with aryl halides could be successfully carried out under mild conditions. A variety of products including N-arylamides, N-arylimidazoles, aryl ethers, and aryl thioethers were synthesized in good to excellent yields.

413 citations


Journal ArticleDOI
TL;DR: In this article, the enthalpies of formation for various Lewis acid complexes with representative unsaturated compounds (aldehydes, imines, alkynes, and alkenes) provide a means to evaluate the applicability of a particular catalyst in a catalytic reaction.
Abstract: Computed enthalpies of formation for various Lewis acid complexes with representative unsaturated compounds (aldehydes, imines, alkynes, and alkenes) provide a means to evaluate the applicability of a particular catalyst in a catalytic reaction. As expected, main group Lewis acids such as BX3 show much stronger complexes with heteroatoms than with carbon−carbon multiple bonds (σ-electrophilic Lewis acids). Gold(I) and copper(I) salts with non-nucleophilic anions increase the relative strength of coordination to the carbon−carbon multiple bonds (π-electrophilic Lewis acids). As representative examples for the use of σ-electrophilic Lewis acids in organic synthesis, the Lewis acid mediated allylation reactions of aldehydes and imines with allylic organometallic reagents which give the corresponding homoallyl alcohols and amines, respectively, are mentioned. The allylation method is applied for the synthesis of polycyclic ether marine natural products, such as hemibrevetoxin B, gambierol, and brevetoxin B. A...

341 citations


Journal ArticleDOI
TL;DR: Interestingly, the different inhibition abilities of F-, CH3COO-, and H2PO4- produce different spectral behaviors in PUBO, so this new sensor successfully distinguishes the subtle difference in these three anionic substrates of similar basicity and surface charge density.
Abstract: Condensation of 2-(2‘-aminophenyl)benzoxazole with p-toluenesulfonyl chloride and phenyl isocyanate yields two new anion sensors (TABO and PUBO), which can undergo excited-state intramolecular proton transfer (ESIPT) upon excitation. For the acid receptor TABO, the ESIPT process can be readily disturbed by basic anions such as F-, CH3COO-, and H2PO4- by deprotonating the sulfonamide unit, whereas in the case of PUBO, a good hydrogen-bonding donor, the ESIPT process is inhibited either by the fluoride-induced deprotonation of the urea unit or by the formation of a strong CH3COO-−urea intermolecular hydrogen bond complex, and these two types of inhibition mechanisms consequently result in different ratiometric responses. But other anions with less hydrogen-bonding acceptor abilities cannot inhibit the ESIPT. Interestingly, the different inhibition abilities of F-, CH3COO-, and H2PO4- produce different spectral behaviors in PUBO, so this new sensor successfully distinguishes the subtle difference in these th...

327 citations


Journal ArticleDOI
TL;DR: The Mg(ClO4)2-catalyzed alpha-aminophosphonate synthesis in the present study perhaps represents a true three-component reaction as no intermediate formation of either an imine or alpha-hydroxy phosphonate was observed that indicated the simultaneous involvement of the carbonyl compound, the amine, and the phosphite in the transition state.
Abstract: Commercially available magnesium perchlorate is reported as an extremely efficient catalyst for the synthesis of α-aminophosphonates. A three-component reaction (3-CR) of an amine, an aldehyde or a ketone, and a di-/trialkyl phosphite (Kabachnik−Fields reaction) took place in one pot under solvent-free conditions to afford the corresponding α-aminophosphonates in high yields and short times. The use of solvent retards the rate of the reaction and requires a much longer reaction time than that for neat conditions. The reactions involving an aldehyde, an aromatic amine without any electron-withdrawing substituent, and a phosphite are carried out at rt. The reactions involving cyclic ketones, aromatic amines with an electron-withdrawing substituent, and aryl alkyl ketone (e.g., acetophenone) require longer reaction times at rt or heating. Magnesium perchlorate was found to be superior to other metal perchlorates and metal triflates during the reaction of 4-methoxybenzaldehyde, 2,4-dinitroaniline, and dimethy...

