With acyclic ethers

With acyclic ethers. In a study of THF polymerization using PFjT gegenions Dreyfuss (25) show that in the presence of dialkyl ethers chain transfer occurs and continues to occur after equilibrium is reached. The ultimate conversion to polymer is not affected but the intrinsic viscosity of the polymer decreases with time (Fig. 6). The reaction involved is essentially the reverse of the initiation reaction with trialkyl oxonium salts (equation 5). In the case of transfer the dialkyl ether reacts with the propagating oxonium ion to give a trialkyl oxonium ion which has one long chain alkyl and two short alkyls derived from the ether. 

Attack by THF on one of the alpha carbons of the short alkyl groups completes the chain transfer process  

If a cyclic ether such as dioxolane or dioxane is substituted for the acyclic ether the result is copolymerization of the cyclic ether (25) (Fig. 6). 

Sims (40) obtained further evidence for transfer with diethylether by using Cu labeled ether as solvent. He showed that the activity of the polymer increased with time (Table 7). 

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Large-ring heterocyclic radicals are not particularly well known as a class. Their behavior often resembles that of their acyclic counterparts, except for transannular reactions, such as the intramolecular hydrogen transfer in 1-azacyclononan-1-yl 1 (Scheme 1). As is the case with acyclic ethers, oxepane in the reaction with tert-butoxy radical suffers abstraction of a hydrogen atom from the 2-position in the first reaction step (Scheme 2). 

Similar improvements have been reported by Ewin and Simpkins for the asymmetric deprotonation of cyclic ether complexes and subsequent quenching with benzophenone (Scheme 48)80,89. Interestingly, switching from the monoamide (R,R)-3 to the bisamide (R,S,S,R)-67 resulted in increased ee from 75% to 99% and, as with acyclic ether complexes, the absolute configurations of the products were different. 

Bilirubin [635-65-4] M 584.7, e450nm t OO in CHCI3, pKE t 3 0. An acyclic tetrapyrrole bile pigment with impurities which can be eliminated by successive Soxhiet extraction with diethyl ether and MeOH. It crystallises from CHCI3 as deep red-brown rhombs, plates or prisms, and is dried to constant weight at 80 under vacuum, [Gray et al. J Chem Soc 2264, 2276 1961.]... 

The reactions of nitrones constitute the absolute majority of metal-catalyzed asymmetric 1,3-dipolar cycloaddition reactions. Boron, aluminum, titanium, copper and palladium catalysts have been tested for the inverse electron-demand 1,3-dipolar cycloaddition reaction of nitrones with electron-rich alkenes. Fair enantioselectivities of up to 79% ee were obtained with oxazaborolidinone catalysts. However, the AlMe-3,3 -Ar-BINOL complexes proved to be superior for reactions of both acyclic and cyclic nitrones and more than >99% ee was obtained in some reactions. The Cu(OTf)2-BOX catalyst was efficient for reactions of the glyoxylate-derived nitrones with vinyl ethers and enantioselectivities of up to 93% ee were obtained. 

The rearrangement with ring contraction probably is the most important synthetic application of the Favorskii reaction it is for example used in the synthesis of steroids. Yields can vary from good to moderate. As solvents diethyl ether or alcohols are often used. With acyclic a-halo ketones bearing voluminous substituents in a -position, yields can be low a tcrt-butyl substituent will prevent the rearrangement. 

Kuokkanen evaluated a series of constants. Kpeg for substituted diazonium ions with PEG 1000 and found a reaction constant (p = 1.12) comparable to those for complexation with the three crown ethers investigated by Nakazumi et al. (1983), p = 1.18-1.38). It is therefore likely that the host-guest interaction of diazonium ions with acyclic polyethers is basically similar to that with crown ethers. A dual substituent parameter analysis (DSP, see Sec. 8.3) for (Nakazumi et al., 1987)... 

The addition of sulphinyl chlorides to trimethylsilyl enol ether 138 affording a-ketosulphoxides 139 (equation 76) represents an extension of the reaction of sulphinyl chlorides with ketones. This reaction has attracted attention only recently. Sergeev and coworkers192 reported that treatment of sulphinyl chlorides with acyclic enol ethers afforded a-ketosulphoxides 139 in good to excellent yields. Meanwell and Johnson193 observed that in the case of cyclic enol ethers the corresponding sulphoxides were formed only in very low yields. They found, however, that the introduction of an equivalent amount of a Lewis acid into the reaction mixture markedly promotes the desired reaction, whereas the use of catalytic amounts of a Lewis acid led to a substantial reduction in the yield. This is most probably due to the formation of a complex, between the a-ketosulphoxide and the Lewis acid. 

