Pyridine ethers

Acetyl-5-deoxy-l,2-0-isopropylidene-[3-iJ - threo - pent - 4 - enofura-nose (34). (1) From 3-0-acetyl-5-deoxy-5-iodo-1,2-0-isopropylidene- -d-xylofuranose (31). Anhydrous silver fluoride (7.5 grams) was added to a solution of 7.2 grams 26 in dry pyridine (50 ml.), and the mixture shaken at room temperature for 24 hours. The black reaction mixture was diluted with ether (50 ml.), and the supernatant liquid was decanted from the dark, inorganic residue. The residue was further extracted with ether (3 X 50 ml.) and the pyridine-ether solution partially decolorized... 

We have shown that pyridine forms stable complexes with Zr(benzyl)4, and that ethers may also coordinate in a similar way. Pyridine, ethers, and olefins may be considered as a class of Lewis bases, the strength of which is determined by the position of the equilibrium ... 

The filtrate, which results from the separation of product 1, is evaparated to dryness in vacuum. The residue, which mainly contains unreacted digoxin, is purified by recrystallization from pyridine/ether/water (3.5 5 40) and repeatedly acetylated. It can then be recycled to produce more p-acetyldigoxin. The filtrate resulting from the separation of product 2 is evaporated to dryness. The resulting residue contains the di- and polyacetyl derivatives of digoxin, which are deacetylated to digoxin in a known manner... 

In the preparation of the adduct of B(CH3)3 with ether, pyridine (C5H5N) cannot be used as a solvent. In the preparation of the adduct of B(CH3)3 with pyridine, ether can be used as the solvent. Explain the difference between the two cases. 

Reaction with P-Donors. In accord with the expectations dis-cussed above, Cp2Mo2(C0K reacts readily with two equivalents of soft nucleophiles, e.g., phosphines, phosphites, CO, etc., to give exclusively the trans-products indicated in eq. 7. With one equivalent of ligand, only disubstituted product (1/2 equiv.) and unreacted 1 (1/2 equiv.) are isolated. Hence, the addition of the first ligand is the slow step (eq. 18). Complex 1 does not react with hard bases, e.g., aliphatic amines, pyridine, ethers, alcohols, or ketones. Bulky phosphines, e.g., (cyclohexyl)3P, and Ph3As or Ph3Sb also fail to react at room temperature. Rather... 

Related to this is the tendency for many workers to choose complicated systems for study. Solvents with known associating tendencies and sometimes even mixtures of these are used. Imagine the conflicting interactions in a system made up of a fatty acid dissolved in a pyridine-ether mixture. 

Thallium diphenyl pyrophosphate crystallises from pyridine-ether solution in short, microscopic needles which are completely soluble in pyridine, moderately soluble in boiling glacial acetic acid, less soluble in alcohol, ethyl acetate, or chloroform, and insoluble in acetone, ether, carbon tetrachloride, or light petroleum. 

Intramolecular participation of a neighboring hydroxy group is observed in the rearrangement of erythromycin A oxime (24) with p-toluenesulfonyl chloride and sodium hydrogencarbonate in acetone-water (equation 12). Interestingly, with the same reagent in pyridine-ether only the normal rearrangement product (25) is formed. 

Another well-known process that utilizes a nucleophilic phosphane is the Mit-sunobu reaction, that is, the reaction between an acidic partner and an alcohol, typically facilitated by an azodicarboxylate and a phosphane. Two options are possible, anchoring of the electrophilic part to the solid support, dealt with in the next section, or anchoring of the nucleophilic phosphane. Georg et al. used polystyrene-bound triphenylphosphane and DEAD (diethyl azodicarboxylate) in their synthesis of aryl ethers [31]. Alcohols were reacted successfully with electron-rich and electron-deficient phenols, giving the desired products in good yield and purity. More recently, Wilhite and coworkers disclosed an efficient protocol for the synthesis of pyridine ethers using ADDP [l,l -(azodicarbonyl)dipiperidine] and polymer-supported triphenylphosphane (Scheme 6.9) [32], Both methods eliminate purification problems caused by triphenylphosphane oxide, but chromatography is still needed. 

Orange-red crystals from benzene + methanol, mp 178-180. Absorption max (chloroform) 472-478 ntn. Freely sol in carbon disulfide, chloroform, benzene. Slightly sol in pyridine, ether. Practically insol in methanol. Provitamin A activity 54% of that of aII-trans-0 -carotene. 

Treatment of (S)-Af-methylbenzenesulfinamide (16) with chlorine in pyridine-ether gave... 

Figure 9-20 A homoconjugated macrocycle with alternating alkyne and diyne units (a) EtMgBr, then CuCI, then 8 (b) KOH, MeOH, 56% for 47 - 69 (c) CufOAcjj, 6 1 pyridine/ether, 14%.

The black-purple tetramethyloctadehydrotridecapentadecafulvalene 654 was obtained in 22% yield by the oxidative ring-closure of 653 mediated by copper(II) acetate in pyridine - ether - methanoP. ... 

Dimethyl sulfate alkylates almost quantitatively sterically hindered aromatic poly(pyridine ether)s and poly(pyridine ether sulfone)s in nitrobenzene. The reaction can be illustrated as follows ... 

The pH concept is most commonly used for dilute aqueous media however, a similar formalism can be extended to other systems. The extent of the pH scale, which in aqueous media can be described as 14 units, depends on the autoprotolysis constant of the amphiprotic solvent, so that the equivalent range, e.g., in methanol, equals 16.7 units, in sulfuric acid 2.9 units, and in acetic acid 14.5 units. In such solvents, as in water, the pH of neutrality corresponds to the middle of this range. Such reasoning cannot be extended to protophilic (e.g., pyridine, ethers), and aprotic (e.g., hydrocarbons) solvents, for which the logan+ scale is from one or both sides, respectively, unlimited. 

The activating influence of the ring nitrogen provides an important versatility for the synthesis of pyridones, pyridinols, and pyridine ethers, by nucleophilic substitution at the 2- and 4- and even the 3-position. Further, the potential of accomplishing these substitutions via pyridine W-oxides contributes to the scope of this method. 

Solutions of I2 in donor solvents, such as pyridine, ethers or ketones, are brown or yellow. Even benzene acts as a donor, forming charge transfer complexes with I2 and Br2. The colours of these solutions are noticeably different from those of I2 or Br2 in cyclohexane (a non-donor). Whereas amines, ketones and similar compounds donate electron density through a a lone pair, benzene uses its vr-electrons. This is apparent in the relative orientations of the donor (benzene) and acceptor (Br2) molecules in Fig. 17.6b. The fact that solutions of the charge transfer complexes are... 

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