Ethers, reactions table

The most convenient and successful synthetic preparation of octa-chlorodibenzo-p-dioxin has been described by Kulka (13). The procedure involves chlorination of pentachlorophenol in refluxing trichlorobenzene to give octachlorodibenzo-p-dioxin in 80% yield. Kulka has explained the reaction as coupling between two pentachlorophenoxy radicals. Large amounts (5—15%) of heptachlorodibenzo-p-dioxin were observed in the unpurified product. Since the pentachlorophenol used in this study contained 0.07% tetrachlorophenol, we feel that tetrachloro-phenol may be produced in situ (Reaction 4). Such a scheme would be analogous to the formation of 2,4-dichlorophenol and 3-chlorophenol produced from 2,4,4 -trichloro-2 -hydroxydiphenyl ether (Reaction 2). The solubility of octachlorodibenzo-p-dioxin was determined in various solvents data are presented in Table II. 

When the source of initiation is altered from ionising radiation to UV, analogous additive effects to those previously discussed have been found. For reasonable rates of reaction, sensitisers such as benzoin ethyl ether (B) are required in these UV processes. Thus inclusion of mineral acid or lithium perchlorate in the monomer solution leads to enhancement in the photografting of styrene in methanol to polyethylene or cellulose (Table V). Lithium nitrate is almost as effective as lithium perchlorate as salt additive in these reactions (Table VI), hence the salt additive effect is independent of the anion in this instance. When TMPTA is included with mineral acid in the monomer solution, synergistic effects with the photografting of styrene in methanol to polyethylene are observed (Table VII) consistent with the analogous ionising radiation system. 

Increasing the hydrophobicity of quaternary ammonium salts increases the apparent extraction constants for the ion pair and therefore leads to a higher catalytic activity (Brandstrom, 1977). The same phenomenon has been observed by Cinquini and Tundo (1976) for crown ether catalysis (Table 35). The catalytic activity of 18-crown-6 [3] and alkyl-substituted derivatives [117]—[ 119] in the reaction of n-CgH17Br with aqueous KI follows the order [117], [118] > [119] s> [3]. The alkyl-substituted [2.2]-cryptand derivatives are also much more efficient than the parent compound [86]. Increasing the hydrophobicity of [2.2.2]-cryptand (Cinquini et al., 1975) and even of polypode ligands (Fornasier et al., 1976) leads to higher catalytic activity. The tetradecyl-substituted compounds show the reactivity sequence [2.2.2]-cryptand at 18-crown-6 > [2.2]-cryptand on the reactivity scale that can be distilled from Table 35. 

Polymerizations were carried out using a number of bisphenols and bisthiophenols (7a-e) with HFB (see Scheme I) and with (4a-c) the bishaloaromatics (see Scheme II). Typically, solutions equimolar (ca. 2.5M) in comonomer were treated with excess anhydrous K2CO3 and 27.7 mole % of 18-crown-6 ether. Reactions were run in a number of different solvents and at temperatures from 55 to 80 . Our results showed that polymerizations were sensitive to PTC parameters such as solvent, catalyst, and trace amounts of water in the organic phase. Under optimized conditions the expected polymers were generally obtained in excellent yields and moderately high molecular weights as evidenced by ninh measurements (see Table I). 

Zhu and Burgess have reported an asymmetric conjugate reduction of 1,3-enol ether esters (Table 9) and 1,3-enol ether alcohols (Table 10) [72]. Initial reaction conditions reached full conversion of E-l-methoxy-l-phenylethene using ligand 9 albeit with a very low enantioselectivity of 29%. 

Table 2 contains the characteristics of the amic ester-aryl ether copolymers including coblock type, composition, and intrinsic viscosity. Three series of copolymers were prepared in which the aryl ether phenylquinoxaline [44], aryl ether benzoxazole [47], or aryl ether ether ketone oligomers [57-59] were co-re-acted with various compositions of ODA and PMDA diethyl ester diacyl chloride samples (2a-k). The aryl ether compositions varied from approximately 20 to 50 wt% (denoted 2a-d) so as to vary the structure of the microphase-separated morphology of the copolymer. The composition of aryl ether coblock in the copolymers, as determined by NMR, was similar to that calculated from the charge of the aryl ether coblock (Table 2). The viscosity measurements, also shown in Table 2, were high and comparable to that of a high molecular weight poly(amic ethyl ester) homopolymer. In some cases, a chloroform solvent rinse was required to remove aryl ether homopolymer contamination. It should also be pointed out that both the powder and solution forms of the poly(amic ethyl ester) copolymers are stable and do not undergo transamidization reactions or viscosity loss with time, unlike their poly(amic acid) analogs.

In order to obtain further insight into the mechanism of the Mannich-type reaction, sulfone IP and silyl enol ether derived from acetophenone were reacted in the presence HOTf or TMSOTf, which could be produced in the reaction medium when using Bi(0Tf)3-4H20 as catalyst. It appeared that these two compounds efficiently catalyze the Mannich-type reaction (Table 7, entries 2 and 3). The reaction does not occur in the presence of 2,6-di-/<7V-buty I-4-methyl-pyridine [DTBMP] (1.0 equiv. of lp, 1.3 equiv. of silyl enol ether, 0.5 mol% of Bi(0Tf)34H20, 1.5 mol% of 2,6-di-/c/V-buty l-4-methy I-pyridine, 22 °C, 20 h, 99% recovery of lp), which indicates that triflic acid is involved in the mechanism (Table 7, entry 4). 

