钌1,2-萘醌-1-肟配合物对aldol C—C成键反应的催化作用

在钌1,2-萘醌-1-肟(1-nqo)配合物cis,cis-[Ru(1-nqo)₂(CO)(NCMe)] (1)或trans,trans-[Ru(1-nqo)₂(PBu₃)₂] (2)的作用下, 氰基乙酸乙酯与取代苯甲醛发生aldol C—C成键反应. 根据GC-MS检测及HPLC分离结果, 对二苯甲醛的二个醛基可分别或同时与氰基乙酸乙酯发生aldol反应. ¹H NMR表征结果证明, 二种产物的双键构型均为反式. 其它取代苯甲醛的反应均给出单一反式aldol产物, 这表明该催化反应具有立体选择性. 配合物1的催化活性稍差, 产率不超过60%, 而配合物2的催化活性要高于1, 最高产率达99%.     

New saponins from Sechium mexicanum

The chemical study of Sechium mexicanum roots led to the isolation of the two new saponins {3‐O‐β‐D ‐glucopyranosyl (1 → 3)‐β‐D ‐glucopyranosyl‐2β,3β,16α,23‐tetrahydroxyolean‐12‐en‐28‐oic acid 28‐O‐α‐L ‐rhamnopyranosyl‐(1 → 3)‐β‐D ‐xylopyranosyl‐(1 → 4)‐α‐L ‐rhamnopyranosyl‐(1 → 2)‐α‐L ‐arabinopyranoside} (1) and {3‐O‐β‐D ‐glucopyranosyl (1 → 3)‐β‐D ‐glucopyranosyl‐2β,3β,16α,23‐tetrahydroxyolean‐12‐en‐28‐oic acid 28‐O‐α‐L ‐rhamnopyranosyl‐(1 → 3)‐β‐D ‐xylopyranosyl‐(1 → 4)‐[β‐D ‐apiosyl‐(1 → 3)]‐α‐L ‐rhamnopyranosyl‐(1 → 2)‐α‐L ‐arabinopyranoside} (2), together with the known compounds {3‐O‐β‐D ‐glucopyranosyl‐(1 → 3)‐β‐D ‐glucopyranosyl‐2β,3β,6β,16α,23‐pentahydroxyolean‐12‐en‐28‐oic acid 28‐O‐α‐L ‐rhamnopyranosyl‐(1 → 3)‐β‐D ‐xylopyranosyl‐(1 → 4)‐α‐L ‐rhamnopyranosyl‐(1 → 2)‐α‐L ‐arabinopyranoside} (3), tacacosides A₁ (4) and B₃ (5). The structures of saponins 1 and 2 were elucidated using a combination of ¹H and ¹³C 1D‐NMR, COSY, TOCSY, gHMBC and gHSQC 2D‐NMR, and FABMS of the natural compounds and their peracetylated derivates, as well as by chemical degradation. Compounds 1–3 are the first examples of saponins containing polygalacic and 16‐hydroxyprotobasic acids found in the genus Sechium, while 4 and 5, which had been characterized partially by NMR, are now characterized in detail. Copyright © 2009 John Wiley & Sons, Ltd.     

Redox-Induced Oxidative C−C Bond Cleavage of 2,2′-Pyridil in Diruthenium Complexes

In the recent years, there has been an emerging research interest in the domain of C−C bond-cleavage reactions. The present contribution deals with the redox-mediated dioxygen activation and C−C bond cleavage in a diruthenium complex [(acac)₂Ru^II(μ-L1)Ru^II(acac)₂], 1 (acac=acetylacetonate) incorporating 2,2′-pyridil (L1) as the bridging ligand. The above process leads to a C−C-cleaved monomeric product [(acac)₂Ru^III(pic⁻)], 2 (pic⁻=piconilate). Intriguingly, similar diastereomeric complexes [(acac)₂Ru^II(μ-L2)Ru^II(acac)₂], meso (ΔΛ): 3 a and rac (ΔΔ/ΛΛ): 3 b , involving an analogous diimine bridge (L2=N1,N2-diphenyl-1,2-di(pyridin-2-yl)ethane-1,2-diimine), were stable towards such oxidative transformations. Electrochemical and spectroelectrochemical studies, in combination, establish the potential non-innocent feature of the 2,2′-Pyridil (L1) and its derivative (L2) both in oxidation and reduction processes. Additionally, theoretical calculations have been employed to verify the redox states and their behavior. Furthermore, transition state (TS) calculations at the M06L/6-31G*/LANL2DZ level of theory together with detailed kinetic studies outline a putative mechanism for the selective transformation of 1 → 2 involving the formation of an intermediate bearing peroxide linkage to complex 1 .     