278 citations


Journal ArticleDOI
TL;DR: It was found that the inexpensive CuI/DABCO catalytic system was effective for Sonogashira cross-couplings of aryl halides and vinyl halides.
Abstract: In the presence of TBAB, CuI-catalyzed Suzuki−Miyaura cross-coupling of vinyl halides and aryl halides with arylboronic acids was conducted smoothly to afford the corresponding diarylethenes and polyaryls in moderate to good yields using DABCO (1,4-diazabicyclo[2.2.2]octane) as the ligand. We also found that the inexpensive CuI/DABCO catalytic system was effective for Sonogashira cross-couplings of aryl halides and vinyl halides. A variety of aryl halides and vinyl halides including activated aryl chlorides underwent the coupling with terminal alkynes in moderate to excellent yields.

265 citations


Journal ArticleDOI
TL;DR: This article describes the methodology for a copper-catalyzed preparation of numerous monochalcogenides from dichalCogenides with organoboronic acids using a copper catalyst in air.
Abstract: This article describes the methodology for a copper-catalyzed preparation of numerous monochalcogenides from dichalcogenides with organoboronic acids. Unsymmetrical diorgano-monosulfides, selenides, and tellurides can be synthesized by the coupling of dichalcogenides with aryl- or alkylboronic acids using a copper catalyst in air. The present reaction can take advantage of both organochalcogenide groups on dichalcogenide.

255 citations


Journal ArticleDOI
TL;DR: 4,7-Dimethoxy-1,10-phenanthroline (L1c) was found to be an efficient ligand for the copper-catalyzed N-arylation of imidazole and benzimidazoles with both aryl iodides and bromides under mild conditions and the addition of poly(ethylene glycol) accelerates this reaction.
Abstract: 4,7-Dimethoxy-1,10-phenanthroline (L1c) was found to be an efficient ligand for the copper-catalyzed N-arylation of imidazoles and benzimidazoles with both aryl iodides and bromides under mild conditions. Further optimization of the system has revealed that the addition of poly(ethylene glycol) accelerates this reaction. A variety of hindered and functionalized imidazoles, benzimidazoles, and aryl halides were transformed in good to excellent yields. Heteroaryl halides were also coupled in moderate to good yields. We also present the results obtained from a series of coupling reactions, which directly compare the use of L1c with other recently reported ligands.

Journal ArticleDOI
TL;DR: The Suzuki-Miyaura couplings were used to generate 12 substituted o-terphenyl derivatives and calculations predict the Scholl reaction in alkoxyarenes to proceed via arenium cations, not radical cations.
Abstract: Guidelines for the application of the Scholl reaction were developed. Labeling experiments demonstrate that the Scholl reaction fails in small, unsubstituted oligophenylenes (e.g., o-terphenyl) due to oligomerization of the products (e.g., triphenylene). Incorporation of suitably placed blocking groups (e.g., t-butyl) suppresses oligomerization. The well-established directing group effects in electrophilic aromatic substitution predict the outcome of Scholl reactions of substituted substrates. Activating o,p-directing groups (e.g., MeO) direct bond formation o,p, either intramolecularly or intermolecularly. Deactivating o,p-directing groups (e.g., Br) also direct bond formation o,p but yields are lower. Deactivating m-directors (e.g., NO2) suppress reaction. MoCl5 and PhI(OOCCF3)2/BF3·Et2O are general and effective reagents for the Scholl oxidation. Calculations (B3LYP/6-31G(d)) predict the Scholl reaction in alkoxyarenes to proceed via arenium cations, not radical cations. Suzuki−Miyaura couplings were u...

Journal ArticleDOI
TL;DR: Through structure derivation and a series of NMR studies, the unique role of the 2-picolyl group (the part in red in the abstract graphic) in the sensor 1a-Cd2+ complexation was disclosed.
Abstract: In a neutral aqueous environment, a new ratiometric Cd2+ fluorescent sensor 1a can successfully discriminate Cd2+ from Zn2+ by undergoing two different internal charge transfer (ICT) processes, and the high selectivity of sensor 1a to Cd2+ over some other metals was also observed. Moreover, through structure derivation and a series of NMR studies, the unique role of the 2-picolyl group (the part in red in the abstract graphic) in the sensor 1a-Cd2+ complexation was disclosed.

