Etherification reaction conditions

The symmetrical dimers can be synthesized either in a single step by reacting the monohydroxy-TP with 0.5 equivalent of the appropriate a, co-dibromoalkane under classical etherification reaction conditions or in two steps. In the two-step procedure, the monohydroxy-pentaalkoxy-TP is first reacted with an excess of the appropriate... 

After identifying the optimal etherification conditions, our attention turned to isolation of 18 in diastereomerically pure form. Diastereomers 18 and 19 were not crystalline, but, fortunately, the corresponding carboxylic acid 71 was crystalline. Saponification of the crude etherification reaction mixture of 18 and 19 with NaOH in MeOH resulted in the quantitative formation of carboxylic acids 71 and 72 (17 1) (Scheme 7.22). Since the etherification reaction only proceeded to 75-80% conversion, there still remained starting alcohol 10. Unfortunately, all attempts to fractionally crystallize the desired diastereomer 71 from the crude mixture proved unfruitful. It was reasoned that crystallization and purification of 71 would be possible via an appropriate salt. A screen of a variety of amines was then undertaken. During the screening process it was discovered that when NEt3 was added... 

The etherification between alcohol 10 and imidate 67 was one of the key transformations in the successful preparation of compound 1. The use of HBF4 as the catalyst for the etherification was crucial for obtaining high levels of diastereose-lectivity and relatively high conversion to the desired product 18. The fact that sec-sec ethers have rarely, if ever, been obtained with high levels of diastereocontrol in Sn2 fashion under typical SN1 reaction conditions prompted us to investigate the complex mechanistic details of this exceptional reaction. 

Table 7.1 Etherification reaction profile under optimized conditions.

PECH was modified under similar reaction conditions, except that dimethylformamide (DMF) was used as the reaction solvent. In addition, the phase-transfer-catalyzed etherification of the chloromethyl groups of PECH with sodium 4-methoxy -4 -biphenoxide was used to synthesize PECH with direct attachment of the mesogen to the polymer backbone. Similar notations to those used to describe the functionalized PPO are used for functionalized PECH. In this last case, PPO was replaced with PECH. Esterification routes of both PPO and PECH are presented in Scheme I. 

A heterobimetallic BINOL-Ga/Li complex 53 has been developed for the enantioselective ARO of meso-cpoxides (BINOL = l,T-bi(2-naphthol)).278 Using />-methoxyphenol as the nucleophile, this etherification reaction was observed to take place with a high level of asymmetric induction. An improved catalyst 54 has also been reported that exhibits greater stability under the reaction conditions and delivers higher yields and ee s (Equation (78)).279 A simple catalyst derived from Sc(OTf)3 and the chiral bipyridine ligand 52 has been shown to be effective for the ARO of aryl-substituted /// -epoxides with aliphatic alcohols to give high ee s (Equation (79)).280... 

The vapour pressures of the main volatile compounds involved in esterification and polycondensation are summarized in Figure 2.25. Besides EG and water, these are the etherification products DEG and dioxane, together with acetaldehyde as the main volatile product of thermal PET degradation. Acetaldehyde, water and dioxane all possess a high vapour pressure and diffuse rapidly, and so will evaporate quickly under reaction conditions. EG and DEG have lower vapour pressures but will still evaporate from the reaction mixture easily. 

The major difference between our reaction conditions and the conventional phase transfer catalyzed Williamson etherification (22) is the use of stoichiometric amounts of phase transfer catalyst versus the nucleophilic chain ends in the former case. Under these... 

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. 

The reaction of acceptor-substituted carbene complexes with alcohols to yield ethers is a valuable alternative to other etherification reactions [1152,1209-1211], This reaction generally proceeds faster than cyclopropanation [1176], As in other transformations with electrophilic carbene complexes, the reaction conditions are mild and well-suited to base- or acid-sensitive substrates [1212], As an illustrative example, Experimental Procedure 4.2.4 describes the carbene-mediated etherification of a serine derivative. This type of substrate is very difficult to etherify under basic conditions (e.g. NaH, alkyl halide [1213]), because of an intramolecular hydrogen-bond between the nitrogen-bound hydrogen and the hydroxy group. Further, upon treatment with bases serine ethers readily eliminate alkoxide to give acrylates. With the aid of electrophilic carbene complexes, however, acceptable yields of 0-alkylated serine derivatives can be obtained. 

