Efficient construction of tri- and tetracyclic heterocycles from linear 1,6-dienes by a domino reaction

Tri- and tetracyclic heterocycle systems were constructed by a palladium-catalyzed domino reaction of linear 1,6-dienes that contain acryl groups with aryl halides through C-C coupling and aromatic C-H functionalization. Three different acrylamides have been shown to be very active for the reaction. The substituents on the aryl halides could be ethoxycarbonyl, ketyl, chloro, sulfonyl, cyano, etc. Thus, the ready accessibility of the starting materials, the wide range of compatibility of substrates including both dienes and aryl halides, and the generality of this process make the reaction highly valuable in view of the synthetic and medicinal importance of these kinds of heterocycles.     

Ligand-free Sonogashira coupling reactions with heterogeneous Pd/C as the catalyst

A variety of aryl iodides were coupled with aromatic and aliphatic terminal alkynes to give the corresponding 1,2-disubstituted aromatic alkynes in good yields by using only 0.4 mol % of the heterogeneous 10 % Pd/C as the catalyst without a ligand, copper salt, or amine in an aqueous medium.     

Pd-catalyzed aryl amination mediated by well defined, N-heterocyclic carbene (NHC)-Pd precatalysts, PEPPSI

Pd-N-heterocyclic carbene (NHC)-catalyzed Buchwald-Hartwig amination protocols mediated by Pd-PEPPSI precatalysts is described. These protocols provide access to a range of hindered and functionalized drug-like aryl amines in high yield with both electron-deficient and electron-rich aryl- and heteroaryl chlorides and bromides. Variations in solvent polarity, base and temperature are tolerated, enhancing the scope and utility of this protocol. A mechanistic rationalization for base strength (pKb) requirements is also provided.     

Palladium-catalyzed formation of highly substituted naphthalenes from arene and alkyne hydrocarbons

Several highly substituted naphthalenes 3 have been synthesized in a one-pot reaction by treatment of arenes 1 with alkynes 2 in the presence of palladium acetate and silver acetate. In this Pd-catalyzed protocol, an arene provides a benzo source for the construction of a naphthalene core through twofold aryl C-H bond activation. Reaction of triphenylphosphine with diphenylethyne (2 a) under the catalysis of Pd(IV) complexes produced 1,2,3,4-tetraphenylnaphthalene (3 ba) in 62 % yield. Here, triphenylphosphine undergoes one aryl C-P bond cleavage and one aryl C-H bond activation to serve as a benzo moiety. Crystal structures of cycloadducts 3 ea, 3 ga, and 3 ac have been analyzed. The twisted naphthalenes arise not only from the overcrowded substituents but also from the contribution of the CH(3)-pi interaction.     

Generation of an aromatic amide-derived phosphane (Aphos) library by self-assisted molecular editing and applications of Aphos in room-temperature Suzuki-Miyaura reactions

Aromatic amide-derived phosphanes (Aphos) are hemilabile P,O-coordinating ligands, which, when combined with a Pd precursor, yield a promising precatalyst system for Suzuki-Miyaura cross-coupling reactions. A focused library of Aphos ligands has been constructed for structural optimization, with the target of improving catalytic efficacy. By using microwave irradiation at accurately regulated temperature, an expeditious and reproducible one-pot synthesis and screening protocol was designed and experimentally validated. The success is based on a unique self-assisted molecular editing (SAME) process in which both the substrate and the product molecules catalyze formation of the product. Thus, starting from a 4-chlorobenzamide-derived Aphos as the substrate, parallel reactions with a selected set of arylboronic acids, in the absence of an added external phosphane ligand to Pd, produced a family of structurally edited Aphos ligands. The resultant reaction mixture containing the new Aphos, the Pd species, and the base could be used for in situ screening of the Aphos efficacy in a reference Suzuki-Miyaura coupling reaction. The structures of all Aphos ligands were characterized by 31P NMR spectroscopy and their catalytic profiles in the reference reaction were evaluated by HPLC analysis. These data allowed the identification of an efficient Aphos ligand, capable of promoting room-temperature Suzuki-Miyaura coupling of unactivated and sterically hindered aryl chlorides with arylboronic acids under mildly basic conditions.     

聚L-酪氨酸/半胱氨酸/纳米金修饰Pt电极固定血红蛋白测定H2O2

制备了聚L-酪氨酸/半胱氨酸/纳米金/血红蛋白修饰Pt电极,并用循环伏安法和交流阻抗法对制备过程进行了表征。还用循环伏安法和计时电流法研究了修饰电极与H2O2的相互作用。结果表明,该电极对H2O2有明显的催化作用,电流与H2O2浓度在3.5×10-7~2.0×10-3mol/L范围内呈线性关系,检出限为1.0×10-7mol/L。     

Heterogenous catalytic method for the synthesis of biquinolines and bipyridines

A method has been developed for the synthesis of 2,2′- and 3,3′-biquinolines and of 4,4′-bipyridine based on the coupling of 2- and 3-bromoquinoline or 4-bromopyridine using a Pd/C-hydrazine-KOH catalytic system. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1839–1840, December, 2008.     

Pd(II)-Catalyzed Benzimidazole-Assisted Annulation of 3-(1H-Benzo[d]imidazol-2-yl)-2H-chromen-2-one: Access to Imidazo[1,2-a]chromeno[3,4-c]pyridine

Palladium-catalyzed [4+2] oxidative annulation of coumarin-benzimidazoles with olefins for the synthesis of polycyclic aromatic hydrocarbons have been achieved. This synthetic protocol gives access to a wide range of structurally distinct imidazo[1,2-a]chromeno[3,4-c]pyridines in moderate to good yield with wide functional group tolerance. Further, photophysical properties of annulated scaffolds have been examined, which discloses their interesting solvatochromic emission behaviors.     

Pd(II)/Lewis Acid Catalyzed Intramolecular Oxidative C−H Amination to Construct Carbazoles with Dioxygen

Transition-metal-catalyzed oxidative C−H amination reactions are among the most attractive topics in organic synthesis to construct nitrogen-containing motifs. The challenge is that most of these reactions employed stoichiometric oxidants to achieve satisfied catalytic efficiencies. Herein, we report a Pd(II)/LA-catalyzed (LA: Lewis acid) oxidative C−H amination reaction of 2-acetaminobiphenyls to construct carbazoles by using dioxygen balloon as the sole oxidant source, and the presence of LA sharply improved the catalytic efficiency of Pd(OAc)₂. Remarkably, in certain cases, the deacetylation of the annulation product happened under standard conditions to afford free carbazoles as the final product. The H/D exchange studies confirmed the reversibility of C−H activation and also disclosed multiple C−H activation sites by using −NAc and −NTs as the directing groups. In addition, the palladacycle compound was identified through ¹H NMR characterizations and proved to be the intermediate prior to the carbazole formation.     

Palladium-Catalyzed Hydroaminocarbonylation of Olefins with Aliphatic Amines without Additives

Palladium-catalyzed hydroaminocarbonylation reactions of olefins using aliphatic amines were performed under carbon monoxide atmosphere. Despite the strong basicity of the applied nucleophiles, the targeted amides were successfully synthesized in the absence of acidic additives. Styrene, oct-1-ene and isoprene were transformed to the corresponding amide isomers in moderate to good isolated yields under optimized reaction conditions. Various aliphatic amines were used as N-nucleophiles. The effect of chiral diphosphines on product distribution, that is, on chemo-, regio- and enantioselectivities was also studied. Plausible explanation was given for the additive-free hydroaminocarbonylation reaction.