A 1-hydroxy-2,3,1-benzodiazaborine-containing π-conjugated system: Synthesis,optical properties and solvent-dependent response toward anions

Our interest in the functionalization of OH-substituted azaborines prompted us to synthesize a 1-hydroxy-2,3,1-benzodiazaborine conjugated with 1,8-naphthalimide 1. Its fluorescence was dramatically affected by the nature of the solvent. In particular, the use of DMSO, which has a relatively high donor number (DN = 29.8), led to a remarkable decrease in the fluorescence intensity (Φ_F = 0.0014), possibly due to intermolecular hydrogen-bonding interactions (Me₂SO?HOB). The presence of the hydroxyl group on boron led to a solvent-driven colorimetric response towards anions; high selectivity for F^? over other anions in DMSO, and responded to AcO^? and F^? in THF, as shown by UV/vis titrations, NMR, and mass spectroscopic analysis. The nucleus-independent chemical shift (NICS) indices suggested that hydrogen bonding interactions between Me₂SO and HOB reduced the aromaticity of the benzodiazaborine macrocycle, causing an increase in the negative character of the boron. The increase in the polarity of the BN bond may prevent acetate-binding of 1 in DMSO.     

Insight into hydrogen bonding of terephthalamides with amino acids: Synthesis,structural and spectroscopic investigations

Several bis-terephthalamides based on methyl esters of amino acids including glycine (1), β-alanine (2), γ-aminobutyric acid (3) and ε-aminocaproic acid (4), X(CH₂)_nHNOCC₆H₄CONH(CH₂)_nX (XCO₂CH_3,n = 1, 2, 3 and 5), have been synthesized and characterized by single-crystal X-ray diffraction and spectroscopic methods: FT-IR, polarized FT-IR, Raman, ¹H NMR and ¹³C NMR. The four structures assemble via classical NH?O hydrogen bonds between amide functionalities linking the molecules into chains parallel to the short axis. The analysis of polarized IR spectra of pure and deuterated compounds reveals that a weak interchain (“through-space”) exciton coupling involves two closely-spaced hydrogen bonds belonging to two different adjacent chains. The exciton coupling magnitude decreases with the addition of methylene groups to the terephthalamide system. Isotope effects in terephthalamides show that the distribution of protons and deuterons in the crystalline lattice depends on the strength of the exciton couplings involving hydrogen bonds.     

Perturbation par l''oxygene de l''oxydation anodique De l''anion complexe cr(co)5cn

OsCl₂(CFCl)(CO)(PPh₃)₂ results from reaction between OsCl₂(CCl₂)(CO)(PPh₃)₂ and Cd(CF₃)₂(DME). The CFCl ligand is converted into CFNMe₂ and CFSEt ligands through reaction with Me₂NH and NaSEt, respectively. The crystal structure of RuCl₂(CFOCH₂CMe₃)(CO)(PPh₃)₂ reveals the following dimensions about the carbene-carbon atom: RuC, 1.914(5)Å; CO, 1.303(7)Å; CF, 1.307(6)Å; RuCF, 127.1(4)°; RuCO, 125.5(4)°; FCO, 107.4(5)°.     

Computational study of Rh(I)-Catalyzed Cycloaddition–Fragmentation of N-cyclopropylacrylamides

Rh-catalyzed cycloaddition–fragmentation of N-cyclopropylacrylamides is an effective method to directly obtain substituted azocanes. In this transformation, the challenging step is insertion of CO and alkene into the more hindered proximal cyclopropane CC bond while avoiding competitive less hindered proximal CC activation. Given the importance of this novel strategy, we performed a density functional theory study to clarify the catalytic mechanism. The calculations confirm that cleavage of the more hindered bond is more favorable than cleavage of the less hindered bond for Rh-catalyzed (7 + 1) cycloaddition of N-cyclopropylacrylamides. Comparison between Rh-catalyzed (3 + 1 + 2) and (7 + 1) cycloaddition shows that the coordination mode with different ligand plays a crucial role in enabling different CC cleavage. The main factors responsible for the occurrence of β-hydride elimination rather than CC reductive elimination are also discussed. The kinetic preference for β-hydride elimination can be attributed to the transition state of CC reductive elimination being more distorted and forming in a much more concerted fashion than that of β-hydride elimination. Additionally, C4H elimination is disfavored owing to weaker interaction energy compared with C7H elimination by analyzing using the distortion/interaction model.     