Journal ArticleDOI
TL;DR: The kinetics of the reactions of 26 primary and secondary amines with benzhydrylium ions in water were investigated photometrically and it is found that secondary alkyl amines and anilines are considerably more nucleophilic, while ammonia is much less nucleophile than expected on the basis of their pKaH values.
Abstract: The kinetics of the reactions of 26 primary and secondary amines with benzhydrylium ions in water were investigated photometrically. Because the parallel reactions of the benzhydrylium ions with hydroxide and water are much slower, the second-order rate constants for the reactions of amines with benzhydrylium ions could be determined reliably. Reactivities of anilines were also studied in acetonitrile solution. Plots of log k2,N for these reactions vs the electrophilicity parameters E of the benzhydrylium ions were linear, which allowed us to derive the nucleophilicity parameters N and s for amines as defined by the equation log k(20 degrees C)=s(E+N). Because the slope parameters for the different amines are closely similar; the relative nucleophilicities are almost independent of the electrophiles and can be expressed by the nucleophilicity parameters N. The correlation between nucleophilicity N and pKaH values is poor, and it is found that secondary alkyl amines and anilines are considerably more nucleophilic, while ammonia is much less nucleophilic than expected on the basis of their pKaH values.

Journal ArticleDOI
TL;DR: It is found that only triple-zeta quality AO basis sets provide results close enough to the basis set limit and that sets like the popular 6-31G(d) should be avoided in accurate work.
Abstract: The reaction energies for 34 typical organic isomerizations including oxygen and nitrogen heteroatoms are investigated with modern quantum chemical methods that have the perspective of also being applicable to large systems. The experimental reaction enthalpies are corrected for vibrational and thermal effects, and the thus derived “experimental” reaction energies are compared to corresponding theoretical data. A series of standard AO basis sets in combination with second-order perturbation theory (MP2, SCS-MP2), conventional density functionals (e.g., PBE, TPSS, B3-LYP, MPW1K, BMK), and new perturbative functionals (B2-PLYP, mPW2-PLYP) are tested. In three cases, obvious errors of the experimental values could be detected, and accurate coupled-cluster [CCSD(T)] reference values have been used instead. It is found that only triple-ζ quality AO basis sets provide results close enough to the basis set limit and that sets like the popular 6-31G(d) should be avoided in accurate work. Augmentation of small bas...

Journal ArticleDOI
TL;DR: Depending on the aldehyde and thiol types, diverse libraries of medicinally relevant compounds can be prepared by a simple one-step process involving no chromatography.
Abstract: Heterocyclic privileged medicinal scaffolds involving pyridine, 1,4-dihydropyridine, chromeno[2,3-b]pyridine, and dihydro-1,4-dithiepine frameworks are prepared via a single-step multicomponent reaction of structurally diverse aldehydes with various thiols and malononitrile. Mechanistic studies of the synthetic pathway leading to pyridines reveal that 1,4-dihydropyridines undergo oxidation by the intermediate Knoevenagel adducts rather than by air oxygen. The use of o,o‘-disubstituted aromatic aldehydes leads to the corresponding 1,4-dihydropyridines, whereas salicylic aldehydes result in chromeno[2,3-b]pyridines. Reactions of ethanedithiol as a thiol component produce dimeric pyridines with sterically unencumbered aldehydes, while o,o‘-disubstituted aromatic aldehydes give dihydro-1,4-dithiepines. Thus, depending on the aldehyde and thiol types, diverse libraries of medicinally relevant compounds can be prepared by a simple one-step process involving no chromatography.

Journal ArticleDOI
TL;DR: A profound halide effect was uncovered, affecting both the efficiency and regioselectivity of indole arylation, and this new and operationally simple procedure provides a rapid entry to a wide range of C-arylated (N-H)-indoles including derivatives of tryptamine.
Abstract: This paper describes a phosphine-free palladium-catalyzed method for direct C-arylation of free (N−H)-indoles and pyrroles with iodo- and bromoarene donors. Employing commercially available materials, this new and operationally simple procedure provides a rapid entry to a wide range of C-arylated (N−H)-indoles including derivatives of tryptamine. In the course of this study, a profound halide effect was uncovered, affecting both the efficiency and regioselectivity of indole arylation.

