Dicyclohexyl-24-crown-8-ether

In the presence of dicyclohexyl-18-crown-6 ether, potassium fluoride converts fluonnated vinylic iodides to acetylenes [2] (equation 2)... 

Dehydrochlorination of bis(tnfluoromethylthio)acetyl chloride with calcium oxide gives bis(trifluoromethylthio)ketene [5] (equation 6) Elimination of hydrogen chloride or hydrogen bromide by means of tetrabutylammonium or potassium fluoride from vinylic chlorides or bromides leads to acetylenes or allenes [6 (equation 7) Addition of dicyclohexyl-18-crown-6 ether raises the yields of potassium fluoride-promoted elimination of hydrogen bromide from (Z)-P-bromo-p-ni-trostyrene in acetonitrile from 0 to 53-71 % In dimethyl formamide, yields increase from 28-35% to 58-68%... 

Formation constants K for complexes of dicyclohexyl-18-crown-6 ether with various cations. Note that, although the radii of Ca ", Na" and Hg + are very similar, the ratio of the formation constants is 1 6.3 225. Again, K" and Ba " have similar radii but the ratio of K is 1 35 in the reverse direction (note log scale). 

Y,7-Dimethylallyl bromide and geranyl bromide are converted into the corresponding aldehydes in 75 and 82% yields, respectively, by heating at 100 °C with sodium dichromate in hexamethylphosphoramide in the presence of dicyclohexyl-18-crown-6 ether [614]. Similar results are achieved with polymer-supported chromic acid [540] (equation 192). 

The classical permanganate oxidation of a-pinene yields cis-pinonic acid (383). Now, using dicyclohexyl-18-crown-6 ether in benzene, the yield has been raised to 90%. In the conventional oxidation, the yield of the acid (383) is very low, but in the neutral part the interesting ether (384) has been found. This is quantitatively dehydrated by thionyl chloride to (385), which has led to the synthesis of ( - )-7-epichrysanlhenol (386), the structure of which was linked to chrysanthe-none by oxidation. It has been noted that with iodosobenzene diacetate and... 

Add solid potassium carbonate and dicyclohexyl-18-crown-6 ether to polymer in THF and reflux. 

Phase transfer catalyzed reactions in which ylides are formed from allylic and ben-zylic phosphonium ions on cross-linked polystyrenes in heterogeneous mixtures, such as aqueous NaOH and dichloromethane or solid potassium carbonate and THF, are particularly easy to perform. Ketones fail to react under phase transfer catalysis conditions. A phase transfer catalyst is not needed with soluble phosphonium ion polymers. The cations of the successful catalysts, cetyltrimethylammonium bromide and tetra-n-butylammonium iodide, are excluded from the cross-linked phosphonium ion polymers by electrostatic repulsion. Their catalytic action must involve transfer of hydroxide ion to the polymer surface rather than transport of the anionic base into the polymer. Dicyclohexyl-18-crown-6 ether was used as the catalyst for ylide formation with solid potassium carbonate in refluxing THF. Potassium carbonate is insoluble in THF. Earlier work on other solid-solid-liquid phase transfer catalyzed reactions indicated that a trace of water in the THF is necessary (40). so the active base for ylide formation is likely hydrated, even though no water is included deliberately in the reaction mixture. 

Both 5n1 and 5n2 rate constants for (he formation of ester between benzyl bromide and potassium 4-nitrobenzoate using dicyclohexyl-18-crown-6-ether as a phase transfer agent have been determined. ... 

The Importance of this particular chelation is supported by the observations that -methoxy and -methyl groups increase the yield of crystalline isotactic polymer, while -chloro or 2,6-dimethyl groups decrease the isotactic fraction (14). The general importance of the chelation in establishing stereochemistry is supported by the observations that addition of dicyclohexyl 18-crown-6 ether in an amount equivalent to catalyst, or of solvents coordinating strongly with K., such as dimethyl-sulfoxide or hexamethylphosphortriamide (HMPT), markedly decrease the crystalline polymer from either t-butylethylene oxide or phenyl glycidyl ether (14),... 

Perfluoro cis-syn-cis- and cis-anti-cis-Dicyclohexyl[18]Crown-6 Ether. Very recently we have synthesized perfluoro crown ethers from the hydrocarbon dibenzo crown ether (see Figure 8) (10). We have prepared two interesting isomers of perfluorodicyclohexyl[18]crown-6 ethers fi0),the cis-syn-cis and cis-anti-cis isomers. Their structures have also been established by X-ray crystallography. 

Figure 4. Single crystal X-ray structure of perfluoro -cis-syn-cis-dicyclohexyl[18]crown-6 ether.

Figure 5. Unit cell packing of perfluoro-cis-syn-cis-dicyclohexyl-[18]crown-6 ether.

Figure 15. The superposition of the carbon and oxygen atoms of the perfluoro -cis-syn-cis-dicyclohexyl[18]crown-6 ether (solid lines) onto the equivalent atoms of perfluoro [18]crown-6 ether (dashed lines) illustrating the similar configuration of the perfluoro ether rings of the two structures.

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