Rhodium(I)‐Catalyzed Cycloisomerization of Benzylallene‐Alkynes through C?H Activation

The efficient Rh^I‐catalyzed cycloisomerization of benzylallene‐alkynes produced the tricyclo[9.4.0.0^3,8]pentadecapentaene skeleton through a C H bond activation in good yields. A plausible reaction mechanism proceeds via oxidative addition of the acetylenic C H bond to Rh^I, an ene‐type cyclization to the vinylidenecarbene–Rh^I intermediate, and an electrophilic aromatic substitution with the vinylidenecarbene species. It was proposed based on deuteration and competition experiments.     

Aryl‐Copper(III)‐Acetylides as Key Intermediates in CCsp Model Couplings under Mild Conditions

The mechanism of copper‐mediated Sonogashira couplings (so‐called Stephens–Castro and Miura couplings) is not well understood and lacks clear comprehension. In this work, the reactivity of a well‐defined aryl‐Cu^III species ( 1 ) with p‐R‐phenylacetylenes (R=NO₂, CF₃, H) is reported and it is found that facile reductive elimination from a putative aryl‐Cu^III‐acetylide species occurs at room temperature to afford the C_aryl?C_sp coupling species ( I_R ), which in turn undergo an intramolecular reorganisation to afford final heterocyclic products containing 2H‐isoindole ( P , P , P_Ha ) or 1,2‐dihydroisoquinoline ( P_Hb ) substructures. Density Functional Theory (DFT) studies support the postulated reductive elimination pathway that leads to the formation of C?C_sp bonds and provide the clue to understand the divergent intramolecular reorganisation when p‐H‐phenylacetylene is used. Mechanistic insights and the very mild experimental conditions to effect C_aryl?C_sp coupling in these model systems provide important insights for developing milder copper‐catalysed C_aryl?C_sp coupling reactions with standard substrates in the future.     

Trans‐Selective Radical Silylzincation of Ynamides

The silylzincation of terminal ynamides is achieved through a radical‐chain process involving (Me₃Si)₃SiH and R₂Zn. A potentially competing polar mechanism is excluded on the basis of diagnostic control experiments. The unique feature of this addition across the CC bond is its trans selectivity. One‐pot electrophilic substitution of the C Zn bond by Cu^I‐mediated C C bond formation and subsequent manipulation of the C Si bond provides a modular access to Z‐α,β‐disubstituted enamides.     

Copper‐Catalyzed Aerobic Oxidative NS Bond Functionalization for CS Bond Formation: Regio‐ and Stereoselective Synthesis of Sulfones and Thioethers

A regio‐ and stereoselective synthesis of sulfones and thioethers by means of Cu^I‐catalyzed aerobic oxidative N?S bond cleavage of sulfonyl hydrazides, followed by cross‐coupling reactions with alkenes and aromatic compounds to form the C?S bond, is described herein. N₂ and H₂O are the byproducts of this transformation, thus offering an environmentally benign process with a wide range of potential applications in organic synthesis and medicinal chemistry.     

Rhodium(III)‐Catalyzed Activation of C?H Bonds and Subsequent Intermolecular Amidation at Room Temperature

Disclosed herein is a Rh^III‐catalyzed chelation‐assisted activation of unreactive C H bonds, thus enabling an intermolecular amidation to provide a practical and step‐economic route to 2‐(pyridin‐2‐yl)ethanamine derivatives. Substrates with other N‐donor groups are also compatible with the amidation. This protocol proceeds at room temperature, has a relatively broad functional‐group tolerance and high selectivity, and demonstrates the potential of rhodium(III) in the promotive functionalization of unreactive C H bonds. A rhodacycle having a SbF₆⁻ counterion was identified as a plausible intermediate.     

