Control of Vicinal Stereocenters through Nickel-Catalyzed Alkyl-Alkyl Cross-Coupling

Vicinal stereocenters are found in many natural and unnatural compounds. Although metal-catalyzed cross-coupling reactions of unactivated alkyl electrophiles are emerging as a powerful tool in organic synthesis, there have been virtually no reports of processes that generate, much less control, vicinal stereocenters. In this investigation, we establish that a chiral nickel catalyst can mediate doubly stereoconvergent alkyl–alkyl cross-coupling, specifically, reactions of a racemic pyrrolidine-derived nucleophile with cyclic alkyl halides (as mixtures of stereoisomers) to produce vicinal stereocenters with very good stereoselectivity

Research and Design of a Routing Protocol in Large-Scale Wireless Sensor Networks

无线传感器网络，作为全球未来十大技术之一，集成了传感器技术、嵌入式计算技术、分布式信息处理和自组织网技术，可实时感知、采集、处理、传输网络分布区域内的各种信息数据，在军事国防、生物医疗、环境监测、抢险救灾、防恐反恐、危险区域远程控制等领域具有十分广阔的应用前景。 本文研究分析了无线传感器网络的已有路由协议，并针对大规模的无线传感器网络设计了一种树状路由协议，它根据节点地址信息来形成路由，从而简化了复杂繁冗的路由表查找和维护，节省了不必要的开销，提高了路由效率，实现了快速有效的数据传输。 为支持此路由协议本文提出了一种自适应动态地址分配算——ADAR（AdaptiveDynamicAddre...As one of the ten high technologies in the future, wireless sensor network, which is the integration of micro-sensors, embedded computing, modern network and Ad Hoc technologies, can apperceive, collect, process and transmit various information data within the region. It can be used in military defense, biomedical, environmental monitoring, disaster relief, counter-terrorism, remote control of haz...学位：工学硕士院系专业：信息科学与技术学院通信工程系_通信与信息系统学号：2332007115216

Nickel-catalysed carboxylation of organoboronates

The authors acknowledge the ERC (Advanced Researcher award-FUNCAT, CO2Chem) and King Saud University for funding and the EPSRC NMSSC in Swansea for mass spectrometric analyses. SPN is a Royal Society Wolfson Research Merit Award holder.A nickel/N-heterocyclic carbene (NHC) catalysed carboxylation of aryl-, heteroaryl- and alkenylboronates, affording the corresponding carboxylic acids, has been developed. This transformation proceeds under one atmosphere of CO2 with a broad range of substrates and exhibits good functional group compatibility.Publisher PDFPeer reviewe

Enhanced activity of [Ni(NHC)CpCl] complexes in arylamination catalysis

Seven new air- and moisture-stable nickel complexes bearing flexible bulky NHC (N-heterocyclic carbene) ancillary ligands (NHC = IPr*, IPrTol*, IPrOMe*, IPent) are reported. Using experimentally determined crystal structures, the steric environments of [Ni(NHC)CpCl] complexes were analyzed. A survey of their catalytic activity in Buchwald-Hartwig arylamination has been performed. In comparison to less sterically demanding analogues (NHC = IMes, SIMes, IPr, SIPr), an increase in the ligand bulkiness was found to correlate to a dramatic enhancement of the C-N bond formation efficiency. Finally, the catalytic activity of the most active precatalyst, [Ni(IPrOMe*)CpCl], was further explored and the scope and limitations of this complex were examined

Ruthenium-Catalyzed Chemo- and Enantioselective Hydrogenation of Isoquinoline Carbocycles

