Polyethers synthesis procedure

There are various procedures for the preparation of polyethers. These procedures typically start with oxirane or oxirane derivatives (e.g. propylene oxide, etc.). Base catalyzed anionic polymerization, acid initiation, or complex coordination catalysis can be used for the reaction [1-3], Not only oxiranes can generate polyethers. Diols also can be used for polyether synthesis. Other source compounds include tetrahydrofuran, which can be polymerized to a polyether using fluorosulfonic acid (HSO3F) as a catalyst, oxetane (trimethylene oxide) or oxetane derivatives, which can be polymerized to generate polyethers with practical applications such as poly[bis(chloromethyl)oxetane], etc. 

The compound known as 18-crown-6 is one of the simplest and most useful of the macrocyclic polyethers. Its synthesis in low yield was first reported by Pedersen. Greene and Dale and Kristiansen" have reported syntheses of the title compound from triethylene glycol and triethylene glycol di-p-toluenesulfonate. Both of these procedures use strong base and anhydrous conditions and achieve purification by more or leas classical methods. The combination of distillation and formation of the acetonitrile complex affords crown of high purity without lengthy chromatography or sublimation. ... 

Similar 5-exo cyclization procedures have been widely utilized by Evans in his total syntheses of complex natural compounds, such as the synthesis of ionomycin [12a] and polyether antibiotic X-206 [12b]. A 5-exo cyclization of a y-epoxy alcohol has also been observed under basic conditions [12c]. 

A reiterative application of a two-carbon elongation reaction of a chiral carbonyl compound (Homer-Emmonds reaction), reduction (DIBAL) of the obtained trans unsaturated ester, asymmetric epoxidation (SAE or MCPBA) of the resulting allylic alcohol, and then C-2 regioselective addition of a cuprate (Me2CuLi) to the corresponding chiral epoxy alcohol has been utilized for the construction of the polypropionate-derived chain ]R-CH(Me)CH(OH)CH(Me)-R ], present as a partial structure in important natural products such as polyether, ansamycin, or macro-lide antibiotics [52]. A seminal application of this procedure is offered by Kishi s synthesis of the C19-C26 polyketide-type aliphatic segment of rifamycin S, starting from aldehyde 105 (Scheme 8.29) [53]. 

The efficacy of the procedure for the synthesis of highly complex systems, and the utility of the enol ether functionality obtained in the reaction is demonstrated by the conversion of the intricate polyether 134 to enol ether 135 and its subsequent elaboration to the hexacyclic system 138 (Scheme 20) [34a]. 

An example for the synthesis of poly(2,6-dimethyl-l,4-phenylene oxide) - aromatic poly(ether-sulfone) - poly(2,6-dimethyl-1,4-pheny-lene oxide) ABA triblock copolymer is presented in Scheme 6. Quantitative etherification of the two polymer chain ends has been accomplished under mild reaction conditions detailed elsewhere(11). Figure 4 presents the 200 MHz Ir-NMR spectra of the co-(2,6-dimethyl-phenol) poly(2,6-dimethyl-l,4-phenylene oxide), of the 01, w-di(chloroally) aromatic polyether sulfone and of the obtained ABA triblock copolymers as convincing evidence for the quantitative reaction of the parent pol3rmers chain ends. Additional evidence for the very clean synthetic procedure comes from the gel permeation chromatograms of the two starting oligomers and of the obtained ABA triblock copolymer presented in Figure 5. 

Chirality derived from the readily accessible a-amino acids has been incorporated into the side chains of aza and diaza macrocyclic polyethers. A number of procedures suitable for peptide synthesis have proved (178) to be unsuitable for acylating the relatively unreactive secondary amine groups of aza crown ethers. Eventually, it was discovered that mixed anhydrides of diphenylphos-phinic acid and alkoxycarbonyl-L-alanine derivatives do yield amides, which can be reduced to the corresponding amines, e.g., l-172. By contrast, the corresponding bisamides of diaza-15-crown-S derivatives could not be reduced and so an alternative approach, involving the use of chiral A-chloroacetamido alcohols derived from a-amino acids, has been employed (178) in the synthesis of chiral receptors, such as ll-173 to ll-175, based on this constitution. 

Hyperbranched polymers are formed by polymerization of AB,-monomers as first theoretically discussed by Flory. A wide variety of hyperbranched polymer structures such as aromatic polyethers and polyesters, aliphatic polyesters. polyphenylenes, and aromatic polyamides have been described in the literature. The structure of hyperbranched polymers allows some defects, i.e. the degree of branching (DB) is less than one. The synthesis of hyperbranched polymers can often be simplified compared to the one of dendrimers since it is not necessary to use protection/deprotection steps. The most common synthetic route follows a one-pot procedure " where AB,-monomers are condensated in the presence of a catalyst. Another method using a core molecule and an AB,-monomer has been described. ... 