Transition‐Metal‐Catalyzed CH Bond Functionalizations: Feasible Access to a Diversity‐Oriented β‐Carboline Library

Diversification of the β‐carboline skeleton has been demonstrated to assemble a β‐carboline library starting from the tetrahydro‐β‐carboline framework. This strategy affords feasible access to heteroaryl‐, aryl‐, alkenyl‐, or alkynyl‐substituted β‐carbolines at the C1, C3, or C8 position through three categorically different types of transition‐metal‐catalyzed C?C bond‐forming reactions, in the presence of multiple potentially reactive positions. These site‐selective functionalizations include; 1) the Cu‐catalyzed C1/C3‐selective decarboxylative C?C and C?C_sp coupling of hexahydro‐β‐carboline‐3‐carboxylic acid with a C?H bond of a heteroarene or terminal alkyne; 2) the chelation‐assisted Pd‐catalyzed C1/C8‐selective C?H arylation of hexahydro‐β‐carboline with aryl boron reagents; and 3) the chelation‐assisted Pd‐catalyzed C1/C3‐selective oxidative C?H/C?H cross‐coupling of β‐carboline‐N‐oxide with arenes, heteroarenes, or alkenes. The saturated structural feature of the hexahydro‐β‐carboline framework can increase reactivity and control site selectivity. The robustness of these approaches has been demonstrated through the synthesis of hyrtioerectine analogues and perlolyrine. We believe that these strategies could provide inspiration for late‐stage diversifications of bioactive core scaffolds.     

Small Molecule Activation by POCOP‐Nickel Complexes

This contribution describes the reactivities of CO₂, CO, O₂, and ArNC with the pincer‐type complexes [(κ^P,κ^C,κ^P′‐POCOP)NiX] (POCOP=(R₂POCH₂)₂CH; R=iPr; X=OSiMe₃, NArH; Ar=2,6‐iPr₂C₆H₃). Reaction of the amido derivative with CO₂ and CO leads to a simple insertion into the Ni?N bond to give stable carbamate and carbamoyl derivatives, respectively, the pincer ligand backbone remaining intact in both cases. In contrast, the analogous reactions with the siloxide derivative produced kinetically labile insertion products that either revert to the starting material (in the case of CO₂) or react further to give the mixed‐valent, dinickel species [(POCOP)Ni^II{μ,κ^O,κ^P,κ^P′‐OCOCH(CH₂CH₂OPR₂)₂}Ni⁰(CO)₂]. The zero‐valent center in the latter compound is ligated by a new ligand arising from transformation of the POCOP ligand backbone. The carbonylation and carboxylation of the siloxido derivative also produced minor quantities of a side‐product identified as the trinickel species, [{(η³‐allyl)Ni(μ^O,κ^P‐R₂PO)₂}₂Ni], arising from total dismantling of the POCOP ligand. Similar reactivities were observed with isonitrile, ArNC: reaction with the siloxido derivative resulted in a complex sequence of steps involving initial insertion, a 1,3‐hydrogen shift, and an Arbuzov rearrangement to give [Ni(CNAr)₄] and a methacrylamide based on fragments of the POCOP ligand. Oxygenation of the amido and siloxido derivatives led to the phosphinate derivative, [(POCOP)Ni(OP(O)R₂)], arising from oxidative transformation of the original ligand frame; the reaction with the Ni‐NHAr derivative also gave ArHNP(O)R₂ through a complex N?P bond‐forming reaction.     

Ligand‐Promoted ortho‐CH Amination with Pd Catalysts

2,4,6‐Trimethoxypyridine is identified as an efficient ligand for promoting a Pd‐catalyzed ortho‐C? H amination of both benzamides and triflyl‐protected benzylamines. This finding provides guidance for the development of ligands that can improve or enable Pd^II‐catalyzed C? H activation reactions directed by weakly coordinating functional groups.     

Metal‐Porphyrin Orbital Interactions in Paramagnetic Iron Complexes Having Planar and Deformed Porphyrin Ring

¹H and ¹³C NMR chemical shifts of iron porphyrin complexes are determined mainly by the spin densities at the peripheral carbon and nitrogen atoms caused by the interaction between paramagnetic iron 3d and porphyrin molecular orbitals. This review describes how the half‐occupied iron 3d orbitals such as d_π(d_xz, d_yz), d_xy, d, and d‐ interact with a specific porphyrin molecular orbital and affect the ¹H and ¹³C NMR chemical shifts in planar, ruffled, saddled, and domed complexes. Revealing the relationship between the orbital interactions and NMR chemical shifts is quite important to determine the fine electronic structures of synthetic iron porphyrin complexes as well as naturally occurring heme proteins.     

