The first immobilization of pyridine-bis(oxazoline) chiral ligands

[formula: see text] A chiral pyridine-bis(oxazoline) ligand, functionalized with a vinyl group in the pyridine ring, can be polymerized with styrene and divinylbenzene to obtain supported chiral ligands. As proof of the usefulness of this supported ligands, the corresponding ruthenium complexes are catalysts for the cyclopropanation reaction of styrene with ethyl diazoacetate with up to 85% ee.     

Polymer-supported Bis(oxazoline)-copper complexes as catalysts in cyclopropanation reactions

Bis(oxazolines) are easily immobilized by functionalization of the central methylene bridge with polymerizable groups and subsequent polymerization. Polymers are transformed into copper catalysts active in the cyclopropanation of styrene with ethyl diazoacetate. The results are similar or even better than those obtained with the similar homogeneous systems, and the catalysts can be easily recovered and reused. The substitution in the methylene bridge leads to a slight reduction in the enantioselectivity and an unexpected cis-preference.     

聚合物支载噁唑类化合物在不对称反应中的应用

聚合物支载噁唑类化合物主要包括聚合物支载噁唑烷酮﹑噁唑啉和硼杂噁唑啉等, 其在不对称反应中主要用作手性助剂﹑手性催化剂及催化剂配体. 由于其便于分离提纯﹑可以回收重复使用且立体选择性没有明显降低等优点在不对称反应中得到了广泛的应用. 综述了近年来聚合物支载的噁唑类化合物在不对称反应中的应用.     

聚合物支载噁唑类化合物在不对称反应中的应用

聚合物支载噁唑类化合物主要包括聚合物支载噁唑烷酮、噁唑啉和硼杂噁唑啉等,其在不对称反应中主要用作手性助剂、手性催化剂及催化剂配体.由于其便于分离提纯、可以回收重复使用且立体选择性没有明显降低等优点在不对称反应中得到了广泛的应用.综述了近年来聚合物支载的噁唑类化合物在不对称反应中的应用     

Synthesis of non-symmetric bis(oxazoline)-containing ligands and their application in the catalytic enantioselective Nozaki-Hiyama-Kishi allylation of benzaldehyde

We report the good to high-yielding three-step synthesis of non-symmetrical bis(oxazoline)-containing ligands possessing an N-thienylaniline unit. The convergent synthesis employed a palladium-catalysed aryl amination of 2-(2'-bromothiophene)nitrile as the key step, with sixteen ligands prepared in total. These ligands were subsequently applied in the chromium-catalysed enantioselective Nozaki-Hiyama-Kishi allylation of benzaldehyde with an optimal enantioselectivity of 73%.     

Monomeric cobalt oxazoline palladacycles (COP). Useful catalysts for catalytic asymmetric rearrangement of allylic trichloroacetimidates

Cobalt oxazoline palladacycles (COP) containing acetylacetonate and hexafluoroacetylacetonate ligands were prepared as catalysts for the asymmetric rearrangement of allylic trichloroacetimidates. These monomeric catalysts are more soluble than the previously described chloride-bridged dimer COP-Cl (1). COP-hfacac (2) provides rearranged allylic trichloroacetamides with high enantiomeric purities (91-98% ee) in solvents of widely varying polarities: cyclohexane, toluene, 1,2-dichloroethane, ethyl acetate, acetone, acetonitrile, and THF. The first single-crystal X-ray structure of a COP catalyst is also reported.     

Polymer-supported pd(II) wacker-type catalysts

Seven polymer-supported Pd(II) catalysts have been prepared employing polymers carrying nitrile (cyanomethyl) ligands. Five of these involve polybenzimidazole backbones, one a polystyrene skeleton and the last a polyacrylonitrile backbone. The supported complexes have been used with CuCl₂ co-catalyst to oxidise dec-1-ene primarily to the methylketone under normal Wacker oxidation conditions. In some instances the supported complexes are more active than the (CH₃CN)₂PdCl₂ model. The most active species is a highly rigid - cyanomethylated polybenzimidazole and at least some of these metal centres may be coordinatively unsaturated. This catalyst also displays remarkable thermo-oxidative stability up to ∼400°C. The effect of solvent, temperature and co-catalyst ratio have been examined. The polymer-supported species remain very active at high temperature (∼120°C) and require addition of no hydrochloric acid to avoid irreversible precipitation of Pd(O) species. This is a complete contrast to homogeneous PdCl₂ which is rapidly deactivated under similar conditions with copious Pd black formation. Pd(O) complexes immobilised on the polymer seem to be “site isolated” and unable to aggregate. Re-oxidation therefore remains facile. The polymer-supported species have been recycled seven times. An initial fall in activity levels after 3 cycles and thereafter remains essentially constant. Appreciable Pd leaching also occurs in the first reaction but is rapidly arrested. After ∼6 cycles Pd loss is only ∼1 ppm per cycle. Following use of CuCl₂ co-catalyst in the first cycle, no additional Cu(II) needs to be added, and sufficient co-catalyst appears to be carried through with the isolated polymer-supported Pd(II) species. Starting with alk-1-enes isomerisation to the more thermodynamically stable internal alkenes is very much faster than oxidation. Indeed after only a short time no alk-1-ene is detectable e.g. by nuclear magnetic resonance analysis. Almost certainly, however, traces of the alk-1-ene do exist in equilibrium. Irrespective of whether the starting alkene is oct-1-ene, t-oct-2-ene or t-oct-4-ene the same three products are obtained: octan-2-one, -3-one and -4-one. In the case of oct-1-ene and t-oct-2-ene the composition of the ketone product mixture is very similar, although with t-oct-4-ene a significant increase in the proportion of the 4-one is observed. The major product in all cases however in the 2-one. The latter almost certainly arises from rapid oxidation of a small stationary concentration of alk-1-ene, with shift of the alkene equilibria maintaining the latter. Direct oxidation of the higher alkenes to the higher ketones occurs more slowly, but contrary to other reports in the literature this is significant.     