Are there reliable DFT approaches for 13C NMR chemical shift predictions of fullerene C60 derivatives?

The relationships between experimental and theoretical ¹³C NMR chemical shifts of a pristine fullerene C₆₀, monoadducts from [2 + n] cycloaddition (n = 1–3), and one [2 + 1] bis‐adduct are systematically analyzed for the first time by using diverse quantum‐chemical levels of theory. These levels involved B3LYP, B3PW91, B97‐2, mPW1PW91, PBE1PBE, and X3LYP hybrid functionals combined with 3‐21G, 6‐31G, 6‐31G(d), 6‐31G(d,p), 6‐31G(d,2p), LanL2DZ, and SDDAll basis sets. X3LYP/6‐31G approach is determined to have the lowest deviations from the ¹³C NMR experimental data compared to the other methods for all the fullerene compounds (mean absolute error value is 0.856 ppm and root mean squared error value is 1.197 ppm). The highest deviations are characteristic for α (sp² C2/C5/C8/C10) and β (sp² C6/C7/C11/C12) carbon atoms relative to a functionalization site and for those (sp³ C1/C9) directly attached with a side fragment in the [2 + n] monoadducts (n = 1–3). A probable reason of such deviation is that the approaches do not take into account a contribution of paramagnetic ring currents to ¹³C NMR chemical shifts. The results will be useful in design of novel fullerene derivatives and in performing unambiguous ¹³C NMR chemical shift assignments with modern quantum chemistry calculations.     

Oxidative Coordination versus C3−C(O)Me Bond Cleavage in Acetylacetonate Iridium Complexes

Iridabicycles [Ir{κ³-N,C,O-(pyC(H)=C(C(O)Me)₂}(Cl)(L−L)](L−L=cod (cod=1,5-cyclooctadiene), 1 a ; bipy (bipy=2,2’-bipyridine), 1 b ) have been obtained by oxidative coordination of 3-(pyridine-2-yl-methylene)pentane-2,4-dione L1 , to the complexes [{Ir(μ-Cl)(cod)}₂] and [{Ir(μ-Cl)(coe)₂}₂] (coe=cis-cyclooctene), the latter in the presence of bipy. Remarkably, cleavage of the C³−C(O)Me bond of L1 has instead been achieved in the reaction with [Ir(Cl)(dmb)₂] (dmb=2,3-dimethylbutadiene), yielding a compound formulated as [Ir{κ²-N,C-(pyC(H)C(C(O)Me))}(CO)(μ-Cl)(Me)]₂, 2 . Treatment of dimer 2 with DMSO or PMe₃ produced the complexes[Ir{κ²-N,C-(pyC(H)C(C(O)Me)}(CO)Cl(Me)L] (L=DMSO, 3 a ; PMe₃, 3 b ). Plausible mechanisms for the reactions leading to complexes 1 and 2 are proposed by means of DFT calculations.     

