Isomerization hydro

In this series of amides, hydrolysis or aminolysis of a simple ester, cleavage of a silyl groups a cis/trans isomerization, or reduction of a quinone to a hydro-quinone exposes an alcohol that then induces deprotection by intramolecular addition to the amide carbonyl. 

Likewise, the isomeric fused aziridines 22 and 24, obtained from 1,4,5,6,7,8-hexahydronaph-thalene, undergo bromination. dehydrobromination and ring expansion to the 6,7,8,9-tetra-hydro-3//-3-benzazepine 23 and the 2,7-bridged azepine 25, respectively.61... 

Kinetics studies have demonstrated that the isomerization is a first-order process, characterized by the activation parameters AH% = 34.5(8) kcal mol-1 and A St = 6(2) e.u. Such rearrangements of poly-(pyrazolyl)borato ligands are not uncommon, and have also been observed for Cu and Co complexes of the tris(3-isopropylpyrazolyl)hydro-borato ligand system, i.e., [T73-HB(3-Pr pz)3]M — [T73-HB(3-Pr1pz)2(5-Pr pz)]M (32). 

We developed a convenient synthesis of 3-cyclopentenyl hydroperoxide via hydro-boration and autoxidation of cyclopentadiene, and bromination proceeded smoothly to afford 32 40). Ring closure with silver trifluoroacetate (Eq. 26) afforded a 5-bromo-2,3-dioxabicyclo[2.2.1]heptane 34 (6%) and a 5-trifluoroacetoxy-2,3-dioxabicyclo-[2.2.1]heptane 35 (14%), and it was shown independently that 34 is rapidly converted into 35 by reaction with Ag02CCF3. To avoid the trifluoroacetate bromide substitution that accompanies and competes with the dioxabicyclization, 32 was treated with silver oxide and this slowly yielded an isomeric 5-bromo-peroxide 33 (42 %) (Eq. 26). 

Alkene isomerization has both positive and negative aspects. The positive aspect is where isomerization is needed prior to, for example, hydro formylation to give the desired product. The negative aspect of alkene isomerization is similar to that described in Section 2.6.2.1 on hydrogenation. The byproduct must be separated from both catalyst and product, and recycle opportunities may be limited. Not only is isomerization a direct efficiency loss, but when the isomerised alkene is purged, desired reactants will likely also be lost. 

Denmark pursued intramolecular alkyne hydrosilylation in the context of generating stereodefined vinylsilanes for cross-coupling chemistry (Scheme 21). Cyclic siloxanes from platinum-catalyzed hydrosilylation were used in a coupling reaction, affording good yields with a variety of aryl iodides.84 The three steps are mutually compatible and can be carried out as a one-pot hydro-arylation of propargylic alcohols. The isomeric trans-exo-dig addition was also achieved. Despite the fact that many catalysts for terminal alkyne hydrosilylation react poorly with internal alkynes, the group found that ruthenium(n) chloride arene complexes—which provide complete selectivity for trans-... 

Catalytic processes (finid catalytic cracking, catalytic hydrocracking, hydro-treating, isomerization, ether manufacture) also create some residuals in the form of spent catalysts and catalyst fines or particulates. The latter are sometimes separated from exiting gases by electrostatic precipitators or filters. These are collected and disposed of in landfills or may be recovered by off-site facilities. The potential for waste generation and hence leakage of emissions is discussed below for individual processes. 

This reaction also proceeds in the presence of hydrogen only thus, it may never predominate since under these conditions more rapid hydrogenation of the double bond competes very efficiently with it. Due to rapid double bond isomerization the product contains predominantly the most stable isomer 1-methylcyclopentene. The dependence of the selectivity of hydro-genative versus dehydrogenative cyclization on the structure of the starting hydrocarbon (Fig. 7) shows that methylcyclopentene (MCPe) is not the product of secondary dehydrogenation (55). 

Two 4-methylene-l,3-dioxane diastereoisomers, isomeric at C-6, were subjected to the rhodium-catalyzed hydro-formylation. The stereochemistry of the newly formed stereogenic carbon was guided solely by the acetal stereocenter (not by C-6) (Scheme 56) <1997JA11118, 1998TL6423>. 

