Chengxia Miao

Manganese Catalysts with C1-Symmetric N4 Ligand for Enantioselective Epoxidation of Olefins

the “Hundred Talents Program” of the Chinese Academy of Sciences and the National Natural Science Foundation of China (20873166;21073210;21133011)

Asymmetric 5-endo chloroetherification of homoallylic alcohols toward the synthesis of chiral β-chlorotetrahydrofurans

An asymmetric 5-endo chloroetherification of homoallylic alcohols is successfully developed that employs an easily available quaternary ammonium salt derived from cinchonine as a conventional organocatalyst. This approach provides ready access to β-chlorotetrahydrofurans in high enantioselectivities.

Magnetic Nanoparticles of Ferrite Complex Oxides: A Cheap, Efficient, Recyclable Catalyst for Building the CN Bond under Ligand‐Free Conditions

A series of magnetic nanoparticles of ferrite complex oxides were simply prepared by using a citric acid complex method and characterized by using XRD, FT‐IR spectroscopy, TEM, the BET nitrogen adsorption/desorption technique, and a vibrating sample magnetometer. The magnetic nanoparticles were used for the N‐arylation of nitrogen nucleophiles to form new CN bonds. CuFe2O4 nanoparticles calcined at 850 °C exhibited the best activity with moderate to excellent yields under ligand‐free conditions. Notably, CuFe2O4 is completely recoverable with an external magnet and can be reused eight times without significant loss of catalytic activity.

NHPI and ferric nitrate: a mild and selective system for aerobic oxidation of benzylic methylenes

A mild and selective system comprising N-hydroxyphthalimide (NHPI) and Fe(NO3)3·9H2O was developed for the oxidation of benzylic methylenes with an atmospheric pressure of molecular oxygen at 25 °C. The influences of reaction conditions such as solvent, different metal catalysts and catalyst loading were studied, as well as the kinetics of the oxidation reaction. Various benzylic methylene substrates could be oxidized to the corresponding carbonyl compounds in satisfactory yields with this catalytic system. Hammett analysis suggested that the substrates with electron-donating groups would have higher oxidation rates. Isotopic (18O) labeling experiments provided evidence of the participation of the nitrate anion in the catalytic cycle. In addition, a possible radical mechanism involving hydrogen atom abstraction by PINO (phthalimide-N-oxyl) and nitrate participation for the oxidation of benzylic methylenes in the Fe(NO3)3·9H2O/NHPI/O2 system was proposed.

The Direct Arylation of Unactivated Arenes with Aryl Halides Catalyzed by a Magnetically Recyclable Fe‐Ni Alloy

the Chinese Academy of Sciences and the National Natural Science Foundation of China (21073210;21133011)

A Salen–Co3+ Catalyst for the Hydration of Terminal Alkynes and in Tandem Catalysis with Ru–TsDPEN for the One-Pot Transformation of Alkynes into Chiral Alcohols

The cobalt–salen complex (C1:[(salen)Co3+(OAc)]; salen= N,N′‐bis(salicylidene)ethylenediamine, OAc=acetate) was found to efficiently promote the hydration of terminal alkynes to give methyl ketones in the presence of the H2SO4 cocatalyst. In addition, the one‐pot transformation of alkynes into chiral alcohols through tandem catalysis by catalyst C1 coupled with a ruthenium–TsDPEN complex (C3: [(R,R‐TsDPEN)Ru2+(cymene)]; TsDPEN=(1R,2R)‐N‐(p‐toluenesulfonyl)‐1,2‐diphenylethylenediamine, cymene=1‐methyl‐4‐(1‐methylethyl)benzene) catalyst was realized with excellent yields and enantioselectivities.

Magnetic Fe–Ni Alloy Catalyzed Suzuki Cross‐Coupling Reactions of Aryl Halides with Phenylboronic Acid