Markies et al. have studied the coordination of zinc to cyclic and acyclic polyether ligands. In some cases the zinc is not coordinated within the ligand cavity but only through two of the ether donors in the macrocyclic ring.360 The bis(methoxyethyl)ether complex of zinc diphenyl (41) is five-coordinate with three ether oxygens coordinating from the acyclic ligand.361... 

Falbe and Korte (90) studied the cobalt hydroformylation of dihydro-pyran and its derivatives. The reactions were conducted at temperatures above 180°C, with pressures of 300 atm of 1/1 H2/CO. Under these conditions, the initially formed aldehydes were hydrogenated to the alcohols in situ. As noted with acyclic vinyl ethers, formyl attachment was predominantly a. 

Jorgensen s group44a carried out the reaction using the anhydrous form of chiral bis(oxazoline) coordinated copper complex. Complex 106 containing 83 as the chiral ligand was found to be the most effective. As shown in Scheme 5-32, the asymmetric hetero Diels-Alder reaction of //.y-unsaturated a-keto esters with acyclic enol ethers results in products with excellent yield and enantioselectivity. 

A semiempirical AMI study of the inverse-electron-demand Diels-Alder reaction of 4-substituted 6-nitrobenzofurans with enol ethers and enamines favours a stepwise mechanism involving short-lived diradical intermediates. The inverse-electron-demand intermolecular Diels-Alder reactions of 3,6-bis(trifluoromethyl)-l,2,4,5-tetra-zine with acyclic and cyclic dienophiles followed by the elimination of N2 produce 4,5-dihydropyridazines, which cycloadd further to yield cage compounds. The preparation of jS-carbolines (90) via an intramolecular inverse-electron-demand Diels-Alder... 

Acyclic ethers undergo partial j8-scission with formation of carbonyl and alkyl derivatives. Thus with ethyl ether the introduction of the oxyalkyl group is accompanied by appreciable quantities of ethyl and acetyl derivatives, attributed to jS-scission of the a-oxyalkyl radical [Eq. (47)]. 

Dreyfuss and Dreyfuss reasoned that a similar chain transfer should also occur with added small acyclic ethers. Indeed in the presence of diethyl ether they found that the ultimate conversion of THF to polymer was not affected but that the intrinsic viscosity of the polymer decreased with time (20). ... 

Benzyl-alkyl, dialkyl, cyclic and acyclic ethers were converted to esters or lactones by RuO or [RuO ] (RuClj/aq. Na(C10) or Ca(C10)j/CH2Cl2). It was not stated whether RuO or [RuO ] was the effective oxidant, but oxidation of jb-methoxy-benzyhnethyl ether apparently involved a one-electron transfer process, which might be more likely to occur with [RuO ] [426],... 

A very useful class of chiral auxiliaries has been developed for alkenes substituted with a heteroatom. These auxiliaries, attached to the heteroatom, allow for the preparation of enantiomerically enriched cyclopropanols, cyclopropylamines and cyclopropylboronic acids. Tai and coworkers have developed a method to efficiently generate substituted cyclopropanol derivatives using the cyclopropanation of a chiral enol ether (equation 78) . The reaction proceeds with very high diastereocontrol with five- to eight-membered ring sizes as well as with acyclic enol ethers. The potential problem with the latter is the control of the double bond geometry upon enol ether formation. A detailed mechanistic study involving two zinc centers in the transition structure has been reported. ... 

Distal C-C bond formation can also be used to construct cyclic ethers, but this demands that methods be developed for the enantioselective assembly of complex acyclic ethers. P. Andrew Evans of Indiana University has demonstrated (Angew. Chem. Jnt. Ed. 2004, 43,4788) that Rh-mediated coupling of secondary allylic carbonates such as 7 with secondary alcohols such as 8, both enantiomerically pure, proceeds with clean retention (double inversion) of absolute configuration. Alkene metathesis then delivers the cyclic ether 9 in high diastereomeric and enantiomeric purity. 

Boron trifluoride-diethyl ether complex also proved to be useful with acyclic epoxides.34... 

Multidentate ligands, both acyclic and cyclic, are now abundant and herein the nomenclature used will follow that recently proposed by Vogtle and Weber.33 Coronands are taken to mean macromonocyclic compounds having any heteroatoms present as potential donors, with crown ethers being reserved for compounds of the same type having only oxygen atoms present as... 

The UV photoelectron spectra of several chromans have been compared with other cyclic and acyclic ethers. The chroman spectra are clearly distinguishable from those of the other ethers and the differences have been interpreted in terms of the decreased conjugative effects of oxygen and increased hyperconjugative effects of the 4-methylene group (76T167). 

The same cleavage is observed with acyclic homoallyl ethers. Example ... 

P,Y-Unsaturated ketones.1 The reaction of acyclic a,p-epoxy ketones with two equivalents of 1 results in the cyclopropanols 2, which are converted into p,Y-enones on treatment with BF3 etherate or HC1. 

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