Ethers cyclic, cleavage

Ether cleavage. Cyclic ethers, particularly tetrahydrofuranes, are cleaved by magnesium bromide and acetic anhydride in acetonitrile to oj-bromoacetates. The reaction occurs with inversion (8 2). 

The reductive cleavage of -bromo ethers is a related reaction. If the ether is cyclic, the reverse reaction takes place on treatment with NBS ... 

Ether cleavage and further functionalization afforded the intermediate 268. The [5+2]-cycloaddition provided the hydroazulene 267 with the correct relative configuration at and C. Tracing back the synthesis of the pyryli-um ylide 266 leads to the astonishing realization that 2-methyl cyclopent-2-enone (90) was the original cyclic starting material and that the methyl as well as the isopropyl group were introduced by a sequence of cuprate addition and enolate alkylation (see Schemes 15, 31 and 36 for comparison). 

Hydrolysis of cyclic orthoesters Ozonolysis of tetrahydropyranyl ethers Cleavage of vinyl orthoesters... 

The reaction that takes place is hydrogen halide-promoted ether cleavage. In such a reaction with excess hydrogen halide, the C—O—C unit is cleaved and two carbon-halogen bonds are formed. This suggests that cineole is a cyclic ether because the product contains both newly formed carbon-halogen bonds. A reasonable structure consistent with these facts is... 

Epoxides, summary of chemistry, 290 Equatorial bond, 168 Equilibrium and free energy, 36 Equivalent H s, 50 Erythro form, 82, 85 Esters, formation, 338 inorganic, 262, 272, 276 reduction, 261 Ethers, cleavage, 282 crown, 286 cyclic, 285 silyl, 286... 

The R3AI can be substituted by R Li or R MgX, although the yields are lower (borate formation, ether cleavage). Moderate yields of cyclic triorganoboranes R2BR are obtained from the reaction between R BX2 (X = F, Cl) and dimetallated hydrocarbons (M = Li, MgX) ... 

Deprotection. Cleavage of benzyl ethers and cyclic acetals by heating with large amounts of this catalyst [20% Pd(OH)2/C] in MeOH is totally impractical. It does not seem to offer any advantage over the less expensive Pd/C. 

However, unlike the triaryIsulfonium salts, these compounds undergo reversible photoinduced ylid formation rather than homolytic carbon-sulfur bond cleavage. Because the rate of the thermal back reaction is appreciable at room temperature, only those monomers that are more nucleophilic than the ylid will polymerize. Epoxides, vinyl ethers, and cyclic acetals undergo facile cationic polymerization when irradiated in the presence of dialkylphenacylsulfonium salts as photoinitiators. 

Organic Reactions contains a review of the fission of benzyl ethers, including cyclic benzyl ethers, by hydrogenation.43 Ring fission of furans has been reviewed by Jones and Taylor.44 Burwell45 has written an excellent and detailed report on the cleavage of ethers, in which he discusses also the theoretical problems involved he concludes with some indications for the fission of sulfides, a subject that is treated also by Tarbell and Hamish.46... 

Enone synthesis. The Smii-cait aldehydes (Reformatsky-type reaction Cyclic ether cleavage. Smli is a with acid chlorides. It also contributes ai Boronate esters. Hydroboration < by Smlj. 

Cyclic ether cleavage. Sml. is a typical Lewis acid, which induces reaction with acid chlorides. It also contributes an iodide ion, giving ni-iodoalkyl carboxylates. 

Allylic substitutions. The catalyt preparation of (V-protected allylic amio cyclic carbamates. Asymmetric a-allj ried out by treating the enamines d (Ph3P)4Pd and subsequent hydrolysis. 1 bonates to l-allyl-2(l//)-pyrimidinonei peptides through ester enolate Claisci set. l-Arylprop-2-enols are suitable fa allyl ether cleavage treatment with a < suffices. 

Mild and rapid ether cleavage Halogenhydrins from cyclic ethers... 

Without additional reagents Cyclic ethers via cyclic carbonic acid esters Transesterification s. 72, 350 Thermal cleavage of dicyclopentadienes... 

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