β-Silylacrylate as a Multipurpose Reagent in Organic Synthesis

Acrylates are well known electrophilic alkenes having multitude of applications in organic synthesis. They are very good acceptors in Michael addition reactions and are good enophile/dienophile/dipolarophile partners in cycloaddition reactions. Replacing the β-alkyl/aryl groups in acrylates by a silicon group would be interesting. In addition to the conventional reactions displayed by acrylates, β-silylacrylates (β-SAs) can show reactivity specifically related to the silicon group. Many conventional organic reactions such as hydrodimerization, organocatalytic asymmetric Michael additions, inter- and intra-molecular Diels–Alder reactions, and asymmetric 1,3-dipolar cycloadditions have been used to generate the complex chemical entities from β-SAs. Some of the reaction outcomes were vastly influenced by the silicon substituent. This review describes the practical synthesis β-SAs and their use as starting point in complex molecule generation including total synthesis of some natural products/bioactive molecules.     

Synthesis and characterization of α-{ 3-[2-hydroxy-3- （N-methyl-N-hydroxy-ethylamino）propoxy]propyl}-ω- butylpolydimethylsiloxanes

α-{ 3-[2-hydroxy-3-（N-methyl-N-hydroxyethylamino）propoxy]propyl }-α-butylpolydimethylsiloxanes III with various molecu- lar weights were prepared by epoxy addition of α-[3-（2,3-epoxy-propoxy）propyl]-α-butylpolydimethylsiloxanes Ⅱ and N- methylmonoethanolamine. At each step, the outcome compounds were characterized through FT-IR and NMR spectra, the results showed that each step was successfully carried out and objective products were achieved.     

An Electron-Deficient Triosmium Cluster Containing the Thianthrene Ligand: Synthesis, Structure and Reactivity of [Os3(CO)9(μ3-η2-C12H7S2)(μ-H)]

Reaction of [Os₃(CO)₁₀(CH₃CN)₂] with thianthrene at 80 °C leads to the nonacarbonyl dihydride compound [Os₃(CO)₉(μ-3,4-η²-C₁₂H₆S₂)(μ-H)₂] (1) and the 46-electron monohydride compound [Os₃(CO)₉(μ₃-η²-C₁₂H₇S₂)(μ-H)] (2). Compound 2 reacts reversibly with CO to give the CO adduct [Os₃(CO)₁₀(μ-η²-C₁₂H₇S₂)(μ-H)] (3) whereas with PPh₃ it gives the addition product [Os₃(CO)₉)(PPh₃)(μ-η²-C₁₂H₇S₂)(μ-H)] (4) as well as the substitution product 1,2-[Os₃(CO)₁₀((PPh₃)₂] (5) Compound 2 represents a unique example of an electron-deficient triosmium cluster in which the thianthrene ring is bound to cluster by coordination of the sulfur lone pair and a three-center-two-electron bond with the C(2) carbon which bridges the same edge of the triangle as the hydride. Electrochemical and DFT studies which elucidate the electronic properties of 2 are reported. Dedicated to the memory of a great scientist, F. Albert Cotton.     

Size of Monochromatic Double Stars in Edge Colorings

We show that in every r-coloring of the edges of K _n there is a monochromatic double star with at least \(\frac{n(r+1)+r-1}{r^2}\) vertices. This result is sharp in asymptotic for r = 2 and for r≥ 3 improves a bound of Mubayi for the largest monochromatic subgraph of diameter at most three. When r-colorings are replaced by local r-colorings, our bound is \(\frac{n(r+1)+r-1}{r^2+1}\).     

The future of reversible addition fragmentation chain transfer polymerization

We examine the reversible addition fragmentation chain transfer (RAFT) process with regard to its potential and limits in future industrial applications (including those conducted on a larger scale) as well as materials science. The outlook for the RAFT process is bright: Its unrivaled inherent process simplicity coupled with a wide tolerance to monomer classes and functionalities makes it a prime candidate for the use in large reactors. At the same time, it allows for ready access to complex macromolecular architectures of variable shape and size. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5715–5723, 2008     

Bimolecular radical termination: New perspectives and insights

The reversible addition‐fragmentation chain transfer‐chain length dependent termination (RAFT‐CLD‐T) method has allowed us to answer a number of fundamental questions regarding the mechanism of diffusion‐controlled bimolecular termination in free‐radical polymerization (FRP). We carried out RAFT‐mediated polymerizations of methyl acrylate (MA) in the presence of a star matrix to develop an understanding of the effect of polymer matrix architecture on the termination of linear polyMA radicals and compared this to polystyrene, polymethyl methacrylate, and polyvinyl acetate systems. It was found that the matrix architecture had little or no influence on termination in the dilute regime. However, due to the smaller hydrodynamic volumes of the stars in solution compared to linear polymer of the same molecular weight, the gel onset point occurred at greater conversions, and supported the postulate that chain overlap (or c*) is the main cause for the observed autoacceleration observed in FRP. Other theories based on “short–long” termination or free‐volume should be disregarded. Additionally, since our systems are well below the entanglement molecular weight, entanglements should also be disregarded as the cause of the gel onset. The semidilute regime occurs over a small conversion range and is difficult to quantify. However, we obtain accurate dependencies for termination in the concentrated regime, and observed that the star polymers (through the tethering of the arms) provided constriction points in the matrix that significantly slow the diffusion of linear polymeric radicals. Although, this could at first sight be postulated to be due to reptation, the dependencies showed that reptation could be considered only at very high conversions (close to the glass transition regime). In general, we find from our data that the polymer matrix is much more mobile than what is expected if reptation were to dominate. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3155–3173, 2008     

(20S)-20-羟基胆甾烷-3,16-二酮的合成

以妊娠双烯醇酮醋酸酯为起始原料, 经过7步反应以13.1%的总收率合成了一个具有抗4种肿瘤细胞(ED₅₀＝1 μg/mL)的海洋天然产物(20S)-20-羟基胆甾烷-3,16-二酮. 关键反应为底物控制的不对称杂原子共轭加成反应.     

Synthesis of well‐defined polymeric activated esters

Monomers bearing an activated ester group can be polymerized under various controlled polymerization techniques, such as ATRP, NMP, RAFT polymerization, or ROMP. Combining the functionalization of polymers via polymeric activated esters with these controlled polymerization techniques generate possibilities to realize highly functionalized polymer architectures. Within this highlight two different research areas of activated esters in polymer science will be discussed: (i) the preparation of defined reactive polymer architectures by controlled polymerization techniques and (ii) the preparation of defined reactive thin films. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6677–6687, 2008