Cyclic ethers, catalytic

It was noted early by Smid and his coworkers that open-chained polyethylene glycol type compounds bind alkali metals much as the crowns do, but with considerably lower binding constants. This suggested that such materials could be substituted for crown ethers in phase transfer catalytic reactions where a larger amount of the more economical material could effect the transformation just as effectively as more expensive cyclic ethers. Knbchel and coworkers demonstrated the application of open-chained crown ether equivalents in 1975 . Recently, a number of applications have been published in which simple polyethylene glycols are substituted for crowns . These include nucleophilic substitution reactions, as well as solubilization of arenediazonium cations . Glymes have also been bound into polymer backbones for use as catalysts " " . 

The reaction described is of considerable general utility for the preparation of benzoyloxy derivatives of unsaturated hydrocarbons.2"8 Reactions of 2-butyl perbenzoate with various other classes of compounds in the presence of catalytic amounts of copper ions produce benzoyloxy derivatives. Thus this reaction can also be used to effect one-step oxidation of saturated hydrocarbons,9, 10 esters,6,11 dialkyl and aryl alkyl ethers,12 14 benzylic ethers,11,15 cyclic ethers,13,16 straight-chain and benzylic sulfides,12, 17-19 cyclic sulfides,11,19 amides,11 and certain organo-silicon compounds.20... 

The oxidation of both linear and cyclic ethers to the corresponding acids and lactones by aqueous H202 as catalyzed by TS-1 and TS-2 was reported by Sasidharan et al. (241) (Scheme 17 and Table XXXV). The titanosilicates exhibited significantly better activity (about 55% conversion) and selectivity (98%) than chromium silicates, although vanadium silicates totally failed to catalyze the reaction. Such conversions are usually accomplished using either stoichiometric amounts of chromium trioxide, lead tetraacetate, or ruthenium tetroxide as oxidants (242) or catalytic amounts of Ru04 in the presence of... 

Considerable effort has been carried out by different groups in the preparation of amphiphihc block copolymers based on polyfethylene oxide) PEO and an ahphatic polyester. A common approach relies upon the use of preformed co- hydroxy PEO as macroinitiator precursors [51, 70]. Actually, the anionic ROP of ethylene oxide is readily initiated by alcohol molecules activated by potassium hydroxide in catalytic amounts. The equimolar reaction of the PEO hydroxy end group (s) with triethyl aluminum yields a macroinitiator that, according to the coordination-insertion mechanism previously discussed (see Sect. 2.1), is highly active in the eCL and LA polymerization. This strategy allows one to prepare di- or triblock copolymers depending on the functionality of the PEO macroinitiator (Scheme 13a,b). Diblock copolymers have also been successfully prepared by sequential addition of the cyclic ether (EO) and lactone monomers using tetraphenylporphynato aluminum alkoxides or chloride as the initiator [69]. 

Oxidation of cyclic ethers to lactones (1, 988). A systematic study of this reaction has been reported. In general, yields are good to excellent by either stoichiometric or catalytic procedures. No anhydrides from further oxidation are detected. The oxidation is chemoselective. Oxidation of a secondary position takes precedence over oxidation of a tertiary site. Primary positions are attacked in preference to secondary positions in the oxidation of acyclic ethers.1... 

In the past few years the use of aluminum alkyls as catalysts for cyclic ether polymerizations has received much attention. Two different mechanisms have been proposed to explain the catalytic activity of the aluminum alkyl catalysts. Saegusa, Imai, and Furukawa (75) suggest that a cationic mechanism is produced. They feel it is not related to the coordinate anionic mechanism presumed to take place with related catalyst systems used for aldehydes and epoxides. They propose that the Lewis acid first reacts with adventitious water to form a Bronsted acid. ... 