Journal ArticleDOI
TL;DR: Computational studies (DFT) on imide substituent rotation in PDIs reveal that in the case of bulky groups there is a restricted rotation leading to isomers, in agreement with experimental results.
Abstract: A novel method for the bromination of perylene diimides, PDI (1), under mild conditions is reported. Variation of the reaction conditions allows mono- and dibromination of PDIs to afford 2 and 3 (these can be separated through standard procedures) or exclusive dibromination to afford 3. Pure 1,7 regioisomers are obtained through repetitive crystallization. The structure of 1,7-3b was elucidated by a single-crystal X-ray analysis. The facility of the bromination reaction, which decreases in the order 1a > 1b > 1c, depends on PDI aggregation propensities. Monobrominated PDIs were utilized for the syntheses of novel unsymmetrical piperidinyl (4a and 4b) and trimethylsilylethynyl derivatives (5a and 5b). Computational studies (DFT) on imide substituent rotation in PDIs reveal that in the case of bulky groups there is a restricted rotation leading to isomers, in agreement with our experimental results. An aromatic core twist in PDIs bearing one and two bromine substituents was also investigated by DFT.

Journal ArticleDOI
TL;DR: The synthesis and the spectroscopic studies of the amidourea based calix[4]arene sensors 1 and 2 are described and it is shown that ions such as phosphate were bound in 1:1 stoichiometry, whereas the "urea" protons were shown to be significantly affected upon coordination to the anion.
Abstract: The synthesis and the spectroscopic studies of the amidourea based calix[4]arene sensors 1 and 2 are described. The 4-nitrophenyl based sensor 1 was synthesized in two steps from the corresponding calix [4]arene tetraethyl ester and shown to give rise to color changes in the UV−vis spectra in DMSO upon recognition of pyrophosphate and fluoride. Fitting the changes in the absorption spectra using nonlinear regression analysis indicated strong binding of several anions by 1 such as acetate and hydrogen phosphate in 1:1 (Host:Guest) stoichiometry, and at higher concentration in 1:2 stoichiometry. The preorganized calix-cavity was, however, not found to host chlorine while binding of bromide was determined. At high concentrations of these anions, significant colorimetric changes were also observed that were clearly visible to the naked eye for both pyrophosphate and fluoride. The phenyl analogue 2 was made to enable analysis of the anion recognition using 1H NMR titrations and showed that ions such as phospha...

Journal ArticleDOI
TL;DR: A novel calix[4]arene-based chemosensor 1 based on Hg2+-induced fluorescence resonance energy transfer (FRET) was synthesized, and its sensing behavior toward metal ions was investigated by UV/vis and fluorescence spectroscopies.
Abstract: A novel calix[4]arene-based chemosensor 1 based on Hg2+-induced fluorescence resonance energy transfer (FRET) was synthesized, and its sensing behavior toward metal ions was investigated by UV/vis and fluorescence spectroscopies. Addition of Hg2+ to a CH3CN solution of 1 gave a significantly enhanced fluorescence at ∼575 nm via energy transfer (FRET-ON) from the pyrenyl excimer to a ring-opened rhodamine moiety. In contrast, addition of Al3+ induced a distinct increase of pyrenyl excimer emission (∼475 nm), while no obvious FRET-ON phenomenon was observed. Different binding behaviors of 1 toward Hg2+ and Al3+ were also proposed for the interesting observation.

Journal ArticleDOI
TL;DR: This work provides new, complementary evidence for the repulsive character of the H-H interactions in phenanthrene's bay region and falsify one of the core concepts of the theory of atoms-in-molecules (AIM), namely, that the presence of bond paths and the existence of bond critical points are sufficient indicators for a stabilizing interaction.
Abstract: The enhanced stability of bent or kinked polycyclic benzenoids over linear ones is well established, phenanthrene and anthracene being archetypal representatives. The question why kinked is more stable than linear is, however, still a matter of discussion. Recently, it has been proposed that H-H bonding interactions between the two hydrogen atoms in the bay region of phenanthrene are responsible for the larger stability of this molecule as compared to anthracene. This conclusion conflicts with the vast body of evidence for nonbonded steric repulsion between these hydrogen atoms. In this work, we provide new, complementary evidence for the repulsive character of the H-H interactions in phenanthrene's bay region. We have traced the origin of phenanthrene's enhanced stability to the more efficient bonding in the pi-electron system using, among others, a quantitative energy decomposition analysis of the bonding between the two constituting 2-methtriyl-phenyl fragments in both phenanthrene and anthracene (i.e., C14H10 = C6H4*-CH** + C6H4*-CH**). The scope of our study is extended to polycyclic benzenoids by analyzing also hexacene and various bent isomers of the latter. Our results once more falsify one of the core concepts of the theory of atoms-in-molecules (AIM), namely, that the presence of bond paths and the presence of bond critical points (they exist indeed between the two bay H atoms in phenanthrene) are sufficient indicators for a stabilizing interaction. Instead, our results confirm that these AIM parameters merely diagnose the proximity or contact between charge distributions, be this contact stabilizing or destabilizing.

