Cyclobutanes in catalysis

The exploitation of ring strain as a driving force to facilitate chemical reactions is a well‐appreciated principle in organic chemistry. The most prominent and most frequently used compound classes in this respect are oxiranes and cyclopropanes. For rather a long time, cyclobutanes lagged behind these three‐membered‐ring compounds in their development as reactive substrates, but during the past decade an increasing number of useful reactions of four‐membered‐ring substrates have emerged. This Minireview examines corresponding catalytic reactions ranging from Lewis or Brønsted acid catalyzed processes to enzymatic reactions. The main focus is placed on transition‐metal‐catalyzed C C bond‐insertion and β‐carbon‐elimination processes, which enable exciting downstream reactions that deliver versatile building blocks.     

Characterization of the micellar ring opening metathesis polymerization in water of a norbornene derivative initiated by Hoveyda‐Grubbs' catalyst

Solubilization of the hydrophobic Hoveyda‐Grubbs' catalyst in micellar aqueous phase has been achieved using dodecyl and cetyl ammonium chloride as surfactants. The domain of solubilization has been estimated before carrying out ring‐opening metathesis polymerization in these micellar solutions with a hydrophilic monomer. Kinetics orders have been determined relative to monomer, initiator, and surfactant. A good control of the molecular weight has been obtained for ratios [micelles]/[initiator] over 1. The better control of the polymerization obtained in micellar solution has been explained by a difference of reactivity leading to a more efficient initiation step in the presence of the micelles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2833–2844, 2008     

分子中的环识别算法

对于化合物结构自动解析系统来说,环的处理是必须的^[1~4],本文设计了环识别模块,该模块以从化合物的二维连接表出发,先获得化合物中的所有环,进一步得到最大环和最小环,并作为环约束,以增加ESESOC系统结构生成器的有效性。     

KINETICS OF THE CHROMIUM(II) REDUCTIONS OF CHELATED AMINO ACIDO-BIS(ETHYLENE-DIAMINE)COBALT(III) COMPLEXES

Abstract

The kinetics of Cr²⁺(aq) reductions of glycinato-, D,L-alanato, D,L-phenylalanato-, and D,L-leucinatobis-(ethylenediamine)cobalt(III) ions have been investigated. The rate law is of the form d(ln[Co(III)]/dt = k[Cr²⁺], where the rate constant k(M^?1sec^?1) and associated activation parameters δH^δ(kcal mol^?1 and δS^δ (cal deg ^?1mol^?1) in parentheses, are respectively 1.65 · 0.06 (9.7 · 0.1, -25 · 1), 0.367 · 0.008 (10.9 · 04,-24 ·1), 0.529 · 0.021 (11.2 · 0.4, -22 · 1); and 0.358 · 0.019 (11.5 · 0.3, -22 · 1) at 298^·K and ·[CIO·] = 1.0 M. The reactions are all inner-sphere.     

Rhodium(I)‐Catalyzed Enantioselective C?C Bond Activation

Relieving the strain : The rhodium(I)‐catalyzed activation of C C bonds in functionalized cyclobutanes opens a novel route to highly substituted carbo‐ and heterocycles. Particularly intriguing is the differentiation of enantiotopic C C bonds, which leads to the formation of highly enantiomerically enriched lactones, cyclopentanones, and cyclohexenones (see scheme).

     

Rhodium(I)‐Catalyzed Enantioselective Activation of Cyclobutanols: Formation of Cyclohexane Derivatives with Quaternary Stereogenic Centers

The activation of carbon–carbon σ bonds is a complementary method to access uncommon and difficult‐to‐prepare organometallic species. Herein, we describe the activation of tert‐cyclobutanols through an enantioselective insertion of a chiral rhodium(I) complex into the C? C σ bond of the cyclobutane, forming a quaternary stereogenic center and an alkyl‐rhodium functionality that initiates ring‐closure reactions. This technology provides access to a variety of substituted cyclohexane derivatives with quaternary stereogenic centers. The formation of different product families can be controlled by the employed set of reaction conditions and additives. In general, high yields and excellent enantioselectivities of up to 99 % ee are obtained.     

Synthesis and Spectra of Bichromophore Compounds Containing Oxazole or Oxadiazole Ring

Fifteen of the bichromophore compounds containing oxazole or oxidation ring have been synthesized. Their structures have been identified by IR, 1H NMR spectra and elemental analysis. The UV spectra, fluorescence spectra and the laser conversion efficiencies have been determined . The results of determination show that the absorption and emission spectra Pf the bichromophore compounds are different from those of the corresponding single chromophore compounds.     

Simple and Convenient Synthesis of 4‐Unsubstituted‐3‐(3‐Oxoalkyl)isocoumarins

A simple transformation of 2‐alkylfurans and 2‐formylbenzoic acids into 4‐unsubstituted 3‐(3‐oxoalkyl)isocoumarins is described. It is based on the synthesis of 2‐(2‐carboxybenzyl)furans followed by their acid‐catalyzed recyclization to the target isocoumarins.