Total Synthesis of Crenulatan Diterpenes: Strategy and stereocontrolled construction of a bicyclic keto-lactone building block

The bicyclic keto lactone 26 was synthesized for the purpose of developing a viable route to marine diterpenes of the crenulatan type. Following the efficient conversion of (S)-citronellol ( 5 ) to the allylated alcohol 9a (Scheme 2), the αβ-unsaturated lactone 12 was efficiently accessed in preparation for stereocontrolled conjugate addition. The hydroxymethyl equivalent most suited to this task was (i-PrO)Me₂SiCH₂MgCl, which gave 13 predominantly in the presence of CuI and Me₃SiCl. Once the OH group was deprotected (→ 14 ), it proved an easy matter to implement acid-catalyzed isomerization to lactone 15 , oxidation of which gave the pivotal aldehyde 16 . Condensation of 16 with PhSeCH₂Li led via 21 to 22 (Scheme 3). Once the OH group was protected (→ 22b ), it proved possible to effect aldolization with crotonaldehyde (→ 23 ). Exposure of 23 to acid gave the sub-target compound 25 . Its subsequent oxidation and thermal activation resulted in sequential selenoxide elimination with Claisen rearrangement (→ 26 ). The structural features of 26 require that a chair-like transition state be adopted during the [3.3]sigmatropic event. With the clarification of these issues, a highly serviceable and more advanced assault on the crenulatans should prove capable of being mounted.     

Reaction of triphenylphosphine with phenylethanethiolate-protected Au38 nanoparticles

The replacement of phenylethanethiolate (SC2Ph) ligands on 1.1 nm (core diameter) Au38(SC2Ph)24 monolayer-protected clusters (MPCs) with varied amounts of triphenylphosphine (PPh3) is investigated in methylene chloride. UV-vis spectra suggest that changes in the MPC Au core size occur when large amounts (> 10 equiv moles per cluster) of PPh3 are reacted with Au38(SC2Ph)24. 1H and 31P NMR spectra following the addition of smaller amounts (< 5 equiv moles) of PPh3 indicate that the reaction liberates a AuISC2Ph complex, as opposed to a SC2Ph thiol, disulfide, or anion. A 1H NMR kinetic study shows that the exchange is surprisingly rapid, even faster than exchanges of thiolates with other thiolates, at room temperature and in air. The reaction is slowed when cooled or conducted under Ar. The difference in potentials of the initial one-electron voltammetric reduction and oxidation of Au38(SC2Ph)24 decreases slightly upon reaction with small amounts of PPh3.     

Chiral metallacyclophanes: self-assembly, characterization, and application in asymmetric catalysis

[structure: see text] A family of chiral metallacyclophanes has been readily assembled based on robust Pt-acetylide linkage and characterized by a variety of spectroscopic techniques and X-ray crystallography. The steric congestion around the chiral dihydroxy groups in rigid metallacyclophane 4 prevents their reactions with Ti(O(i)()Pr)(4) to form active catalysts for enantioselective diethylzinc additions to aromatic aldehydes. In contrast, chiral dihydroxy groups in more flexible unclosed metallacyclophane 5 are effective ligands for enantioselective catalytic diethylzinc additions to aromatic aldehydes.     

富烯碳原子簇的石墨层间闭合形成机理

本文提出了富烯碳原子簇的石墨层间闭合形成机理，由该机理推出的许多结果与实验事实符合很好。我们认为碳原子簇自由基的快速淬灭及其淬灭速度是富烯碳原子簇形成及其丰度的决定因素。由此得出富烯碳原子簇在给定实验条件下产生的必然性，并预言不同大小的富烯碳原子簇可以通过优化实验条件选择性地合成。     

Fluorous Synthesis of Biaryl-Substituted Proline Analogs by 1,3-Dipolar Cycloaddition and Suzuki Coupling Reactions

A solution-phase synthesis of bicyclic prolines containing four points of diversity has been developed by a two-step synthesis involving 1,3-dipolar cycloaddition of perfluoroalkylsulfonyl-protected hydroxybenzaldehydes followed by Pd-catalyzed Suzuki coupling reaction of fluorous sulfonates with boronic acids. Both reactions are conducted under microwave irradiation and reaction mixtures are purified by solid-phase extractions without performing chromatography.     

Determination of mercury in human urine by neutron activation analysis,with lead diethyldithiocarbamate as a preconcentration agent

Lead diethyldithiocarbamate is an effective reagent for preconcentration of mercury in urine for neutron activation analysis. Sodium and bromine are removed from the sample by this procedure. As lead diethyldithiocarbamate is insensitive to neutron activation, radiochemical separation is not needed after neutron irradiation. Results from the analysis of urine collected from workers in caustic soda manufacturing plants are discussed.     

二芳基乙烯类光致变色材料的合成概述

由于具有多种潜在的应用价值, 光致变色化合物作为高级功能材料的研究在国内外广受关注. 在众多的有机光致变色化合物中, 二芳基乙烯特别是二噻吩乙烯, 由于其具有良好的热稳定性和优良的耐疲劳度而成为这类化合物的杰出代表. 近年来, 有关二芳基乙烯类光致变色化合物的各种合成及性能方面的报道已涉及到信息存储、分子开关、逻辑电路、液晶显示、磁性材料等众多领域. 主要是从有机合成的角度, 对这类材料的合成进行了较为全面的概括, 对各种合成方法分别加以介绍和分析, 对其发展趋势予以探索和展望.     

Sums of Fourier coefficients associated with Hecke cusp forms

Lithuanian Mathematical Journal - Let Hk denote the space of holomorphic Hecke cusp forms of even integral weight k for the full modular group Γ = SL(2, ℤ). Let λf (n), λg(n),...     

The Discrete Approximation of Continuous-state Nonlinear Branching Processes in Lévy Random Environments北大核心CSCD

In this paper, we establish the discrete approximation of continuous-state nonlinear branching processes in Lévy random environments by using tightness and convergence sequence in infinite dimensional product space via stochastic differential equations. Taking α-stable branching as an example, the conditions which are given to discretize continuous-state nonlinear branching processes in Lévy random environments are verified. © 2022 Chinese Academy of Sciences. All rights reserved.     

Convergence in Conformal Field Theory

Convergence and analytic extension are of fundamental importance in the mathematical construction and study of conformal field theory. The author reviews some main convergence results, conjectures and problems in the construction and study of conformal field theories using the representation theory of vertex operator algebras. He also reviews the related analytic extension results, conjectures and problems. He discusses the convergence and analytic extensions of products of intertwining operators (chiral conformal fields) and of q-traces and pseudo-q-traces of products of intertwining operators. He also discusses the convergence results related to the sewing operation and the determinant line bundle and a higher-genus convergence result. He then explains conjectures and problems on the convergence and analytic extensions in orbifold conformal field theory and in the cohomology theory of vertex operator algebras.