Journal ArticleDOI
TL;DR: In situ generation of molecular hydrogen by addition of triethylsilane to palladium-charcoal catalyst results in rapid and efficient reduction of multiple bonds, azides, imines, and nitro groups, as well as benzyl group and allyl group deprotection under mild, neutral conditions.
Abstract: In situ generation of molecular hydrogen by addition of triethylsilane to palladium-charcoal catalyst results in rapid and efficient reduction of multiple bonds, azides, imines, and nitro groups, as well as benzyl group and allyl group deprotection under mild, neutral conditions.

Journal ArticleDOI
TL;DR: An environmentally benign synthetic approach to nucleophilic substitution reactions of alcohols that minimizes or eliminates the formation of byproducts, resulting in a highly atom-efficient chemical process.
Abstract: We have developed an environmentally benign synthetic approach to nucleophilic substitution reactions of alcohols that minimizes or eliminates the formation of byproducts, resulting in a highly ato...

Journal ArticleDOI
TL;DR: The mechanism of the oxidation of primary and secondary alcohols by the oxoammonium cation derived from 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) has been investigated computationally at the B3LYP/6-31+G* level, along with free energies of solvation, using a reaction field model.
Abstract: The mechanism of the oxidation of primary and secondary alcohols by the oxoammonium cation derived from 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) has been investigated computationally at the B3LYP/6-31+G* level, along with free energies of solvation, using a reaction field model. In basic solution, the reaction involves formation of a complex between the alkoxide anion and the oxoammonium cation in a pre-oxidation equilibrium wherein methoxide leads to a much larger formation constant than isopropoxide. The differences in free energy of activation for the rate-determining hydrogen transfer within the pre-oxidation complexes were small; the differences in complex formation constants lead to a larger rate of reaction for the primary alcohol, as is observed experimentally. In acidic solution, rate-determining hydrogen atom transfer from the alcohol to the oxoammonium cation had a large unfavorable free energy change and would proceed more slowly than is observed. A more likely path involves a hydride tran...

Journal ArticleDOI
TL;DR: The present study has demonstrated that the exceedingly reactive CF(3) oxonium species can be generated much easier than the CH(3)+ species, contrary to the common sense that CF( 3)+ is extremely difficult to generate in solution.
Abstract: We report in situ synthesis of the first CF3 oxonium salts, thermally unstable O-(trifluoromethyl)dibenzofuranium salts, which furthermore have different counteranions (BF4-, PF6-, SbF6-, and Sb2F11-) and ring substituents (tert-butyl, F, and OCH3), by photochemical decomposition of the corresponding 2-(trifluoromethoxy)biphenylyl-2‘-diazonium salts at −90 to −100 °C. The yields markedly increased in the order of BF4- < PF6- < SbF6- < Sb2F11-. The CF3 oxonium salts were fully assigned by means of 1H and 19F NMR spectroscopy at low temperature. The CF3 salts decomposed to form CF4 and dibenzofurans. The half-life times at −60 °C of the 2-tert-butyl salts having different counteranions were 29 min for BF4- salt 2d, 36 min for PF6- salt 2c, 270 min for SbF6- salt 2a, and 415 min for Sb2F11- salt 2b. Those at −60 °C of the Sb2F11- salts having different 2-substituents were 13 min for F salt 3b, 63 min for H (unsubstituted) salt 1b, and 415 min for tert-butyl salt 2b. Thus, the stability of the CF3 oxonium sal...

