Xinquan Hu

Synthesis, characterisation and ethylene oligomerization behaviour of N -(2-substituted-5,6,7-trihydroquinolin-8-ylidene)arylaminonickel dichlorides

A series of N-(2-substituted-5,6,7-trihydroquinolin-8-ylidene)-arylaminonickel(II) dichlorides were synthesized by the one-pot stoichiometric reaction of nickel dichloride, 2-chloro- or 2-phenyl-substituted 5,6,7-trihydroquinolin-8-one, and the corresponding anilines. All nickel complexes were characterized by elemental and spectroscopic analysis. The molecular structures of representative nickel complexes, determined by the single-crystal X-ray diffraction, indicate the different coordination numbers around nickel either four with more bulky ligands or five with less bulky ligands. All nickel complexes, activated with ethylaluminium sesquichloride (Et3Al2Cl3), showed high activities (up to 9.5 × 106 g mol−1 h−1) in ethylene oligomerization for dimer and trimers.

Diastereo‐ and Enantioselective Catalytic Tandem Michael Addition/Mannich Reaction: Access to Chiral Isoindolinones and Azetidines with Multiple Stereocenters

Construction of multiple contiguous stereogenic centers in acyclic compounds by asymmetric catalysis represents a particularly difficult challenge. For the success of such a catalytic process, carbon–carbon bond-forming tandem reactions using well-known reactions as key transformation steps that give high diastereoand enantiocontrol are a prerequisite. The asymmetric Mannich-type reaction is a popular method for preparing optically active b-aminocarbonyl frameworks, which are interesting structures found in many useful biologically active compounds. This type of reaction has been frequently used as a fundamental step for establishing tandem protocols, and in those processes, the catalytic generation of chiral enolates is crucial for achieving high activity and selectivity. It is widely appreciated that copper-catalyzed conjugate addition of R2Zn to a,b-unsaturated carbonyl compounds is one of the most attractive way for constructing a carbon– carbon bond, in which the chiral zinc enolate is generated in situ. In the case when an appropriate electrophile is added to the reaction system, the tandem conjugate addition/ electrophilic trapping reaction might be realized. Based on this concept, various electrophiles such as aldehydes, ketones, esters, nitriles, oxocarbenium ions, carboxylates, alkyl halides, nitrosos, and tosylates have been used in the intermolecular or intramolecular conjugate addition/electrophilic trapping reactions for the construction of complex molecular frameworks through tandem processes. As with the carbon electrophile, imines might be another attractive substrate for the conjugate addition/electrophilic trapping reaction. However, to the best of our knowledge, the use of this type of synthetically versatile aldimine as the terminal electrophile for this kind of reaction remains unexplored—presumably owing to their relatively lower electrophilicity in comparison with aldehydes and other carbonyl-containing electrophiles. Moreover, most of the stereoselective tandem reactions of this kind install the stereogenic centers on cyclic compounds. This limitation is probably due to difficulty in the stereoselective construction of contiguous stereogenic centers in acyclic compounds as compared to cyclic systems. Herein we report a highly diastereoand enantioselective construction of three contiguous acyclic stereogenic centers through a copper-catalyzed tandem conjugate addition/Mannich reaction of organozinc reagents and acyclic a,b-unsaturated ketones in the presence of imines to afford b-aminocarbonyl derivatives (Scheme 1). Thus, allowing the asymmetric synthesis of chiral azetidines in high enantioselectivity. Notably, in a one-pot manipulation, chiral isoindolinones can also be obtained with high levels of relative and absolute stereochemical control by using this method. First, we investigated the reactivity of several types of imines as electrophiles toward the chalcone 1 and Et2Zn in the presence of Cu(CH3CN)4BF4 (1 mol%) and with (S,S)-L1 (1.2 mol%) as a chiral ligand in toluene at 10 8C for 12 hours—these are the same reaction conditions that previously led to good results for the copper-catalyzed conjugate Michael addition protocol. The desired tandem reactions did not proceed with either N-arylimine or N-alkylimine, and only the 1,4-conjugate addition products were obtained. However, the use of N-tosyl aldimine 2a as an electrophile under the same reaction conditions gave the desired tandem adduct in 72% yield with good enantioselectivity (76% ee) for the major diastereomer (Table 1, entry 1). Also, only two of the four possible diastereomers were detected. This exceptionally high reactivity may be attributed to the higher electrophilicity of the N-tosyl aldimine or the strong coordination of the copper ion to the N-tosyl aldimine through a 1,3binding mode of the nitrogen atom of the imine moiety and the oxygen atom of the sulfonyl group. We then focused our attention on this type of imine as the electrophilic tapping reagent and examined several catalytic systems. We used chalcone 1a, N-tosyl aldimine 2a, and Et2Zn as the reactants, and the reaction was performed at 10 8C in toluene for 12 hours. With L1 as a ligand, we screened a variety of copper sources including copper(I) and copper(II) species, and found the stereoselectivity was significantly affected by the nature of the counterion of the copper salts (Table 1, entries 1–8). The more coordinating counterions proved to be more suitable, and among those tested, CuBr led to the best results with respect to reactivity and stereoselectivity (Table 1, entry 3). Among the solvents [*] S. Guo, Y. Xie, Prof. Dr. X. Hu, Prof. Dr. C. Xia, Prof. Dr. H. Huang State Key Laboratory for Oxo Synthesis and Selective Oxidation Lanzhou Institute of Chemical Physics Chinese Academy of Sciences, Lanzhou, 730000 (China) Fax: (+ 86)931-496-8129 E-mail: hmhuang@licp.cas.cn