Rhodium(III)‐Catalyzed Activation of C?H Bonds and Subsequent Intermolecular Amidation at Room Temperature

Disclosed herein is a Rh^III‐catalyzed chelation‐assisted activation of unreactive C H bonds, thus enabling an intermolecular amidation to provide a practical and step‐economic route to 2‐(pyridin‐2‐yl)ethanamine derivatives. Substrates with other N‐donor groups are also compatible with the amidation. This protocol proceeds at room temperature, has a relatively broad functional‐group tolerance and high selectivity, and demonstrates the potential of rhodium(III) in the promotive functionalization of unreactive C H bonds. A rhodacycle having a SbF₆⁻ counterion was identified as a plausible intermediate.     

Development of the crystallinity and rigid amorphous fraction in cold‐crystallized isotactic polystyrene

The phase structure of crystalline isotactic polystyrene (iPS) has been investigated with temperature‐modulated differential scanning calorimetry (TMDSC), wide‐angle X‐ray scattering (WAXS), and Fourier transform infrared (FTIR) spectroscopy. Quenched amorphous samples have been cold‐crystallized at 140 or 170 °C for various crystallization times. The degree of crystallinity obtained from WAXS, with the ratio of the crystal peak intensity to the total peak intensity, shows excellent agreement with the crystallinity determined from TMDSC total heat flow endotherms. For the first time, FTIR results show that the absorbance peak ratio (I/I) has a linear correlation with the crystalline mass fraction (χ_c) for cold‐crystallized iPS according to the following relation: I/I = 0.54χ_c + 0.16. This relationship allows the crystallinity of iPS to be determined from infrared spectroscopy analyses in cases in which it is difficult to perform thermal or X‐ray measurements. On the basis of the measurements of the heat capacity increment at the glass transition, we find that a significant amount of the rigid amorphous fraction (RAF) coexists with the crystalline and mobile amorphous phases in cold‐crystallized iPS. The RAF increases systematically with the crystallization time, and a greater amount is formed at a lower crystallization temperature. A three‐phase model (crystalline phase, mobile amorphous phase, and rigid amorphous phase) is, therefore, appropriate for the interpretation of the structure of cold‐crystallized iPS. The origin of the low‐temperature endothermic peak (annealing peak) has been investigated with TMDSC and FTIR spectroscopy and has been shown to be due to irreversible relaxation of the RAF. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3026–3036, 2003     

Tunable Keplerate Type‐Cluster “Mo132” Cavity with Dicarboxylate Anions

The internal functionalization of the Keplerate‐type capsule Mo₁₃₂ has been carried out by ligand exchange leading to the formation of glutarate and succinate containing species isolated as ammonium or dimethylammonium salts. Solution NMR analysis is consistent with asymmetric inner dicarboxylate ions containing one carboxylato group grafted onto the inner side of the spheroidal inorganic shell while the second hangs toward the center of the cavity. Such a disposition has been confirmed by the single‐crystal X‐ray diffraction analysis of the glutarate containing {Mo₁₃₂} species. A detailed NMR solution study of the ligand‐exchange process allowed determining the binding constant K_L of acetate (AcO^?), succinate (HSucc^?) or glutarate (HGlu^?) ligands at the 30 inner coordinating sites, which vary such as K<K<K‐supported by the associated thermodynamic parameters Δ_rS* and Δ_rH*. Such a variation is mainly explained by a positive entropic gain attenuated by unfavorable steric effect. Furthermore, these results are completed by ¹H DOSY and ¹H EXSY NMR experiments which are in agreement with bulky guests firmly trapped within the cavity. At last, variable temperature ¹H NMR study below 290 K revealed a striking line broadening occurring abruptly within a 5 K range. Such an effect appears closely related to the presence of the ammonium cations suspected to be present within the cavity and then has been interpreted as an inner‐phase transition leading to a frozen state.     