An improved procedure for cyclopalladation-carbonylation (of e.g. 320) relies on the addition of CuCl and LiCl to the standard PdCl2-CuCl2 mixture. This indicates that both the Cu2+ and Cu+ are required in sufficient concentrations to keep up the cascade of the catalytic cycle. This method is superior to the Hg(II)-mediated cyclization followed by transmetallation with Pd in CO/MeOH197. For application in the synthesis of polyether antibiotics, see elsewhere435. 

Reductive cleavage of dioxepanes with borane-THF complex (THF = tetrahydrofuran) leads to 1,4-diols. This procedure has found application in the synthesis of discrete polyethers (Scheme 27) <2003JOC9166>. 

Because the procedure used in making these polymers is similar (10), it is sufficient to describe one, namely, the synthesis of the ter-polyether from bisphenol A, diphenolic acid, and dichlorodiphenyl sulfone, whose polymerization scheme is ... 

The Stoddart group has used the principles employed in their catenane studies to synthesise both a molecular trifoil knot and its isomeric large ring in very low yield. These isomers were separated by HPLC and characterised by liquid secondary ion mass spectrometry. The synthetic procedure, which is illustrated schematically in Figure 5.26, was based on the formation of a double-stranded supramolecular complex between an acyclic 7C-electron-rich, 1,5-dioxynaphthalene-based polyether and an acyclic 7i-electron-deficient bipyridinium-based tetracation. The extremely low efficiency of the synthesis in this case appears to reflect an unfavourable solution geometry of the intermediate host-guest complex - the latter... 

Polymer Synthesis. A typical polymerization procedure for the a, to-dibromoalkoxy polyethers of bis(4-hydroxyphenoxy)-p-xylene (HPX) is as follows To 7.5 ml of a... 

It has been shown that application of previously synthesized ethers of isosorbide was beneficial and enabled the preparation of polyethers in better yields than the polyethers obtained in direct reactions of isosorbide and dibromo or dimesyl alkanes [47, 48]. Moreover, the molecular weights of the polyethers were higher than of those prepared in the earlier work [47] and the molecular weight distributions of new polyethers were similar or lower. Such a microwave-assisted procedure can contribute to the synthesis of alternating polyethers and further modification of their properties. 

Synthesis of polyethers by polycondensation of alcohols can also be performed by the classical interfacial reaction between functionalized monomers. By this procedure, an organotin polyether was synthesized in a rapid (15 s) and high yield reaction (>80%) [26]. 

Two groups have reported on the use of the Claisen rearrangement to obtain 2,3-unsaturated C-glycosides. Fraser-Reid and colleagues found the standard reaction applied to derivatives of the allylic alcohol (77) inefficient because of the poor yields of the derived vinyl ethers or because allylic esters e.g. (78) predominated. They were successful, however, in obtaining compounds (79) and (80) by modified procedures (Scheme 5). An alternative synthesis of saturated, and hence unsaturated, C-glycosides was developed as illustrated in Scheme 6. In parallel work Ireland and co-workers used the enol silyl ether approach as shown in Scheme 7 and employed the products in polyether antibiotic syntheses. ... 

The experimental results on the synthesis and characterization of PHMS are summarized in Table 1. Only 1,2-dibromoethane did not produce any polymer, and comments on this result will be reserved until later. As we have speculated, all the obtained polyethers are soluble in organic solvents like o-dichlorobenzene, THF and CHCl (Table 1). These are conventional solvents for further functionalization of the a,o)-dielectrophilic oligomer s chain ends, or for the preparation of alternating or triblock copol3nners by phase transfer catalysed polyetherification. Conversely, the polyethers are not soluble in dipolar aprotlc solvents. As a result, conventional condensation polymerization reactions can not be used for their synthesis. The only available synthetic procedure to be used for their preparation is phase transfer catalyzed polyetherification. The polyethers containing an... 

In a program aimed at the total synthesis of polyether antibiotic monensin, Ireland et al. devised a procedure for the in situ silylation of an ester enolate with a j5-leaving group, first executed with the model substrate 165 (Scheme 32). When added to a premixed solution of LDA and TMSCl in 10% HMPA/THF at -100°C, crotyl ester 165 produced after rearrangement at room temperature, desilylation, and treatment with diazomethane, the diastereomeric Claisen products 166 a and 166 b in almost 80% combined yield [63]. The success of this three-component competition experiment depended on the relative rates of N-silylation vs. enolization and -elimination vs. 0-silylation, respectively, with all of these processes occurring on a subminute time scale at -100 C. 

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