The Suzuki coupling reaction is an important method for the selective construction of biaryls, and this reaction has found extensive use in the synthesis of natural products, pharmaceuticals, and advanced materials. Over the past decade, palladium catalysts have been used commonly for Suzuki coupling reactions. 4] Considering the high cost of palladium, the use of much cheaper nickel catalysts has attracted considerable interest. Since the first report by Percec in 1995, remarkable advances have been made in the nickel-catalyzed version of the Suzuki reaction. The most commonly used Ni sources are the phosphine-coordinated nickel(II) halides. However, Ni complexes as precatalysts often need to be combined with a reducing agent such as Zn or BuLi to generate the Ni species in situ to achieve high efficiency of the catalysts. The nickel salts NiCl2 and NiCl2·6 H2O have also been used as precatalysts for the Suzuki reaction with nitrogen-containing ligands and without any ligands, respectively. Recently, the Ni-catalyzed Suzuki coupling reaction with the direct use of Ni(cod)2 was demonstrated. However, such a Ni source is difficult to handle in practice because of its high air sensitivity and toxicity. A common feature of most reported systems is the involvement of a homogeneous Ni catalyst. Despite significant progress towards the use of homogeneous nickel catalysts in the Suzuki reaction over the past few years, the recovery and recycling of the homogeneous catalysts and the contamination of the products by ligands and/or metals have not been addressed. Therefore, considering the need for large-scale or even industrial preparation, it remains highly desirable to develop more practical protocols, such as a heterogeneous catalytic system, for the Suzuki reaction. Hyeon et al. synthesized monodisperse nanoparticles of Ni and NiO with particle sizes of 2, 5, and 7 nm as catalysts for the Suzuki coupling reaction. Recently, a new heterogeneous catalyst composed of copper and nickel oxide particles supported within charcoal for the Suzuki–Miyaura reaction was developed by Lipshutz. However, there are few reports on the use of a magnetic heterogeneous catalyst for the Suzuki coupling reaction. In conjunction with a project on the development of magnetic nanoparticle catalysts, we attempted to use the magnetic Fe–Ni alloy as a catalyst for the Suzuki coupling reaction in the absence of a reducing agent. Fortunately, the coupling reaction of aryl halides with phenylboronic acid proceeded smoothly in the presence of the Fe–Ni alloy to provide the desired products in satisfactory to excellent yields. Procedures for the preparation and characterization of the Fe–Ni alloy were described earlier. The initial experiments were carried out by testing the protocol and screening the reaction conditions with 4-iodoanisole and phenylboronic acid as model substrates (Table 1). Obviously, the Fe–Ni alloy and ligand were essential for the coupling reaction (Table 1, entries 1–3). Fortunately, 95 % yield could be obtained with Cy3P as the ligand and NaOH as the base at 120 8C in 2 mL dioxane (Table 1, entry 4). It was found that the reaction temperature had a significant influence on the yields. The yield was reduced to 90 % when the temperature decreased to 110 8C (Table 1, entry 5), and the reaction did not proceed at a temperature of 90 8C (Table 1, entry 6). Subsequently, solvent effects were also investigated (Table 1, entries 4, 7–10), and dioxane was found

Facile and highly chemoselective synthesis of benzil derivatives via oxidation of stilbenes in an I2–H2O system

A facile and highly chemoselective protocol for the synthesis of benzil derivatives has been developed by oxidation of stilbenes in an I2–H2O system under air. Notably, the method was applicable to 26 examples and provided up to 98% yield, avoiding the use of acid, metal catalysts and so on.

Merging the ring opening of benzoxazoles with secondary amines and an iron-catalyzed oxidative cyclization towards the environmentally friendly synthesis of 2-aminobenzoxazoles

A facile and environmentally friendly method was developed through merging the ring opening of benzoxazoles with secondary amines and an iron-catalyzed oxidative cyclization towards the synthesis of 2-aminobenzoxazoles. In the oxidative cyclization step, with catalytic amounts of FeCl and aqueous H2O2 as a green oxidant, highly desirable 2-aminobenzoxazoles were isolated in excellent yields of up to 97%. A plausible radical process is proposed for the oxidative cyclization on the basis of mechanistic studies.

CuI/N4 ligand/TEMPO derivatives: A mild and highly efficient system for aerobic oxidation of primary alcohols

Abstract A new system consisting of a copper(I) complex generated in situ from a tetradentate nitrogen ligand and CuI in combination with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) derivatives was successfully developed. The system was suitable for efficient and selective aerobic oxidation of primary benzyl and allyl alcohols with a wide range of functional groups to the corresponding aldehydes at room temperature. The best result was obtained with N,N’ -dimethyl- N,N’ -bis(2-pyridylmethyl)ethane-1,2-diamine as the ligand and 4-OH-TEMPO as a cocatalyst in CH 3 CN. In addition, high-resolution mass spectrometry, ultraviolet-visible spectroscopy, and electrochemical experiments were used to provide evidence of intermediates.