The first automated 470.59 MHz 19F NMR‐controlled titration: dissociation constants and ion‐specific chemical shifts of 2‐amino‐4‐fluoro 2‐methylpent‐4‐enoic acid

2‐Amino‐4‐fluoro‐2‐methylpent‐4‐enoic acid, obtained as a 1 : 1 salt with trifluoro‐acetic acid, was characterized by ¹H and ¹⁹F high‐resolution NMR spectroscopy. High‐precision potentiometry led to the dissociation constants pK = 1.879 and pK = 9.054. The first automated 470.59 MHz ¹⁹F NMR‐controlled titration yielded the dynamic chemical shift 〈δ_F〉 as a function of pcH or τ and the ion‐specific chemical shifts: δ_F(H₂L⁺) = ?94.81 ppm, δ_F(HL) = ?94.21 ppm, δ_F(L^?) = ?92.45 ppm. The deprotonation gradients were found to be Δ₁ = ?0.60 ppm and Δ₂ = ?1.76 ppm. Copyright © 2002 John Wiley & Sons, Ltd.     

2–Butoxyethanol and benzyl alcohol reactions with the nitrate radical: Rate coefficients and gas‐phase products

The bimolecular rate coefficients k and k were measured using the relative rate technique at (297 ± 3) K and 1 atmosphere total pressure. Values of (2.7 ± 0.7) and (4.0 ± 1.0) × 10^?15 cm³ molecule^?1 s^?1 were observed for k and k, respectively. In addition, the products of 2‐butoxyethanol + NO₃^? and benzyl alcohol + NO₃^? gas‐phase reactions were investigated. Derivatizing agents O‐(2,3,4,5,6‐pentafluorobenzyl)hydroxylamine and N, O‐bis (trimethylsilyl)trifluoroacetamide and gas chromatography mass spectrometry (GC/MS) were used to identify the reaction products. For 2‐butoxyethanol + NO₃^? reaction: hydroxyacetaldehyde, 3‐hydroxypropanal, 4‐hydroxybutanal, butoxyacetaldehyde, and 4‐(2‐oxoethoxy)butan‐2‐yl nitrate were the derivatized products observed. For the benzyl alcohol + NO₃^? reaction: benzaldehyde ((C₆H₅)C(?O)H) was the only derivatized product observed. Negative chemical ionization was used to identify the following nitrate products: [(2‐butoxyethoxy)(oxido)amino]oxidanide and benzyl nitrate, for 2‐butoxyethanol + NO₃^? and benzyl alcohol + NO₃^?, respectively. The elucidation of these products was facilitated by mass spectrometry of the derivatized reaction products coupled with a plausible 2‐butoxyethanol or benzyl alcohol + NO₃^? reaction mechanisms based on previously published volatile organic compound + NO₃^? gas‐phase mechanisms. © 2012 Wiley Periodicals, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America.

© 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 778–788, 2012     

Chemical actinometry at 147.0 nm

Hexafluoroacetone (HFA) and O₂ were photolyzed at 147.0 nm to investigate their use in chemical actinometry. The products, CO for the former and O₃ in the latter case, were monitored. For accurate comparison, both of these substances were irradiated by a single light source with two identical reaction cells at 180° to each other. The light intensities I were measured under the same integrated as well as instantaneous photon flux based on ? and ?_CO (quantum yield) as 2 and 1, respectively. Optimum conditions for maximum product yield were 5.0 torr HFA pressure and an O₂ flow rate of 200 ml/min at 1 atm pressure for a 20-minute photolysis period. For light intensity variations between 1.09 × 10¹⁴ and 2.10 × 10¹⁵ photons absorbed/sec, the ratio I/I_HFA was found to be unity. Calibration with the commonly used N₂O actinometer for a ? value of 1.41 showed that I/I_HFA and I/I are unity. Both HFA and O₂ are suitable chemical actinometers at 147.0 nm with ?_CO and ? of 1 and 2, respectively. The light intensity determination in the first case involves the measurement of only one product which is noncondensible at 77°K, whereas wet analysis for O₃, the only product, in the second actinometer is necessary. Both of these determinations are quite simple and are preferable over product analysis in N₂O actiometry, wherein N₂ separation from other noncondensibles at 77°K is required.     

