A Conjugate Addition Approach to Diazo-Containing Scaffolds with β Quaternary Centers

Structurally complex diazo-containing scaffolds are formed by conjugate addition to vinyl diazonium salts. The electrophile, a little studied α-diazonium-α,β-unsaturated carbonyl compound, is formed at low temperature under mild conditions by treating β-hydroxy-α-diazo carbonyls with Sc(OTf)₃. Conjugate addition occurs selectively at the 3-position of indole to give α-diazo-β-indole carbonyls, and enoxy silanes react to give 2-diazo-1,4-dicarbonyl products. These reactions result in the formation of tertiary and quaternary centers, and give products that would be otherwise difficult to form. Importantly, the diazo functional group is retained within the molecule for future manipulation. Treating an α-diazo ester indole addition product with Rh₂(OAc)₄ caused a rearrangement to occur to give a 2-(1H-indol-3-yl)-2-enoate. In the case of diazo ketone compounds, this shift occurred spontaneously on prolonged exposure to the Lewis acidic reaction conditions.     

(NHC)NiH-Catalyzed Intermolecular Regio- and Diastereoselective Cross-Hydroalkenylation of Endocyclic Dienes with α-Olefins

Highly selective cross-hydroalkenylations of endocyclic 1,3-dienes at the least substituted site with α-olefins were achieved with a set of neutral (NHC)Ni^IIH(OTf) catalysts and cationic Ni^II catalysts with a novel NHC ligand. Under heteroatom assistance, skipped dienes were obtained in good yields, often from equal amounts of the two substrates and at a catalyst loading of 2–5 mol %. Rare 4,3-product selectivity (i.e., with the H atom at C4 and the alkenyl group at C3 of the diene) was observed, which is different from the selectivity of known dimerizations of α-olefins with both acyclic Co and Fe systems. The influence of the various substituents on the NHC, 1,3-diene, and α-olefin on the chemo-, regio-, and diastereoselectivity was studied. High levels of chirality transfer were observed with chiral cyclohexadiene derivatives.     

Diastereoselective Total Synthesis of the Euphorbia Diterpenoid Pepluanol A: A Reductive Annulation Approach

A new titanium(III)-catalyzed reductive annulation constructed a series of diversely functionalized 1,5-diols in good to excellent yields with respect to a wide scope of vinyl epoxide-aldehyde substrates. Taken together with a Diels–Alder reaction and a substrate-controlled diastereoselective cyclopropanation as additional key steps, the synthetic utility of this novel method has been preliminarily explored by the first and concise total synthesis of the Euphorbia diterpenoid (±)-pepluanol A.     

Catalytic Homologation-Allylboration Sequence for Diastereo- and Enantioselective Synthesis of Densely Functionalized β-Fluorohydrins with Tertiary Fluoride Stereocenters

Homologation of trisubstituted fluoroalkenes followed by allylboration of aldehyde, ketone and imine substrates is suitable for synthesis of β-fluorohydrin and amine products. In the presence of (R)-iodo-BINOL catalyst enantioselectivities up to 99 % can be achieved by formation of a single stereoisomer with adjacent stereocenters, of which one is a tertiary C−F center.     

Preparation and Characterization of A New Dinuclear Ruthenium Complex with BDPX Ligand and Its Catalytic Hydrogenation Reactions for Cinnamaldehyde

Introduction Recently, dinuclear Ru complexes containing chelating bidentate phosphines (either chiral or non-chiral) have attracted more and more attention owing to their effective ability for catalytic hydrogenation of olefins and carbonyl groups under mild conditions. A great number of dinuclear Ru complexes with bidentate phosphines have been obtained.1-10 In 1985 Ikariya et al.1 prepared a chiral binuclear ruthenium complex [Ru2Cl4(BINAP)2]NEt3 by the reaction of (S)-BINAP with [R…     

Regio- and Diastereoselective Synthesis of Cyclohexadienylborons via an Intermolecular Diels–Alder Reaction of Alkenyl MIDA Boronates with 2-Pyrones

An efficient synthesis of highly functionalized cyclohexadienylborons via an inverse electron-demand Diels–Alder reaction/CO₂ extrusion of alkenyl MIDA boronates with 2-pyrones is outlined. By controlling the reaction temperature, the corresponding C(sp³)-rich bicyclolactones could also be readily formed. The exo-selective reactions feature good functional-group tolerance, broad substrate scope, and excellent regio- and diastereoselectivity. Oxidation of the cyclohexadienylborons in a one-pot procedure led to the construction of aromatic boronates bearing valuable functional groups. Synthetic transformations of the C−B bond were demonstrated.     