Front Cover: Small-Molecule Activation by Heteroleptic Metallasilylenes (Eur. J. Inorg. Chem. 2/2023)

We report on reactions of heteroleptic metallasilylenes L¹(Cl)MSiL² (M=Al 1 , Ga 2 , L¹=HC[C(Me)NDipp]₂, Dipp=2,6-ⁱPr₂C₆H₃; L²=PhC(N^tBu)₂) with CO₂, N₂O, and Me₃SiN₃, yielding the corresponding carbonate complexes L¹(Cl)MOSi(CO₃-κ²O,O−)L² (M=Al 3 , Ga 4 ), silanoic esters L¹(Cl)MOSi(O)L² (M=Al 5 , Ga 6 ), and silaimine L¹(Cl)GaSi(NSiMe₃)L² ( 8 ), whereas {L²Si[N(SiMe₃)Al(Cl)C(Me)NDipp][CHC(Me)N(Dipp)]} 7 was formed by C−C bond cleavage of the L¹ ligand. Compounds 3 – 8 were characterized by NMR (¹H, ¹³C) and IR spectroscopy, elemental analysis and single crystal X-ray diffraction.     

A New 18(13 → 12β)‐abeo‐Lanostadiene Triterpenoid from Ganoderma fornicatum

A new triterpenoid, fornicatin C (= (3β)‐3‐hydroxy‐18(13 → 12β)‐abeo‐lanosta‐13(17),24‐dien‐18‐oic acid; 1 ), was isolated from the fruiting bodies of Ganoderma fornicatum, together with the known compounds fornicatin A ( 2 ) and fornicatin B ( 3 ), among other constituents. The structure of 1 was elucidated by means of spectroscopic techniques, and those of 2 and 3 were identified by comparing their spectroscopic data with those reported in the literature.     

Triphenylphosphinopalladium(II) complexes with ONO‐donor ligands: syntheses,structures and catalytic applications in C?C cross‐coupling reactions

Reactions of 1‐((2‐hydroxy‐5‐R‐phenylimino)methyl)naphthalen‐2‐ols (H₂Lⁿ , n  = 1–3 for R = H, Me, Cl, respectively) with [Pd(PPh₃)₂Cl₂] and Et₃N in toluene under reflux produced three new mononuclear square‐planar palladium(II) complexes with the general formula [Pd(Lⁿ )(PPh₃)] ( 1 , R = H; 2 , R = Me; 3 , R = Cl). All the complexes were characterized using elemental analysis, solution conductivity and various spectroscopic (infrared, UV–visible and NMR) measurements. Molecular structures of 1 , 2 , 3 were confirmed using single‐crystal X‐ray diffraction analysis. In each complex, the fused 5,6‐membered chelate rings forming phenolate‐O, azomethine‐N and naphtholate‐O donor (Lⁿ )²⁻ and the PPh₃ form a square‐planar ONOP coordination environment around the metal centre. Infrared and NMR spectroscopic features of 1 , 2 , 3 are consistent with their molecular structures. Electronic spectra of the three complexes display several strong primarily ligand‐centred absorption bands in the range 322–476 nm. All the complexes were found to be effective catalysts for carbon–carbon cross‐coupling reactions of arylboronic acids with aromatic and heteroaromatic aldehydes to form the corresponding diaryl ketones. Copyright © 2016 John Wiley & Sons, Ltd.     

New synthetic approach to 8-allyltheophylline

Summary The synthesis of 8-allyltheophylline (8) from 5,6-diamino-1,3-dimethyluracil (1) and 3-butenoic acid byTraube's methodvia 6-amino-5-(3-butenoylamino)-1,3-dimethyluracil (2) failed because an attempted alkaline cyclization of the intermediate2 afforded (E)-8-(1-propenyl)-theophylline (3) under rearrangement of the terminal C=C bond. Therefore, the cyclodehydratation of 6-(3-butenylamino)-5-nitroso-1,3-dimethyluracil (7), available from 6-chloro-1,3-dimethyluracil (5)via 6-(3-butenylamino) derivative6 has to be used for obtaining the required product8.

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Ein neuer synthetischer Zugang zu 8-Allyltheophyllin

Zusammenfassung 8-Allyltheophyllin (8) kann nicht mittels derTraube-Synthese aus 5,6-Diamino-1,3-dimethyluracil und 3-Butensäurevia 6-Amino-5-(3-butenoylamino)-1,3-dimethyluracil (2) hergestellt werden, wei bei der alkalischen Cyclisierung des Zwischenproduktes2 Umlagerung der terminalen C=C-Doppelbindung unter Bildung von (E)-8-(1-Propenyl)theophyllin (3) erfolgt. Zur Darstellung der Verbindung8 muss man daher die Dehydratationscyclisierung von 6-(3-Butenylamino)-5-nitroso-1,3-dimethyluracil (7) anwenden. Letzteres ist aus 6-Chloro-1,3-dimethyluracil über das 6-(3-Butenylamino)-Derivat6 zugänglich.