A chemoselective hydrogenation of isoquinoline carbocycles was achieved by using the catalyst prepared from Ru­(methallyl)₂(cod) and <i>trans</i>-chelate chiral ligand PhTRAP. The unique chemoselectivity achieved in this hydrogenation could be ascribed to the <i>trans</i>-chelation of the chiral ligand. The procedure for preparing the catalyst strongly affects the reproducibility of the carbocycle hydrogenation. Various 5-, 6-, 7-, and 8-substituted isoquinolines were selectively hydrogenated at their carbocycles to afford 5,6,7,8-tetrahydroisoquinolines as major products in high yields with moderate or good enantioselectivities. Some mechanistic studies suggested that the stereogenic center was created during the initial addition of H₂ to the aromatic ring in the hydrogenation of 5-substituted isoquinolines. In other words, the stereochemical control was accompanied by the dearomatization

Ruthenium-Catalyzed Chemo- and Enantioselective Hydrogenation of Isoquinoline Carbocycles

A chemoselective hydrogenation of isoquinoline carbocycles was achieved by using the catalyst prepared from Ru­(methallyl)₂(cod) and <i>trans</i>-chelate chiral ligand PhTRAP. The unique chemoselectivity achieved in this hydrogenation could be ascribed to the <i>trans</i>-chelation of the chiral ligand. The procedure for preparing the catalyst strongly affects the reproducibility of the carbocycle hydrogenation. Various 5-, 6-, 7-, and 8-substituted isoquinolines were selectively hydrogenated at their carbocycles to afford 5,6,7,8-tetrahydroisoquinolines as major products in high yields with moderate or good enantioselectivities. Some mechanistic studies suggested that the stereogenic center was created during the initial addition of H₂ to the aromatic ring in the hydrogenation of 5-substituted isoquinolines. In other words, the stereochemical control was accompanied by the dearomatization

[Au]/[Pd] Multicatalytic processes : direct one-pot access to benzo[c]chromenes and benzo[b]furans

A new synthetic protocol that combines the advantages offered by eco-friendly solvent-free reactions and sequential transformations is reported. This strategy offers straightforward access to benzo[c]chromenes and benzo[b]furans from commercially available starting materials. This two-step, one-pot strategy consists of an Au-catalyzed hydrophenoxylation process followed by Pd-catalyzed CH activation or Mizoroki-Heck reactions. The selectivity of the process towards CH activation or Mizoroki-Heck reaction can be easily tuned

Reversible 1,3-<i>anti</i>/<i>syn</i>-Stereochemical Courses in Copper-Catalyzed γ-Selective Allyl–Alkyl Coupling between Chiral Allylic Phosphates and Alkylboranes

The stereochemical courses of the copper-catalyzed allyl–alkyl coupling between enantioenriched chiral allylic phosphates and alkylboranes were switchable between 1,3-<i>anti</i> and 1,3-<i>syn</i> selectivities by the choice of solvents and achiral alkoxide bases with different steric demands. The reactions with γ-silylated allylic phosphates allow efficient synthesis of enantioenriched chiral allylsilanes with tertiary or quaternary carbon stereogenic centers. Cyclic and acyclic bimodal participation of alkoxyborane species in an organocopper addition–elimination sequence is proposed to account for the phenomenon of the <i>anti</i>/<i>syn</i>-stereochemical reversal

Copper-Catalyzed Enantioselective Allylic Alkylation of Terminal Alkyne Pronucleophiles

The copper-catalyzed enantioselective allylic alkylation of terminal alkynes with primary allylic phosphates was developed by the use of a new chiral N-heterocyclic carbene ligand bearing a phenolic hydroxy group at the <i>ortho</i> position of one of the two <i>N</i>-aryl groups. This reaction occurred with excellent γ-branch regioselectivity and high enantioselectivity, forming a controlled stereogenic center at the allylic/propargylic position. Various terminal alkynes, including silyl, aliphatic, and aromatic alkynes, could be used directly without premetalation of the C­(sp)–H bond. On the basis of the results of experiments using an isomeric secondary allylic phosphate, which gave a branched product through an α-selective substitution reaction with retention of configuration, a reaction pathway involving 1,3-allylic migration of Cu in a ([σ + π]-allyl)­copper­(III) species is proposed