Catalytic Membranes and Membrane Reactors： An Integrated Approach to Catalytic Process with a High Efficiency and a Low Environmental Impact

The design of new heterogeneous photooxygenation systems able to employ visible light,oxygen,mild temperatures,and solvent with a low environmental impact has been investigated. In particular,the heterogenization of decatungstate (W10O4-32),a polyoxometalate with photocatalytic activity in oxidation reactions,has been carried out in polymeric membranes of polyvinylidenefluoride. The polymeric catalytic membranes prepared by phase inversion technique have been successfully applied in the aerobic mineralization of phenol in water,which was used as an example of organic pollutant. In order to evaluate the effect of the polymeric environment on the overall catalyst behavior,we have also heterogenized the decatungstate (opportunely functionalized) in perfluorinated membrane made of Hyflon. The photocatalytic composite membranes are characterized by different and tuneable properties depending on the nature of the polymeric micro-environment,in which the catalyst is confined. Moreover,the selective separation function of the membrane results in enhanced performance in comparison with homogeneous reactions.     

2 + 2 Dimerization of cinnamylidene malonic acid: A structural and kinetic study

Cinnamylidene malonic acid was synthesized and its crystal structure obtained. The dicarboxylic acid hydrogen-bonding motif of this structure consists of catemer chains that lie along the c- glide plane. A photo induced 2?+?2 cycloaddition occurred upon exposure of the crystals to UV light which resulted in the destruction of the crystal. The structure of the photo products were determined by IR and NMR analysis. The regio- and stereo-chemistry of the photoproduct can be rationalized by examining the relative orientation and symmetry relating reacting molecules within the crystal structure. A kinetic study demonstrated first order reaction kinetics which is consistent with a reaction occurring under topochemical control.     

Amines as Catalysts: Dynamic Features and Kinetic Control of Catalytic Asymmetric Chemical Transformations to Form C−C Bonds and Complex Molecules

Carbonyl transformations involving enolates and/or enamines have been used for various types of bond-forming reactions. In this account, catalysts and catalyst systems that have amino acids or primary, secondary, and/or tertiary amines as key catalytic functional groups that we have developed to accelerate chemical transformations, including regio-, diastereo- and enantioselective reactions, are discussed. Our chemical transformation strategies and methods that use amine derivatives as catalysts are also discussed. As amines can have different functions depending on protonation and on the species formed during the catalysis (such as enamines and iminium ions), dynamics and kinetic controls are the keys for understanding the catalysis. Further, strategies that harness dynamic steps and kinetic control in amine-catalyzed reactions have enabled the synthesis of complex molecules in stereocontrolled manners. Understanding the dynamic features and the kinetic controls of the catalysis will further the design of the catalysts and the development of chemical transformation strategies and methods.     

Synthesis of Acyclic Aliphatic Amides with Contiguous Stereogenic Centers via Palladium-Catalyzed Enantio-, Chemo- and Diastereoselective Methylene C(sp3)−H arylation

The enantioselective desymmetrizing C−H activation of α-gem-dialkyl acyclic amides remains challenging because the availability of four chemically identical unbiased methylene C(sp³)−H bonds and increased rotational freedoms of the acyclic systems add tremendous difficulties for chemo- and stereocontrol. We have developed a method for the synthesis of acyclic aliphatic amides with α,β-contiguous stereogenic centers via Pd^II-catalyzed asymmetric arylation of unbiased methylene C(sp³)−H, in good yields and with high levels of enantio-, chemo- and diastereoselectivity (up to >99 % ee and >20:1 d.r.). Successive application of this method enables the sequential arylation of the gem-dialkyl groups with two different aryl iodides, giving a range of β-Ar¹-β′-Ar²-aliphatic acyclic amides containing three contiguous stereogenic centers with excellent diastereoselectivity.     

The Reaction of Phosphoryl Chlorides with Enamines - A New Approach to β-Ketophosphonates

Abstract

Several approaches are available for the preparation of β-ketophosphonate esters. A Michaelis-Arbuzov approach using the reaction of an α-halo ketone with a trialkyl phosphite may in certain instances be controlled to favor the preparation of the target materials. However, an alternative pathway leading to the formation of vinyl phosphate esters often predominates. (This reaction system has recently been reviewed by Borowitz and Borowitz.¹) An alternative approach is that developed in recent years by Wiemer, et al.² involving the rearrangement of vinyl phosphate esters to the β-ketophosphonates.     

Reaction of 1-Iodoalkynes with Tin Metal: A New Approach to the Sn–Csp Bond Formation

Russian Journal of General Chemistry - Tin iodoalkynylides were synthesized by the reaction of 1-iodoalkynes with tin metal. The scope of the reaction and the composition of the resulting mixtures...     