Palladium-catalysed cross-coupling as a key step in the synthesis of pyridyl-benzamides, -benzylamines and -sulfonamides

Novel N-, O- and S-substituted pyridyl-benzamides, -benzylamines and -sulfonamides were prepared by means of palladium-catalysed cross-coupling reactions. The synthetic approach, using Pd₂(dba)₃ as palladium source and rac-BINAP as supporting ligand, proved to be successful for CN, CO and CS cross-coupling reactions. One of the substrates underwent an unexpected nucleophilic aromatic substitution of fluorine, rather than the expected CN cross-coupling reaction.     

Vinyl-aziridines and cyclopropanes in Pd-catalyzed (3+2)-cycloaddition reactions with cyclic N-sulfonyl imines

Efficient palladium-catalyzed (3 + 2)-cycloaddition reactions of cyclic N-sulfonyl imines and vinyl-aziridines (or cyclopropanes) have been achieved. The reactions, with either vinylic substrate, proceed with excellent yields affording highly functionalized imidazolidine and pyrrolidine derivatives. The cycloadditions take place via the reaction of zwitterionic π-allyl palladium intermediates with cyclic N-sulfonyl imines through i) the formation of two NC bonds in the presence of vinylaziridines (synthesis of imidazolidines) and ii) one CC bond and one NC bond in the presence of vinylcyclopropanes (synthesis of pyrrolidines). Following on preliminary works on the diastereoselective synthesis of imidazolidines, herein we wish to give a broader view on the subject by describing derivatization reactions and attempts towards an enantioselective version. Moreover, we describe and discuss the behavior of each vinylic substrate (aziridine or cyclopropane) on the (3 + 2)-cycloaddition reactions. Mechanistic and (intriguing) selectivity outcomes are also going to be discussed.     

Iron-catalyzed CC bond activation/CO bond formation: Direct conversion of ketones to esters

The iron-catalyzed oxidative activation of the (O)CC bond in ketones has been developed. This method enables direct synthesis of esters by the reaction between ketones and alcohols via conversion of the (O)CC bond to the (O)CO bond. The reaction runs selectively: the (O)CC_Alkyl bond is activated, while the (O)CC_Aryl bond remains intact (i.e., iron-catalyzed intermolecular anti-Baeyer-Villiger activation of the (O)CC bond). The reaction conditions are carefully optimized and allow the production of esters with yields of up to 95%. The method is based on the inexpensive and commercially available catalyst (FeCl₃), oxidant ((NH₄)₂S₂O₈), and solvent (DCE) without using any ligands or additives.     

Molecular capsules of tetrakis(N-hydantoinylimino)cavitand: Selective encapsulation of 1,4-diiodobenzene

Resorcin[4]arene-based iminocavitand 2 with four hydantoinyl moieties was designed and synthesized. This cavitand 2 self-assembled into thermally stable molecular capsules G@2₂ in the presence of suitable guests through 8 intermolecular hydrogen bonds of imide NH?OC, two for each four paired hydantoinyl units. Molecular capsule 2₂ showed selective complexation for p-disubstituted benzenes, especially for 1,4-diiodobenzene.     

Novel anion receptors for selective recognition of dimethyl phosphinate and carboxylate

We have designed and synthesized new anion receptors 1 and 2, which have amide NH, pyrrole NH and vinyl CH as hydrogen bond donors. These receptors are selective for dimethyl phosphinate and carboxylates. Due to electron withdrawing effect of the cyano group which is trans to the vinyl hydrogen with respect to carbon-carbon double bond, receptor 1 has higher binding constants for phosphinate and carboxylate than those of receptor 2. Modeling studies shows that cyano group polarized all three hydrogens through planar π-electron network. In addition, receptor 1 gave orange colored 1,4-addition product for cyanide.     