A series of functionalized alkenes has been subjected to selective epoxidation reactions. Oxidation of perfluorinated vinyl polyethers by bubbling oxygen through the liquid that contains a catalytic amount of a Lewis acid, e.g. antimony(V) fluoride, results in the formation of acid fluorides together with a smaller amount of C = C bond cleavage.76 Perfluorinated pentaaIkyI-2.3-dihydrofuran 38, an example of an unsaturated cyclic ether that is quite stable owing to perfluoroalkylation. is epoxidized by hypochlorite to the product 39 at 45 C.62... 

One of the most remarkable reactions performed by ruthenium-oxo complexes is the selective oxidation of aliphatic and cyclic ethers to the corresponding esters and lactones, respectively, with high yields under mild conditions.288,334 For example, tetrahydrofuran is oxidized by Ru04 to y-butyrolactone with nearly quantitative yields.334 A catalytic reaction can be carried out in the presence of excess hypochlorite or periodate.332,335... 

In this chapter, some of the essential aspects of the synthesis and characterization of copolymers derived from the coupling of C02 with various monomers, namely, epoxides, oxetanes, and aziridines, have been reviewed. In addition, the use of carbon disulfide as a resource for copolymer production was introduced, and the present understanding of the mechanistic aspects of processes involving cyclic ethers and C02 catalyzed by well-defined metal systems has been emphasized. This knowledge has led to the development of catalytic systems capable of controlling not only the product selectivity but also the regio- and stereoregularities of the resultant copolymers. 

Fem and Mn11 bpy complexes in zeolite Y and bentonite, were shown to have catalytic potential in the oxidation of cyclic ethers with peroxides to yield cyclic lactols [99]... 

Various cycloalkanones were converted to rearranged cyclic ethers in the presence of a catalytic amount of hydrogen fluoride in 16-18% yield, while increasing the amount of hydrogen fluoride resulted in a higher conversion of starting ketone, but the ethers were further fluorinated on the aromatic ring23,24,107. 

Unsymmetrical alkyl phenyl tellurium derivatives were prepared in good yields from phenyl trimethylsilyl tellurium and epoxides, carboxylic acid esters, and linear or cyclic ethers under very mild conditions. In these reactions, which proceed in dichloromethane in the presence of a catalytic amount of zinc iodide, a carbon-oxygen single bond is cleaved. The highly nucleophilic benzenetellurolate binds to the carbon fragment, whereas the trimethylsilyl group becomes linked to the oxygen. 

Cyclic ethers and amines can be formed if the nucleophile is an intramolecular alcohol or amine. Stoichiometric palladium can be avoided by using benzoquinone as the stoichiometric oxidant with a catalytic amount of palladium. In this example intramolecular oxypalladation of a diene is followed by attack of an external nucleophile on a TC-allyl complex. 

The dialkylzinc compounds are extremely moisture sensitive and even react explosively with bulk water. Nevertheless, cryoscopic studies carried out on the controlled hydrolysis of diethylzinc show the formation of organozinc hydroxide EtZnOH as intermediate. This intermediate, which is thought to have the dimeric structure (EtZnOH)2, is very unstable and reacts further to give polymers of the form Et(ZnO) (equation 19). Some of these products exhibit a good catalytic activity for the polymerization of lactones and cyclic ethers. 

Catalytic reactions with hydrosilanes and carbon monoxide. The reactions of olefins, cyclic ethers, and aldehydes with a hydrosilane and carbon monoxide catalyzed by Co2(CO)k or Ru or Rh complexes have been reviewed (48... 

Tri(organoseleno)boranes 35 are prepared from boron trihalides and organic selenolates as stable compounds (Scheme 35) [63]. These selenoboranes have been shown to be useful for the conversion of carbonyl compounds into seleno-acetals 36 [64] and the selective ring opening of epoxides [65]. Recently, it was reported that tri(phenylseleno)borane reacts with cyclic ethers to produce m-hydroxyalkyl phenyl selenides 37 in the presence of a catalytic amount of Lewis acid [43]. 

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