Ether formation displacement

Fenticonazole (106), on the other hand, is used topically to combat a wide variety of dermatophytes and yeasts, particularly Candida albicans. It can be synthesized from 2,4-dichlo-rophenacyl chloride (104) by reduction with borohydride and subsequent displacement with imidazole to give 105. This last undergoes ether formation with p-thiolphenylbenzyl chloride mediated by NaH to produce fcnticonazole (106) [37]. 

Thioamide formation benzodiazepinone, 505 heteiodiazepinone, 621 phosphorus pentasulf ide, 323, 600 Thioazole formation, nitrile addition, 301 Thiocarbamate formation, 588 phenol, 95 rearrangement, 517 Thioenol ether formation, 185, 517 addition-elimination, 554 Thioester formation, mixed anhydride, 184 Thioether formation, 241, 300, 413, 416 alkylation, 586, 588 aromatic displacement, 416 Thiohydantoin formation, 293 Thiol interchange, benzothiazole formation, 422... 

At lower temperatures the oxonium salt or the alkyl hydrogen sulfate may react by an SN displacement mechanism with excess alcohol in the reaction mixture, thereby forming a dialkyl ether. Although each step in the reaction is reversible, ether formation can be enhanced by distilling away the ether as fast as it forms. Diethyl ether is made commercially by this process ... 

It should be kept in mind that Lewis acids reactions with DHA also led to the formation of dimers and/or of anhydroartemisinin (AHA) 23, often as a major product. To circumvent this problem, DHA was converted to the C12 acetate, which was displaced by ether formation. 

Parera and his co-workers (359-362) have studied the poisoning effect of amines, pyridine, phenol, and acetic acid. A reduced rate of ether formation from methanol at the standard temperature of 230°C was observed when the poisons were present in the feed. In most cases the original activity was recovered, although rather slowly. Most probably the poisons were either displaced by alcohol and/or water or removed from the surface by chemical transformations. 

Hammett p values have been established for the displacement reaction leading to ether formation. In the case of ether formation from ROH and R CH2X, the p value was negative for substituent changes in R, and positive for changes in R [26]. 

The chemistry presented in the previous two sections focussed on the formation of hydroxyolefins followed by cyclization to the desired C-glycosides. The latter steps in the examples shown rely largely upon the cyclization of protected polyols. In this section, cyclization methods including ether formations, ketal formations and halide displacements are presented. 

Although technically ether formations, the displacement of halides by hydroxyl groups differs from the examples presented above in that these reactions are base mediated. As such, under these conditions, C-glycosidations complement the previously described cyclization strategies given that they allow reactions with acid sensitive substrates. As shown in Scheme 7.100, Schmid and Whitesides [244] used this approach in the preparation of C-furanosides. Specifically, the illustrated... 

An interesting process that may take place during cellulose pyrolysis is the inter-chain ether formation. This process is very unlikely for hydroxyl groups at C-2, C-3 or C-4 of the glucose units by water elimination between two chains. However, from energy considerations a displacement process involving one of the acetal oxygens seems possible ... 

Fig. 22. A binary mixture of 2/3DN30C10 and DAP(Bn)22+ behaves in a manner analogous to an XNOR gate. In the absence of acid or base, a strong complex with pseudorotaxane geometry is formed, a Upon addition of trifluoroacetic acid (A), by virtue of the formation of a strong complex with the crown ether, protons displace the DAP(Bn)22+ from the cavity of 2/3DN30C10. b Neutralization of the solution with n-butylamine (B) results in the reformation of the pseudorotaxane. c If the initial mixture is treated with base, a strong interaction between n-butylamine and DAP(Bn)22+ leads to the destruction of the complex, d Neutralization of the solution with TFA leads to a simple acid-base reaction, and pseudorotaxane formation. If the two inputs are acid and base (A and B), with a 1 signaling presence and a 0 absence, this system behaves as an XNOR gate, if pseudorotaxane formation is represented by an output of 1...

If the electrophile is a vinyl triflate, it is essential to add LiCl to the reaction so that the chloride may displace triflate from the palladium o-complex. Transmetallation takes place with chloride on palladium but not with triflate. This famous example illustrates the similar regioselectivity of enol triflate formation from ketones to that of silyl enol ether formation discussed in chapter 3. Kinetic conditions give the less 198 and thermodynamic conditions the more highly substituted 195 triflate. 

Formation of oxacycles via intramolecular radical addition reactions of oxygen-centered radicals under oxidative and reductive conditions is known [116] (see also Chapter 5.2, Volume 2). However, cyclic ether formation via intramolecular displacement reaction of iodohydrins obtained by hydrogen abstraction of oxy radicals has been more widely used, as exemplified in the reports by Suarez [117]. The usefulness of this reaction was amply demonstrated by Paquette in the synthesis of (-t-)-epoxydiclymene (179) [118] (Scheme 61), in which the strained trans-... 

Other Alkyl and Aryl Ethers - A number of 3-0-aminoalkyl-l,2-0-isopro-pylidene-a-D-gluco-or xylo-furanoses have been synthesized and evaluated for antiviral activity. Some 6-0-alkyl-a-D-glycopyranosides have been prepared by displacement of 6-0-tosylates with alkoxides, while the regioselectivity of 3- or 5-0-ether formation on l,2-0-isopropylidene-4,6-di-0-benzyl-/n> o-inositol has been shown to depend on the nature of the 0-alkylating agent. A facile synthesis of methyl 2-or 3-0-allyl-5-0-benzyl-p-D-ribofuranoside has been described. ... 

Condensation of 2,6-bis(hydroxymethyl-4-methylphenol) under neutral conditions leads to polymers with exclusively benzylic ether linkages and with molecular weights between 2,500 and 20,000. Dibenzyl ether formation is probably a catalyzed 8 2 reaction, involving the displacement of a hydroxyl group. These resins do not show hyperacidity, but they have remarkable affinity towards divalent metal ions. 

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