Pathways of cycloaddition of carbodiimides to N-alkenylidenetriflamides: A theoretical study

Possible cyclization pathways for the reaction of (1E,2E)-N-(but-2-en-1-ylidene)triflamide with N,N'-dimethylcarbodiimide have been investigated by DFT and MP2 calculations. The [4+2] route is shown to be thermodynamically unfavorable due to a small content of the reactive s-cis conformer of the azadiene. The [2_CN+2_CN] route has ΔGº>0 and therefore is thermodynamically forbidden. The only allowed route is the [2_CN+2_CC] cycloaddition, which has ΔGº < 0 and leads to 2-methylimino-3-(2-trifliminomethyl)-1,4-dimethylazetidine with further isomerization to 3-(triflamidomethylidene)-2-methylimino-1,4-dimethylazetidine in full agreement with the experimental results. These results indicate the necessity of considering free energy changes rather than only enthalpy changes for accurate prediction of the course of cyclization reactions.     

Metal-(phenylthio)alkanoic acid interactions— VII. The crystal and molecular structures of diaquabis[(benzylthio)acetato]-zinc(II), catena- [diaqua-tetra[(benzylthio)acetato]-bis[cadmium(II)], catena-tetra-μ-{2-methyl-3- (phenylthio)propionato-O,O′]-bis[copper(II)]} and tetra-μ-[2-methyl-2-(phenylthio)propionato-O,O′]- bis[ethanolcopper(II)]

The crystal structures of diaquabis[(benzylthio)acetato]zinc(II), [Zn(BTA)₂ (H₂O)₂] (1), catena-[diaqua-tetra[(benzylthio)acetato)]-bis[cadmium(II)], [Cd₂(BTA)₄ H₂O)₂]_n (2), catena-{tetra-μ-[2-methyl-3-(phenylthio)propionato-O,O′]-bis[copper (II)]}, [Cu₂(MPTP)₄]_n (3) and tetra-μ-[2-methyl-2-(phenylthio)propionato-O,O′]- bis[ethanol copper(II)], [Cu₂(PTIBA)₄(EtOH)₂] (4) have been determined using X-ray diffraction techniques. Complex (1) is monomeric with distorted octahedral stereochemistry and lies on a two-fold rotational axis. The MO₆ coordination involves four oxygens from two slightly asymmetric bidentate BTA car☐yl groups [ZnO, 2.138(3), 2.28(3)Å] and two cis-related waters [ZnOw, 1.996(3)Å]. The cadmium complex (2) is best described in terms of a polymer with the repeating unit consisting of two different centres, one seven, the other six-coordinate. With the first, the distorted MO₆S coordination sphere has four oxygens from two asymmetric bidentate car☐ylate groups (ligands B and C) [CdO, 2.36, 2.56(1)Å; 2.26, 2.67(1)Å], an oxygen and a sulphur from a bidentate chelate ligand (A) [CdO, 2.36(1)Å; CdS, 2.773(4)Å] and an oxygen from a bridging car☐yl group (ligand D) [CdO, 2.28(1)Å]. Ligands C and D also bridge two Cd centres through sulphurs [CdS, 2.739, 2.723(4)Å]. The second car☐yl oxygen of ligand A also forms a bridge to the second Cd [(CdO, 2.30(1)Å], while the distorted octahedral MO₄S₂ stereochemistry is completed by two waters [CdO, 2.25(1), 2.49(1)Å] and a sulphur from ligand D [CdS, 2.723(4)Å] giving a polymer structure. Complexes (3) and (4) are centrosymmetric tetra-car☐ylate bridged dimers [for (3) Cu ··· Cu, 2.586(3)Å; mean CuO(equatorial), 1.957(11)Å; for the two independent dimers in (4), Cu ··· Cu, 2.596(1), 2.616(1)Å; CuO (equatorial), 1.952(4), 1.968(4)Åmean]. The axial positions of the dimer in (3) are occupied by car☐yl oxygens of adjacent dimers [CuO, 2.280(9)Å] forming a polymer structure. In contrast, these positions in (4) are occupied by ethanol molecules with CuO, 2.222(3) and 2.177(4)Årespectively for the two independent dimers.     