Synthesis,Crystal Structure and Magnetic Behavior of a Novel Cd(Ⅱ) Complex with Four Nitroxide Radicals

A novel diamagnetic-metal Cd(Ⅱ) complex with four nitroxide radicals[Cd(IM4Py)4Cl2](IM4Py=2-(4'-pyridinyl)-4,4,5,5-tetramethylimidazoline-1-oxyl) was synthesized and characterized by elemental analyses,IR spectra,UV-Vis spectra and X-ray single crystal diffraction.The complex crystallized in triclinic space group P1 with a=0.93285(14) nm,b=1.16827(18) nm,c=1.3660(2) nm,α=112.759(2)°,β=104.524(2)°,γ=92.008(3)°,V= 1.3143(3) nm3,Z=1,Dc=1.335 g/cm3,the final R1=0.0423 and wR2=0.1009.In the title complex,each Cd(Ⅱ) ion adopting a distorted octahedral geometry is coordinated by two Cl-anions and four pyridyl-N atoms from four IM4Py ligands.The magnetic measurements show the weak antiferromagnetic interactions between the nitroxide radicals.     

A Silver Complex of 6,7-Dicyanodipyridoquinoxaline: π-Stacking Interactions and Luminescence

The reaction of 6,7-dicyanodipyridoquinoxaline (DICNQ) with AgNO3 in a 1:1 molar ratio by solution method gave a new complex [Ag(DICNQ)2]NO3 1. Single-crystal X-ray diffraction analysis reveals that the complex crystallizes in the space group Ibca of orthorhombic system with eight formula units in a cell. Crystal data for 1: a = 15.7055(17), b = 18.411(2), c = 20.680(2) (A), V = 5979.7(11) (A)3, Z = 8, C32H12AgN13O3, Mr = 734.42, Dc = 1.632 g/cm3, (μ = 0.734 mm-1, F(000) = 2928, S = 1.023 and T = 293(2) K. The final R = 0.0659 and wR = 0.1927 for 2118 observed reflections with I > 2σ(I), and R = 0.0801 and wR = 0.2196 for all data. The complex builds up a packing structure by π-π stacking interactions and shows a luminescent feature.     

Direct Catalytic Conversion of Ethanol to C5+ Ketones: Role of Pd–Zn Alloy on Catalytic Activity and Stability

Ethanol can be used as a platform molecule for synthesizing valuable chemicals and fuel precursors. Direct synthesis of C₅₊ ketones, building blocks for lubricants and hydrocarbon fuels, from ethanol was achieved over a stable Pd-promoted ZnO-ZrO₂ catalyst. The sequence of reaction steps involved in the C₅₊ ketone formation from ethanol was determined. The key reaction steps were found to be the in situ generation of the acetone intermediate and the cross-aldol condensation between the reaction intermediates acetaldehyde and acetone. The formation of a Pd–Zn alloy in situ was identified to be the critical factor in maintaining high yield to the C₅₊ ketones and the stability of the catalyst. A yield of >70 % to C₅₊ ketones was achieved over a 0.1 % Pd-ZnO-ZrO₂ mixed oxide catalyst, and the catalyst was demonstrated to be stable beyond 2000 hours on stream without any catalyst deactivation.     

Synthesis,Crystal Structure and Magnetic Property of a New Cd（Ⅱ） Complex with Four Nitronyl Nitroxide Radicals

A new Cd(Ⅱ) complex with four nitronyl nitroxide radicals [Cd(NIT4Py)4Cl2](NIT4Py = 2-(4'-pyridinyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) has been synthesized and structurally characterized by X-ray diffraction analysis.It crystallizes in triclinic,space group P1 with a = 7.2441(4),b = 13.6964(8),c = 13.7354(8) ,α = 89.8610(10),β = 77.9180(10),γ = 87.2250(10)°,V = 1331.01(13) 3,C48H64CdCl2N12O8,Mr = 1120.41,Z = 1,Dc = 1.398 g/cm3,μ(MoKα) = 0.573 mm-1,F(000) = 582,S = 1.043,the final R = 0.0257 and wR = 0.0641 for 4333 observed reflections(I > 2σ(I)).The title complex exists in the mononuclear-metal structures,in which each Cd(Ⅱ) ion adopts a distorted octahedral geometry and is coordinated by two Cl-anions and four pyridyl-N atoms from four NIT4Py ligands.The magnetic measurements show weak antiferromagnetic interactions between the nitroxide radicals.     

Asymmetric Inverse-Electron-Demand Hetero-Diels–Alder Reaction for the Construction of Bicyclic Skeletons with Multiple Stereocenters by Using a Bifunctional Organocatalytic Strategy: An Efficient Approach to Chiral Macrolides

We have performed the first bifunctional organocatalytic highly enantioselective inverse-electron-demand hetero-Diels–Alder reaction of cyclic ketones with enones to afford densely functionalized bicyclic skeletons that contain three stereocenters (up 82 % yield, 10:1 d.r., and 97 % ee). Unlike the previous IEDDAR catalytic strategy, this method features a double HOMO_dienophile/ LUMO_diene-activated pathway. Moreover, this process provides a promising method for the construction of enantioenriched macrolides.     

A Methane Monooxygenase－like DinuclearIron （Ⅲ） Complex and its Catalytic Ability for Asymmetric Epoxidation of Styrene

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