     

Unexpected C–C Bond Formation with a Ferrocenyl Fischer Carbene Complex

Thermolysis of (OC)₅Cr(C(OEt)(Fc)) ( 1 ) gives 2,N-diferrocenyl acetamide Fc–CH₂–CO–NH–Fc ( 2 ) in the presence of amino ferrocene Fc-NH₂. In the absence of a nucleophile, 4-ethoxy-2,3,4-triferrocenyl-cyclobut-2-enone ( 3 ) forms from 1 under thermal activation. Single crystal X-ray diffraction, NMR spectroscopy and mass spectrometry unambiguously confirm the structure of both unexpected products. Quantum chemical calculations and kinetic experiments by mass spectrometry and IR spectroscopy help to propose conceivable pathways to their formation.     

Divergent Carbocatalytic Routes in Oxidative Coupling of Benzofused Heteroaryl Dimers: A Mechanistic Update

Mildly thermal air or HNO₃ oxidized activated carbons catalyse oxidative dehydrogenative couplings of benzo[b]fused heteroaryl 2,2’-dimers, e.g., 2-(benzofuran-2-yl)-1H-indole, to chiral 3,3’-coupled cyclooctatetraenes or carbazole-type migrative products under O₂ atmosphere. DFT calculations show that the radical cation and the Scholl-type arenium cation mechanisms lead to different products with 2-(benzofuran-2-yl)-1H-indole, being in accord with experimental product distributions.     

Two New Steroidal Saponins from the Fresh Leaves of Agave sisalana

A new furostanol saponin, sisalasaponin C ( 1 ), and a new spirostanol saponin, sisalasaponin D ( 2 ), were isolated from the fresh leaves of Agave sisalana, along with three other known steroidal saponins and two stilbenes. Their structures were identified as (3β,5α,6α,22α,25R)‐3,26‐bis[(β‐D ‐glucopyrano‐ syl)oxy]‐22‐hydroxyfurostan‐6‐yl β‐D ‐glucopyranoside ( 1 ), (3β,5α,25R)‐12‐oxospirostan‐3‐yl 6‐deoxy‐α‐L ‐mannopyranosyl‐(1→4)‐β‐D ‐glucopyranosyl‐(1→3)‐[β‐D ‐xylopyranosyl‐(1→3)‐β‐D ‐glucopyranosyl‐(1→2)]‐β‐D ‐glucopyranosyl‐(1→4)‐β‐D ‐galactopyranoside ( 2 ), (3β,5α,6α,22α,25R)‐22‐methoxyfurostane‐3,6,26‐triyl tris‐β‐D ‐glucopyranoside, cantalasaponin‐1, polianthoside D, (E)‐ and (Z)‐2,3,4′,5‐tetrahydroxystilbene 2‐O‐β‐D ‐glucopyranosides. The last three known compounds were isolated from the fresh leaves of Agavaceae for the first time. The structures of the new compounds were elucidated by detailed spectroscopic analysis, including 1D‐ and 2D‐NMR experiments, and chemical techniques.     

Two New Sesquiterpenes from the Roots of Valeriana fauriei Briq.