Most acid-labile benzyl alcohol linkers suitable for the attachment of carboxylic acids to insoluble supports can also be used to attach aliphatic or aromatic alcohols as ethers. The attachment of alcohols as ethers is less easily accomplished than esterification, and might require the use of strong bases (Williamson ether synthesis [395,552,553]) or acids. These harsh reaction conditions limit the range of additional functional groups that may be present in the alcohol. Some suitable etherification strategies are outlined in Figure 3.31. Etherifications are treated in detail in Section 7.2. 

Less problematic are etherifications with epoxides under acidic reaction conditions. Although we would expect the nucleophile to attack the position which most easily forms a carbocahon, this does not always happen and steric effects also seem to be important (Scheme 4.79). 

Cellulose ethers generally are very stable. Many etherified cottons are highly resistant to hydrolytic removal of substituent groups under both acidic and alkaline conditions. Because of this stability, many of the most practical chemical treatments of cotton are based on etherification reactions [9,328-331]. These treatments provide cotton products with useful, durable properties including wrinkle resistance, water repellency, flame resistance, and antimicrobial action. 

Several electroi ilic selenium-induced cyclizations are known. Th include etherifications, lactoni-zations and lactamidation. Some reasons why selenium electro riiiles are used extensively in cyclizations include consistently good yields, few by-pn cts and mild reaction conditions, as well as the abili to further manipulate the seleno group in a variety of straightforward fashions. 

Scheme 2. Phenylselenyl groups are stable to many classical reaction conditions (organo-lithium, etherification, Pauson-Khand reaction)...

Amorphous Sn-, Si-, and Al-containing mixed oxides with homogeneous elemental distribution, elemental domains, and well-characterized pore architecture, including micropores and mesopores, can be prepared under controlled conditions by use of two different sol-gel processes. Sn-Si mixed oxides with low Sn content are very active and selective mild acid catalysts which are useful for esterification and etherification reactions [121]. These materials have large surface areas, and their catalytic activity and selectivity are excellent. In the esterification reaction of pentaerythritol and stearic acid catalytic activity can be correlated with surface area and decreasing tin content. The trend of decreasing tin content points to the potential importance of isolated Sn centers as active sites. 

The relative rates of olefin production and etherification have been shown to vary with reaction conditions (99-101), including temperature and contact time, and with the geometry of the catalyst pore system (99). Bryant (99) has demonstrated kinetic effects in ethanol and n-butanol dehydration that greatly favor olefin formation using a series... 

Typical etherification process conditions are (i) liquid phase (p<18bar), (ii) temperature <100°C and (iii) use of a strong cation-exchange resins as catalysts. It is an exothermic reactions with thermodynamic limitations. 

Type of reaction C-O bond formation Reaction condition solid-state Keywords alcohol, TsOH, etherification, ether... 

As shown in the following scheme, a SEM-ether derived phenyl acetylene was treated with PtClj in the presence of CO to give a benzo[4>]furan, which was first subjected to desilylation, followed by Pd-catalyzed intramolecular etherification, affording the tetracyclic skeleton of pterocarpane family of phytoalexins <05JA15024>. A similar type of synthetic transformation was so applied to make a key intermediate in the total synthesis of vibsanol <05JA15022>. 2,3-Disubstituted benzo[h]furans were prepared under very mild reaction conditions by the Pd/Cu-catalyzed cross-coupling of various o-iodoanisoles and terminal... 

For the selective W-alkylation of nucleotides, reagents and reaction conditions must be chosen carefully, in order to avoid etherification of... 

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