A scaling theoretical analysis of vibrational relaxation experiments: rotational effects and long-range collisions

Expressions for the quantum number scaling of vibration—translation (VT) and vibration—vibration (VV) rates are derived. The derivation uses the recently developed scaling theory of non-reactive processes and invokes the assumption of rotational equilibrium. However, the VV and VT scaling relationships include rotational effects through the rotational energy gaps and the rotational distributions. The variables in this theory are a fundamental set of rates and the average collision range, l_c, for the particular inelastic process. The physically transparent meaning of these variables, combined with the a priori nature of the scaling coefficients, allows one to investigate actual dynamical effects and not just merely fit data. A detailed analysis of VV energy transfer in the COCO system is presented. Three conclusions are drawn: (1) rotational effects are crucially important in the scaling of the rates; (2) the process is predominantly long-range with l_c = 5.5 ± 0.5 au; and, (3) the available experimental data is consistent with single quanta vibrational changes in the VV rates.     

Reduction of chromano–piperidine-fused isoxazolidines: Tandem intramolecular rearrangements leading to 2-(methylamino)-4-oxo-N-phenyl-N-propyl-4H-chromene-3-carboxamide

Reductive ring opening of isoxazolidine moiety of chromano–piperidine-fused isoxazolidines (3a–c) with HCOONH₄ and 10% Pd/C in a mixture of solvents (THF/MeOH) at ambient temperature, affords novel 2-(methylamino)-4-oxo-N-phenyl-N-propyl-4H-chromene-3-carboxamide (4), which is apparently derived from reductive NO bond cleavage followed by tandem intramolecular rearrangements. Plausible mechanistic rationale for the formation of compound 4 is proffered.     

1,1-Bis(trifluoromethyl)butadiene-1,3—A new fluorinated building block

Although 1,1-bis(trifluoromethyl)butadiene-1,3 (1) reacts with dimethylamine with selective formation of 1,4-adduct [trans-(CF₃)₂CHCHCHCH₂N(CH₃)₂], halogenation of 1 proceeds with predominant formation (>92%) of 1,2-adducts (CF₃)₂CCHCHXCH₂X (X = Cl or Br). Electrophilic conjugated addition of “ClF” or “BrF” to 1 proceeds exclusively with the formation of 1,2-adducts (CF₃)₂CCHCHFCH₂X (major) and (CF₃)₂CCHCHXCH₂F (X = Cl or Br). Difluorocarbene adds selectively to CHCH₂ moiety of 1 forming thermally stable vinylcyclopropane. In Diels-Alder reaction with linear or cyclic dienes (butadienes, cyclopentadiene, cyclohexadiene-1,3) and quadricyclane compound 1 behaves as dienophile providing for the reaction electron-deficient CHCH₂ bond. The relative rate of cycloaddition of 1 and other fluoroolefins to quadricyclane, measured by high temperature NMR, indicates that (CF₃)₂CCH acts as very strong electron-withdrawing substituent. Synthetic utility of products based on 1 was also demonstrated.     