Journal ArticleDOI
TL;DR: A concise and efficient synthesis of 1,3-disubstituted 1,2-dihydroisoquinolines has been achieved via tandem nucleophilic addition and cyclization of 2-(1-alkynyl)arylaldimines.
Abstract: By using carbophilic Lewis acids, In(OTf)3, NiCl2, and AuCl(PPh3)/AgNTf2, a concise and efficient synthesis of 1,3-disubstituted 1,2-dihydroisoquinolines has been achieved via tandem nucleophilic addition and cyclization of 2-(1-alkynyl)arylaldimines. Addition of proton sources such as water, CF3CH2OH, and 2,6-di-tert-butyl-4-methoxyphenol was essential for the Lewis acid-catalyzed tandem reactions with organometallic reagents. By switching these catalysts, various types of nucleophiles such as allylstannanes, silyl enol ethers, alkenylboronic acids, and active methylene compounds could be introduced at the C1 position of 1,2-dihydroisoquinolines in this transformation. Furthermore, this method proved to be applicable to the synthesis of 1H-isochromene derivatives via the same tandem reaction of 2-(1-alkynyl)arylaldehydes.

Journal ArticleDOI
TL;DR: For all of the studied (S)-proline-catalyzed asymmetric Mannich- and aldol-type reactions, the observed rate enhancements were a consequence of the increased temperatures attained by microwave dielectric heating and were not related to the presence of the microwave field.
Abstract: A series of five known asymmetric organocatalytic reactions was re-evaluated at elevated temperatures applying both microwave dielectric heating and conventional thermal heating in order to probe the existence of specific or nonthermal microwave effects. All transformations were conducted in a dedicated reactor setup that allowed accurate internal reaction temperature measurements using fiber-optic probes. In addition, the concept of simultaneous external cooling while irradiating with microwave power was also applied in all of the studied cases. This method allows a higher level of microwave power to be administered to the reaction mixture and, therefore, enhances any potential microwave effects while continuously removing heat. For all of the five studied (S)-proline-catalyzed asymmetric Mannich- and aldol-type reactions, the observed rate enhancements were a consequence of the increased temperatures attained by microwave dielectric heating and were not related to the presence of the microwave field. In...

Journal ArticleDOI
TL;DR: These studies explain not only the narrow polydispersity index (PDI) observed in the ROP of six-membered ring lactones, but also the surprising failure of the Rop for the more reactive butyrolactone.
Abstract: Triazabicyclodecene (TBD) has recently been shown to be an effective organocatalyst for the ring-opening polymerization (ROP) of cyclic esters. Using DFT methods, we have studied possible mechanisms of this reaction. Our studies explain not only the narrow polydispersity index (PDI) observed in the ROP of six-membered ring lactones, but also the surprising failure of the ROP for the more reactive butyrolactone.

Journal ArticleDOI
TL;DR: In this article, the pKa values of 16 1,3-dialkylimidazolium-type ionic liquid (IL) molecules were systematically measured by the overlapping indicator method at 25 °C in dimethyl sulfoxide (DMSO) solution.
Abstract: Equilibrium acidities of 16 1,3-dialkylimidazolium-type ionic liquid (IL) molecules (1−16) were systematically measured by the overlapping indicator method at 25 °C in dimethyl sulfoxide (DMSO) solution. The pKa values were observed to range from 23.4 for IL 12 to 19.7 for IL 6 (Tables 1 and 2), responding mainly to structural variations on the cation moiety. Excellent agreement between the spectrophotometrically determined pKa and that derived from NMR titration for 1,3,4,5-tetramethylimidazolium bis(trifluoromethanesulfonyl)imide (12) and the close match of the obtained pK values with the reported data in literature provide credence to the acidity measurements of the present work. The substituent effects at the imidazolium ring and the effects of counterions on the acidities of ionic liquids are discussed.

Journal ArticleDOI
TL;DR: First time, for the first time, the one-step alkylation of dimedone and 1,3-cyclohexanedione with aldehydes and Hantzsch ester is developed through an organocatalytic reductiveAlkylation strategy.
Abstract: A practical and novel organocatalytic chemo- and enantioselective process for the cascade synthesis of highly substituted 2-alkyl-cyclohexane-1,3-diones and Wieland−Miescher (W−M) ketone analogs is presented via reductive alkylation as a key step. First time, we developed the one-step alkylation of dimedone and 1,3-cyclohexanedione with aldehydes and Hantzsch ester through an organocatalytic reductive alkylation strategy. Direct combination of l-proline-catalyzed cascade Knoevenagel/hydrogenation and cascade Robinson annulation of CH acids (dimedone and 1,3-cyclohexanedione), aldehydes, Hantzsch ester, and methyl vinyl ketone furnished the highly functionalized W−M ketone analogues in good to high yields and with excellent enantioselectivities. Many of the reductive alkylation products show a direct application in pharmaceutical chemistry.