A novel bifunctional Ti(IV) complex catalyzed asymmetric silylcyanation of aldehydes

A novel Lewis acid and Lewis base bifunctional Ti(IV) complex was formed in situ upon the treatment of ligand (R)‐3,3′‐bis(diphenylphosphinoyl)‐BINOL with Ti(PrO‐i)₄, which is proven to be an efficient catalyst in the asymmetric trimethylsilylcyanation of aldehydes. The corresponding cyanohydrins were obtained in high to excellent chemical yield (83–93%) albeit with moderate enantioselectivities (up to 51% enantiomeric excess). © 2010 Wiley Periodicals, Inc. Heteroatom Chem 22:31–35, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20652     

Improved synthesis of aza-bis(oxazoline) ligands

A straightforward synthesis of chiral aza-bis(oxazoline) (Azabox) ligands from commercially available amino alcohols is described. The new protocol allows access to previously reported Azabox ligands in considerably improved yields but also to new derivatives, including non-C2-symmetrical ones.     

Polymer-supported catalysts in nucleophilic addition of n-butanol to isocyanates

The kinetics of n-butanol addition to isocyanate in the presence of organotin compounds and their polymer-supported analogues has been investigated. The functionalized polymer chain creates steric hindrances to the formation of non-reactive complexes which include organotin sites. The catalytic activity increases by a factor of 10–100 as compared with low molecular weight analogues.     

C2对称的类卟啉手性双噁唑啉的合成及其应用

合成了6个具有C2对称性的类卟啉手性双(口恶)唑啉配体,将这些化合物与RuCl3配位,NaIO4作氧化剂,应用于反式1,2-二苯基乙烯的不对称环氧化反应,获得了较高的产率(46.0%),但ee值(6.3%)较低.     

Convenient Synthesis of Bis（oxazoline） Dicarboxylate Derivatives

The synthesis of bis(oxazoline) dicarboxylate derivatives was investigated.Diethyl-aminosulfur trifluoride (DAST) was used as a convenient cyclization reagent in the synthesis of bis(oxazoline) dicarboxylate derivatives,which can not be obtained by the general method using MsC1 and Et3N as dehydrating cyclization reagent.     

Polymer-supported ionic-liquid-like phases (SILLPs): transferring ionic liquid properties to polymeric matrices

The physico-chemical properties of polymers with ionic-liquid-like moieties covalently bound to their surfaces (SILLPs) have been studied by thermal and spectroscopic techniques, as well as by direct impedance and dielectric measurements, and compared to those of the corresponding bulk ionic liquids. The effective transfer of properties from ionic liquids in solution to the supported species has thereby been demonstrated. The effects of the chemical nature of these tunable "solid solvents" on their macroscopic swelling and microwave heating, as well as the stabilities and activities of different catalytic moieties immobilized on the SILLPs, have been studied. Finally, the experimental effect observed in microwave heating can be directly correlated with the values of tan δ derived from dielectric measurements.     

Polymer-supported stereoselective synthesis of benzimidazolinopiperazinones

We describe the efficient synthesis of 4,7,8,10-tetrasubstituted-(((4S,10aS)-3-oxo-3,4,10,10a-tetrahydrobenzo[4,5]imidazo[1,2-a]pyrazin-2(1H)-yl)alkyl)amides on solid phase via tandem N-acyliminium ion cyclization-nucleophilic addition reactions. The synthesis proceeded with complete stereocontrol of a newly formed stereogenic center, provided crude material of high purity, and used commercially available building blocks under mild reaction conditions.     

Polymer-supported synthesis of mono-substituted porphyrins

Anchoring of substituted benzaldehydes to soluble and insoluble polymers allows for the synthesis of mono-substituted tetraarylporphyrins without the production of di-, tri-, and tetra-substituted porphyrin side products. The exclusion of the aforementioned side products during the synthesis of mono-substituted tetraarylporphyrin acids greatly reduced the complexity during purification of the product.     

Polymer-supported syntheses of cyclic oligodepsipeptides

A simple PS cyclization-cleavage method is described for the small-scale synthesis of cyclic oligodepsipeptides with 15 to 27 ring atoms per repeat unit. In selected cases, the cyclic monomers were isolated and characterized. If the cyclic oligomers are needed for the preparation of static or dynamic combinatorial libraries of macrocycles or for entropically-driven ring-opening polymerizations, all members of the family of macrocyclic oligomers are of interest as they all react through equilibration to give the same products.     

Solubility and miscibility of poly(ethyl oxazoline)

The solubility of poly(ethyl oxazoline) in aqueous solutions was studied. The cloud point temperatures decreased in the presence of sodium chloride but increased by the addition of tetrabutylammonium bromide or dioxane. Solution-cast films of blends of the polymer and poly(acrylic acid) were miscible, but mutual precipitation occurred in water, methanol, and dioxane. The compositions of the complexes correspond in most cases to simple molar ratios of the interacting groups. The glass transition temperatures of the complexes are higher than the values for blends of the same compositions, and the high values are attributed to hydrogen bonds acting as physical crosslinks. Complex formation also occurs when the polymer is mixed with a styrene-acrylic acid copolymer and with low weight polymers containing phenol groups.