The preparation of acyclic allylic hydroperoxides has been described before (3, 7, 9), but it is not clear how the reactivities differ from the better known saturated hydroperoxides and cyclic allylic hydroperoxides. Dykstra and Mosher prepared allyl hydroperoxide by the reaction of allyl methanesulfonate with hydrogen peroxide and alcpholic potassium hydroxide and purified the hydroperoxide by gas chromatography. It detonated on heating and decomposed on exposure to light but was relatively stable in the cold and dark. The isomeric allylic hydroperoxides formed from the autoxidation of the branched olefin, 4-methyl-2-pentene, have also been isolated and were not abnormally reactive (3). In the present study, cis- and trans-2-butene were photooxidized in the presence of methylene blue as a sensitizer (14), and the product, l-butene-3-hydro-peroxide, was isolated by preparative chromatography. 1-Butene proved unreactive and 2-butene-l-hydroperoxide could be formed only by isomerization of the secondary hydroperoxide. 

Synthesisfrom 7-Hydroxygeranylj-neryl Dialkylamine. The starting material can be obtained by treatment of myreene with a dialkylamine in the presence of an alkali dialkylamide, followed by hydration with sulfuric acid. The 7-hydroxygeranyl/-neryl dialkylamine isomerizes to the corresponding 7-hydro-xyaldehyde enamine in the presence of a palladium(II) phosphine complex as catalyst. Hydrolysis of the enamine gives 7-hydroxydihydrocitronellal [70]. 

For the conversion of l,6 2,3-dianhydro-4-deoxy- and l,6 3,4-dian-hydro-2-deoxy-/3-DL-(i/ ro-hexopyranoses (261 and 262) lithium diethylamide was successfully employed.151 However, attempts at isomerization of methyl 2,3-anhydro-4-deoxy- or -4,6-dideoxy-DL-hex-opyranosides (263 R1 = CH2OH, CH3, R2 = Me) with butyllithium failed, because of predominance of secondary reactions (for example, opening of the oxirane ring with BuLi).14(i The yields of desired products were negligible or nil. 

Disjoint functionalities also exist in chloral and this property has been exploited in the isomerization of 4-hydro xy-2-cyclopentenones [206]. 

Condensation of 7-methoxy-3,4-dihydro-1(2H)-naphthal-enone with tetramethylene dibromide by means of NaH in benzene or tert amyl alcohol gives 3,4-dihydro-7-methoxy-2,2-tetramethylene-1(2H)-naphthalene (bp (0,05 mbar) 120-123 °C), which is treated with acetonitrile and butyllithium in THF yielding 1-hydroxy-7-methoxy-1,2,3,4-tetrahydro-2,2-tetramethylene-1-naphthalene-acetonitrile (mp 140-142 °C). This compound is reduced with LiAIH4 in THF to afford hydro-2,2-tetramethylene-1-naphthol (mp 178-180 °C), and isomerized to 4a-(2-aminoethyl)-1,2,3,4,4a,9-hexahydro-6-methoxy-phenantrene i (mp 187 °C). 

Hydrocarboxymethylation of Long-Chain Alkenes. An industrial process to carry out hydrocarboxymethylation of olefins to produce methyl esters particularly in the Ci2-Ci4 range for use as a surfactant feedstock was developed by Huels.183 A promoted cobalt catalyst in the form of fatty acid salts (preferably those formed in the reaction) is used. With high promoter catalyst ratio (5 1-15 1) at 180-190°C and pressure of 150-200 atm, the rate of alkene isomerization (double-bond migration) exceeds the rate of hydrocarboxymethylation. As a result, even internal olefins give linear products (the yield of normal products is about 75% at 50-80 % conversion). Secondary transformations of aldehydes (product of olefin hydro-formylation) lead to byproducts (ethers and esters) in small amounts. 

It is pointed out that although aqueous sulphurous acid appears to contain most of its sulphur dioxide as such,1 yet solutions of the alkali bisulphites appear to contain some pyrosulphite (metabisulphite).2 It is therefore not unreasonable to assume that some free pyrosulphurous acid is present in aqueous sulphurous acid solutions. Since hydro-sulphurous acid is unstable under the prevailing conditions, it does not accumulate, but rapidly undergoes further change, which makes proof of its formation difficult. It is assumed 3 that some of the colourless acid formed in reaction (1) undergoes rearrangement to the isomeric coloured form ... 

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