Sorbitol (4) exhibits low reactivity, so a large excess of butadiene was used in the reaction (Table 3). Almost fully substituted sorbitol can be obtained using 1 M NaOH//-PrOH solvent for 3 days. At DS = 5, the resulting product was soluble in apolar solvents such as petroleum ether [20]. 

Table I shows the effects of Mel/DME and CO/DME ratios in the feed gas on product yields. With increasing Mel/DME ratio both methyl acetate yield and selectivity increased. The yield of methyl acetate increased with an increase in the CO/DME ratio whereas its selectivity decreased. In the case of methanol carbonylation on Ni/A.C. catalyst, the product yield and selectivity were strongly affected by CO/MeOH ratio but not by Mel/MeOH ratio (14-16). The promoting effect of methyl iodide on the methanol carbonylation reached a maximum at a very low partial pressure, that is 0.1 atm or lower. However, both CO/DME and Mel/DME ratios were important for regulating the product yield and selectivity of the dimethyl ether carbonylation. This suggests that the two steps, namely, the dissociative adsorption of methyl iodide on nickel (Equation 4) and the insertion of CO (Equation 5) are slow in the case of dimethyl ether reaction.

A BINOL-dimethylaminopyridine hybrid was seen to be efficient in mediating the MBH reaction (Table 5.14) [96], with optimal reaction conditions being found as —15 °C with a mixed solvent system consisting of toluene and cyclopentyl methyl ether (CPME) in a 1 9 ratio. The reaction was sensitive to the structure of the catalyst 112, the position of the Lewis base attached to BINOL, the substitution pattern of the amino group, and the length of the spacer. It should be noted that the bulky i-Pr substituent on the amino group showed the best selectivity and kinetic profile (Table 5.14, entry 5) [98]. (For experimental details see Chapter 14.10.4). 

Examples of the double hydroxylation reaction observed for several representative substrates illustrate the scope of this reaction (Table). Path a is generally preferred by the internal olefinic isomer of the enoi silyl ether of methyl alkyl ketones (entries 1-4, and 9) among which methyl sec-alkyl ketones (entries 1-3, and 9) overwhelmingly prefer the path a. Choice of the silyl group substantially affects path a vs. path b ratio path a becomes the favored pathway when the bulky tripropylsilyl group was used in place of the trimethylsilyl group (cf. entries 4 and 5). Thus steric hindrance at the site of the initial oxidation, the nature of the site of the proton removal (i.e., H in B), and the steric effect of the silyl group all contribute to the relative amounts of the two pathways. 

The strength of the complexes formed with ethers depends on the electronreleasing capacity and the steric configuration of the particular ether used (Table V). Initially, it was planned to deactivate TEA by reaction with a strong complex... 

Rearrangement Reactions Table 2 1,2-Wittig Rearrangement of Benzyl Ethers... 

The demand for environmentally friendly chemistry and its widespread applicability have made water an increasingly popnlar solvent for organic transformations. Mixtures of water and other solvents snch as tetrahydrofnran are now commonly anployed for a number of organic transformations. For instance, the Lewis acid catalysed aldol reaction of silyl enol ethers, commonly known as the Mnkaiyama aldol reaction, which was firstly reported in the early seventies, can be carried ont in snch media. With titanium tetrachloride as the catalyst this reaction proceeds regioselectively in high yields, but the reaction has to be carried ont strictly nnder non-aqneons conditions in order to prevent decomposition of the catalyst and hydrolysis of the sUyl enol ethCTS. In the absence of the catalyst it was observed that water had a beneficial influence on this process (Table 4, entry D) . Nevertheless, the yields in the nncatalysed version WCTe still unsatisfactory. Improved results were obtained with water-tolerant Lewis acids. The first reported example for Lewis acid catalysis in aqueous media is the hydroxymethylation of silyl enol ethers with commercial formaldehyde solution using lanthanide trillates. In the meantime, the influence of several lanthanide triflates in cross-aldol reactions of various aldehydes was examined " " ". The reactions were most effectively carried out in 1 9 mixtures of water and tetrahydrofnran with 5-10% Yb(OTf)3, which can be reused after completion of the reaction (Table 19, entry A). Although the realization of this reaction is quite simple, the choice of the solvent is crucial (Table 20). 

Hetero-Diels-Alder reactions of l-oxa-l,3-butadienes with vinyl ethers, which lead to 3,4-dihydro-2H-pyran derivatives, are synthetically equivalent to Michael type conjugate additions. Wada and coworkers presented the first examples of a catalytic asymmetric intermolecular hetero-Diels-Alder reaction by the use of ( )-2-oxo-l-phenylsulfonyl-3-alkenes 25 and vinyl ethers 26 (Table 3) [25]. 

An early example by Reetz and co-workers [79] demonstrated the evaluation of a series of biocatalysts for the hydrolytic kinetic resolution of chiral glycidyl phenyl ethers. Employing a fused-silica reactor, the authors developed an integrated reaction system capable of performing biocatalytic hydrolysis, along with separation and detection of the reaction products. Using the enantioselective hydrolysis of 2-phenoxymethyloxirane (136) to 3-phenoxypropane-l,2-diol (137) as a model reaction (Table 6.14), the authors evaluated the biocatalytic activity of a series of epoxide... 

Annulated cyclobutanones (83-86) were obtained in high yields upon reaction of ketenes with a number of heterocycles containing a vinyl ether moiety (Table II).29,30,83-85 The reported cycloadducts 83 and 84 were all formed in a stereospecific manner, in agreement with the polarization of the two -electron systems.30,83 The reactions were fast except when the reacting endocyclic carbon-carbon double bond was not substituted with an oxygen atom, such as the formation of 87 from 2,5-dihydrofuran (Table II). Furthermore, the various ketenes showed... 

---