Basicity of Phenyl‐ and Methyl‐Substituted 1,2,4‐Oxadiazoles

The basicity of a series of 3,5‐disubstituted 1,2,4‐oxadiazoles in aqueous H₂SO₄ was examined by means of UV and ¹H‐NMR spectroscopy. The experimental data were analyzed by the modified Yates–McClelland method to yield the following pK values: 3,5‐dimethyl‐1,2,4‐oxadiazole, −1.66±0.06; 3‐methyl‐5‐phenyl‐1,2,4‐oxadiazole, −2.61±0.02; 3‐phenyl‐5‐methyl‐1,2,4‐oxadiazole, −2.95±0.01; 3,5‐diphenyl‐1,2,4‐oxadiazole, −3.55±0.06. A pK value of ca. −3.7 was estimated for the parent unsubstituted 1,2,4‐oxadiazole based on substituents' additivity increments. Possible protonation sites of the compounds were discussed in terms of both experimental data and theoretical calculations (HF/6‐31G**). Generally, protonation is most likely to occur at N(4) of the 1,2,4‐oxadiazole ring. However, concurrent formation of both N(4)‐ and N(2)‐protonated species in comparable amounts is possible in the case of 3‐phenyl‐1,2,4‐oxadiazoles.     

Field‐assisted dissociative ionization of CH2I2 induced by femtosecond laser field

The field‐assisted dissociative ionization of CH₂I irradiated by a 60‐fs 800‐nm laser with different laser intensities (1–4 × 10¹⁴ W/cm²) is studied both experimentally and theoretically. The different fragmentation patterns are observed in the experiment with a time‐of‐flight mass spectrometer. In the theoretical aspect, the Gaussian 03 program is applied to calculate the potential energies of CH₂I as functions of the C? I and C? H bond distances and I? C? I bond angle under external field with different intensities. The calculations explain our experimental observations well. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Oxindole Synthesis by Direct Coupling of C?H and C?H Centers

An sp ² /sp ³ get‐together : A novel and efficient method can be used to synthesize 3,3‐disubstitued oxindoles by the direct intramolecular oxidative coupling of an aryl C? H and a C? H center (see scheme; DMF=N,N‐dimethylformamide).

     

Rate constants for the gas‐phase reactions of nitrate radicals with geraniol,citronellol, and dihydromyrcenol

Terpenes and terpene alcohols are prevalent compounds found in a wide variety of consumer products including soaps, flavorings, perfumes, and air fresheners used in the indoor environment. Knowing the reaction rate of these chemicals with the nitrate radical is an important factor in determining their fate indoors. In this study, the bimolecular rate constants of k (16.6 ± 4.2) × 10^?12, k (12.1 ± 3) × 10^?12, and k (2.3 ± 0.6) × 10^?14 cm³ molecule^?1 s^?1 were measured using the relative rate technique for the reaction of the nitrate radical (NO₃?) with 2,6‐dimethyl‐2,6‐octadien‐8‐ol (geraniol), 3,7‐dimethyl‐6‐octen‐1‐ol (citronellol), and 2,6‐dimethyl‐7‐octen‐2‐ol (dihydromyrcenol) at (297 ± 3) K and 1 atmosphere total pressure. Using the geraniol, citronellol, or dihydromyrcenol + NO₃? rate constants reported here, pseudo‐first‐order rate lifetimes (k′) of 1.5, 1.1, and 0.002 h^?1 were determined, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 669–675, 2010     

Acceleration of Reductive Elimination of [Ar‐Pd‐C] by a Phosphine/Electron‐Deficient Olefin Ligand: A Kinetic Investigation

Dramatic rate enhancement of reductive elimination of [Ar‐Pd‐C] was observed in the presence of a phosphine/electron‐deficient olefin ligand. Through systematic kinetic investigations of the Negishi coupling of ethyl 2‐iodobenzoate with alkylzinc chlorides (see scheme), the rate constants for reductive elimination of [Ar‐Pd‐C] were determined to be greater than 0.3 s^?1, which is about four or five orders of magnitude greater than values reported previously.