A phytochemical investigation of the MeOH extract of Valeriana fauriei Briq . roots resulted in the isolation of two new sesquiterpenes, isovalerianin A (=(1β,4Z,6β,8α)‐8‐(acetyloxy)‐1,10‐dihydroxy‐6,11‐cyclogermacr‐4‐en‐15‐al=rel‐(1R,2Z,6S,7R,9R,10S)‐9‐(acetyloxy)‐6,7‐dihydroxy‐7,11,11‐trimethylbicyclo[8.1.0]undec‐2‐ene‐3‐carboxaldehyde; 1 ) and valerianin C (=(2α,3α,6α,8α)‐3‐(acetyloxy)‐2,4,8‐trihydroxyguai‐1(10)‐ene‐12,6‐lactone=rel‐(3R,3aS,4R,7S,8S,9R,9aR,9bR)‐8‐(acetyloxy)‐3a,4,5,7,8,9,9a,9b‐ octahydro‐4,7,9‐trihydroxy‐3,6,9‐trimethylazuleno[4,5‐b]furan‐2(3H)‐one; 2 ), together with six known compounds, i.e., camphor, methyl 4‐hydroxybenzoate, 2‐methoxybenzoic acid, benzoic acid, quercetin, and kaempferol. The structures of the compounds were established by detailed spectral analysis and comparison with previously reported data.     

Intramolecular C?H Activation through Gold(I)‐Catalyzed Reaction of Iodoalkynes

The cycloisomerization reaction of 1‐(iodoethynyl)‐2‐(1‐methoxyalkyl)arenes and related 2‐alkyl‐substituted derivatives gives the corresponding 3‐iodo‐1‐substituted‐1H‐indene under the catalytic influence of IPrAuNTf₂ [IPr=1,3‐bis(2,6‐diisopropyl)phenylimidazol‐2‐ylidene; NTf₂=bis(trifluoromethanesulfonyl)imidate]. The reaction takes place in 1,2‐dichloroethane at 80 °C, and the addition of ttbp (2,4,6‐tri‐tert‐butylpyrimidine) is beneficial to accomplish this new transformation in high yield. The overall reaction implies initial assembly of an intermediate gold vinylidene upon alkyne activation by gold(I) and a 1,2‐iodine‐shift. Deuterium labeling and crossover experiments, the magnitude of the recorded kinetic primary isotopic effect, and the results obtained from the reaction of selected stereochemical probes strongly provide support for concerted insertion of the benzylic C H bond into gold vinylidene as the step responsible for the formation of the new carbon–carbon bond.     

Structure elucidation of four prenylindole derivatives from Streptomyces sp. isolated from Ailuropoda melanoleuca feces

Four new prenylindole derivatives, (R)‐6‐(2,3‐dihydroxy‐3‐methylbutyl)indole (1), (R)‐6‐(2,3‐dihydroxy‐3‐methylbutyl)indolin‐2‐one (2), and an unseparated mixture of (Z)‐6‐(4‐hydroxy‐3‐methylbut‐2‐en‐1‐yl)indolin‐2‐one (3a) and (E)‐6‐(4‐hydroxy‐3‐methylbut‐2‐en‐1‐yl)indolin‐2‐one (3b) with a ratio of 3 : 2, were isolated from the culture broth of a streptomycete isolated from Ailuropoda melanoleuca feces. Their structures were elucidated on the basis of 1D and 2D NMR spectroscopic techniques. The absolute configuration of 1 was determined by Mosher's method. Copyright © 2013 John Wiley & Sons, Ltd.     

Three New Phthalides from Gnaphalium adnatum

Three new phthalides, gnaphalides A–C ( 1 – 3 , resp.), together with three known phthalides, were isolated from the aerial part of Gnaphalium adnatum. The structures of the new compounds were elucidated as 6‐(1,1‐dimethylprop‐2‐en‐1‐yl)‐5,7‐dihydroxy‐2‐benzofuran‐1(3H)‐one ( 1 ), 5‐hydroxy‐7‐[(2‐hydroxy‐3‐methylbut‐3‐en‐1‐yl)oxy]‐2‐benzofuran‐1(3H)‐one ( 2 ), and 1,3‐dihydro‐7‐[(3‐methylbut‐2‐en‐1‐yl)oxy]‐1‐oxo‐2‐benzofuran‐5‐yl β‐D ‐glucopyranoside ( 3 ) on the basis of spectral analyses. The structure of 1 was also confirmed by X‐ray crystallographic analysis. The three known phthalides, identified as 5,7‐dihydroxyisobenzofuran‐1(3H)‐one ( 4 ), anaphatol ( 5 ), and 7‐O‐(β‐glucopyranosyl)‐5‐hydroxyisobenzofuran‐1(3H)‐one ( 6 ), were isolated from the genus Gnaphalium for the first time.     