Enantioselective epoxidation of olefins catalyzed by two novel chiral poly-salen-Mn(III) complexes

Two novel chiral poly-salen–Mn(III) complexes 1 and 2, derived from (R,R)-1,2-diaminocyclohexane and the disalicylaldehydes 5 and 6 were synthesized and employed in the enantioselective epoxidation of olefins. A range of 30–92% ee and 75–97% yield was achieved in NaClO/4-PPNO and m-CPBA/NMO oxidant systems when substituted styrenes and substituted 2,2-dimethylchromenes were used as substrates. Furthermore, the poly-salen–Mn(III) complexes could be recovered easily and recycled efficiently several times by a simple catalysis/separation method. After five reactions, an 82% ee and 78% yield of epoxide were obtained using 2,2-dimethylchromene as substrate.

Highly enantioselective resolution of terminal epoxides using polymeric catalysts

Poly-salen-Co(III) complexes were employed in the hydrolytic kinetic resolution (HKR) of terminal epoxides and ees up to 98% were obtained. In the HKR of epichlorohydrin, the polymeric catalysts can be recovered and modified for recycling. The recovered polymer catalyst shows good activity and selectivity.

Ferrocenylphosphine-imine ligands for Pd-catalyzed asymmetric allylic alkylation

Ferrocenylphosphine-imine ligands 6 derived front (r,s)-ppfnh2-r 5 and a variety of benzaldehydes were applied in the pd-catalyzed asymmetric allylic alkylation of 1,3-diphenylprop-2-en-1-yl acetate 7a or pivalate 7b with dimethyl malonate. the substituent effects on the catalytic reaction were investigated, and 96% e.e. with 99% yield was achieved when the m-nitro substituted ligand 6k was used. (c) 2002 elsevier science ltd. all rights reserved.

All-normal dispersion, figure-eight, tunable passively mode-locked fiber laser with an invisible and changeable intracavity bandpass filter

We report dissipative solitons generation in the figure-8 all-normal dispersion fiber ring laser. The steep edge of the output optical spectrum results from the filtering effect of NOLM together with polarization controllers (PCs). No any physical bandpass filters are used in the cavity. Moreover, the output wavelength can be tuned in a wide range of about 20 nm. In the long-wavelength region, the spectral filtering effect of NOLM becomes weaker and output spectrum shows only one steep side. Filtering effect can perform periodically with increasing the pump power. The highly chirped pulse has good potential for application to the chirped pulse amplification (CPA) system.

A general and facile one-pot process of isothiocyanates from amines under aqueous conditions

Summary A general and facile one-pot protocol for the preparation of a broad range of alkyl and aryl isothiocyanates has been developed from their corresponding primary amines under aqueous conditions. This synthetic process involves an in situ generation of a dithiocarbamate salt from the amine substrate by reacting with CS2 followed by elimination to form the isothiocyanate product with cyanuric acid as the desulfurylation reagent. The choice of solvent is of decisive importance for the successful formation of the dithiocarbamate salt particularly for highly electron-deficient substrates. This novel and economical method is suitable for scale-up activities.

Highly diastereo- and enantioselective tandem reaction toward functionalized pyrrolidines with multiple stereocenters.

An efficient asymmetric tandem dual Michael reaction that constructs three contiguous stereocenters in acyclic open-chain systems with very high enantioselectivity and diastereoselectivity has been developed. This protocol provides a reliable and rapid approach for synthesis of chiral pyrrolidines with multiple stereocenters.

Structural probing of d-fructose derived ligands for asymmetric addition of diethylzinc to aldehydes

Abstract A series of new chiral ligands derived from d -fructose have been synthesized and applied in the enantioselective addition of diethylzinc to aldehydes. Comparison of the enantioselectivities obtained with these ligands demonstrated that the catalytic properties are highly dependent upon the structure of ligands, a rational explanation of the structural effects on the catalytic properties is provided.

Highly enantioselective resolution of terminal epoxides with cross-linked polymeric salen-Co(III) complexes

Abstract Crosslinked polymeric salen–Co(III) complexes derived from a novel dialdehyde and a trialdehyde were synthesized and employed in the hydrolytic kinetic resolution (HKR) of terminal epoxides. Up to 99% ee were obtained with only 0.16–0.02 mol% of catalyst (based on catalytic unit).