The Crystal and Molecular Structure of Bis(cyclopentadienyldicarbonylchromium) (CrCr)

The crystal structure of bis(cyclopentadienyldicarbonyl-chromium) has been determined by x-ray diffraction. The compound crystalizes in the triclinic system, space group P1¯(C¹_i, No. 2) with unit cell parameters: a, 7.829(3); b, 14.543(6); c, 6.588(2)Å; α, 94.67(3), β, 110.70(3); γ, 104.04°(3); V, 699.1(4)ų; z=2. There are two independent molecules per unit cell located at the inversion centers at O,O,O and O, 1/2, O. The CrCr bond distances are, respectively 2.200(3) and 2.230(3), thus supporting their formulation as triple bonds. The CpCrCr angles in the two molecules are 165.0° and 158.7°, respectively. The structural features are compared with those of Cp₂Mo₂(CO)₄, which has a linear CpMoMoCp axis; and the differences rationalized in terms of electronic interactions of the Cp-ligand with the orbitals of the M₂ unit. The differences observed in the structures of the two independent molecules are also related to the proposed bonding model and to packing considerations.     

Acetylene diethers: Dineopentyloxyethyne

Dineopentyloxyethyne has been synthesized fromtrans-2,3-dichloro-1,4-dioxane according to a general procedure already described. In contrast with alkyl neopentyloxyacetylenes, RC=COCH₂Bu^t, which only polymerize when are strongly heated (150°), dineopentyloxyethyne is a kinetically unstable acetylene diether that polymerizes readily at room temperature. However, the compound has been trapped with Co₂(CO)₈ to give either the corresponding hexacarbonyl complex, m.p. 74–75°, or the cyclic trimer, m.p. 205–206°, depending upon the experimental conditions.     

Palladium-catalyzed annulation of 2-(aryldiazenyl) aniline with dimethyl sulfoxide to access N-aryl-1H-benzo[d]imidazol-1-amine

A palladium-catalyzed annulation of 2-(aryldiazenyl) aniline and dimethyl sulfoxide was developed to access N-aryl-1H-benzo[d]imidazol-1-amine in moderate to good yields. Activated by 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) adduct (DABSO), DMSO served as a “CH” fragment during this procedure. It represents a facile pathway leading to benzimidazoles.     

Palladium-catalyzed acetoxylation of arenes by 1,2,3-triazole-directed CH activation

A facile and efficient method for the regioselective acetoxylation of 1,4-disubstituted 1,2,3-triazoles via Pd-catalyzed C$\text{<mglyph src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"></mglyph>}$H bond activation was developed. The cheap acetic acid was applied as the acetoxyl source to convert aromatic sp² C$\text{<mglyph src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"></mglyph>}$H bonds into C$\text{<mglyph src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"></mglyph>}$O bonds in high regioselectivity, employing 1,2,3-triazole as an elegant directing group and K₂S₂O₈ as the oxidant. A range of 1,2,3-triazoles bearing acetoxyl group can be synthesized with the reaction facilely.     

A theoretical study on the alkene insertion step in Rh-Yanphos catalyzed hydroformylation

This paper studied the mechanism of the alkene insertion elementary step in the asymmetric hydroformylation （AHF） catalyzed by RhH（CO）2[（R,S）-Yanphos] using four alkene substrates （CH2=CH- Ph, CH2=CH-Ph-（p）-Me, CH2=CH-C（==O）OCH3 and CH2=CH-OC（=O）-Ph, abbreviated as A1-A4）. Interestingly, the equatorial vertical coordination mode （A mode） with respect to the Rh center was found for AI and A2 but not for A3 and A4, although the equatorial in-plane coordination mode （E mode） was found for A1 -A4. The relative energy of the E mode of the -q2-intermediates is lower than that of the A mode. In the alkene insertion step, Path 1 is more favorable than Path 2 for this system. As for AI and A2, there could be a transformation between 2eq and 2ax.     

Nucleophilic substitution of 4-bromomethyltriazolium with different nucleophiles

1,2,3-Triazolium salts draw much attentions in recent years. We developed a new synthetic method to heteroatom-functionalized triazoliums via nucleophilic substitution of 4-bromomethyltriazolium. This method afforded triazoliums with different S, N, and O heteroatom-substituents. Moreover, S_N2′ reaction was observed with alcohols or hydroxides. In addition, debromination and debromomethylation reaction occurred in some cases.