Triterpenoid Constituents of Huperzia miyoshiana

Thirteen triterpenoids, including three new ones, miyoshianois A (1), B (2) and C (3), were isolated from Huperzia miyoshiana. The structures of these new compounds were established as 3-O-dihydroferuloyltohogenol (1), 16-oxo-3β,21β-dihydrox-y-serrat-14-en-24-ferulate (2) and 16-oxo-3a, 21β-dihydroxy-serrat-14-en-24-ferulate (3), respectively, on the basis of their spectroscopic analysis.     

Synthese und Molekülstrukturen von N‐substituierten Diethylgallium‐2‐pyridylmethylamiden

Synthesis and Molekular Structures of N‐substituted Diethylgallium‐2‐pyridylmethylamides (2‐Pyridylmethyl)(tert‐butyldimethylsilyl)amine ( 1a ) and (2‐pyridylmethyl)‐di(tert‐butyl)silylamine ( 1b ) form with triethylgallane the corresponding red adducts 2a and 2b via an additional nitrogen‐gallium bond. These oily compounds decompose during distillation. Heating under reflux in toluene leads to the elimination of ethane and the formation of the red oils of [(2‐pyridylmethyl)(tert‐butyldimethylsilyl)amido]diethylgallane ( 3a ) and [(2‐pyridylmethyl)‐di(tert‐butyl)silylamido]diethylgallane ( 3b ). In order to investigate the thermal stability solvent‐free 3a is heated up to 400 °C. The elimination of ethane is observed again and the C‐C coupling product N, N′‐Bis(diethylgallyl)‐1, 2‐dipyridyl‐1, 2‐bis(tert‐butyldimethylsilyl)amido]ethan ( 4 ) is found in the residue. Substitution of the silyl substituents by another 2‐pyridylmethyl group and the reaction of this bis(2‐pyridylmethyl)amine with GaEt₃ yield triethylgallane‐diethylgallium‐bis(2‐pyridylmethyl)amide ( 5 ). The metalation product adds immediately another equivalent of triethylgallane regardless of the stoichiometry. The reaction of GaEt₃ with 2‐pyridylmethanol gives quantitatively colorless 2‐pyridylmethanolato diethylgallane ( 6 ).     

The Crystal Structures of Trimethylphosphane supported Nickel‐ and Cobalt‐Methyl Complexes: Octahedral mer‐cis‐[CoIIII(CH3)2(PMe3)3] and Square Planar trans‐[NiIICl(CH3)(PMe3)2]

Single crystals of octahedral mer‐cis‐[Co^IIII(CH₃)₂(PMe₃)₃] ( 1 ) and square planar trans‐[Ni^IICl(CH₃)(PMe₃)₂] ( 2 ), were obtained from solvent mixtures (methylcylohexane / pentane 1:1) and have been analyzed by X‐ray crystallography for the first time.     

Raman and Infrared Spectra for All-trans-astaxanthin in Dimethyl Sulfoxide Solvent

The Raman and infrared spectra of all-trans-astaxanthin (AXT) in dimethyl sulfoxide (DMSO) solvent were investigated experimentally and theoretically. Density functional cal-culations of the Raman spectra predict the splitting of the υ₁ band into υ_1-1 and υ_1-2 compo-nents. The absence of splitting in Raman experimental spectra is ascribed to the competition between the two symmetric C=C stretching vibrations of the backbone chain. The υ₁ band is very sensitive to the excitation wavelength: resonance excitation stimulates the higher-frequency υ_1-2 mode, and off-resonance excitation corresponds to the lower-frequency υ_1-1 mode. Analyses of the intramolecular hydrogen bonding between C=O and O-H in the AXT/DMSO system reveal that the C4=O1...H1-O3 and C4'=O2...H2-O4 bonds are strengthened and weakened, respectively, in the electronically excited state compared with those in the ground state. This result reveals significant variations of the AXT molecular structure in different electronic states.