Epoxides conversion into allylic alcohols

Since the starting tellurides are easily prepared (see Section 3.1.3.2) from the corresponding alkyl bromides and tellurolate ions, and -hydroxyalkyl tellurides by the opening of epoxides with the same reagents, the combined procedures furnish a method for the dehydrobromination of alkyl bromides and for the conversion of epoxides into allylic alcohols. Moreover, combining the telluroxide elimination with the methoxytelluration of olefins (see Sections 3.9.3.2 and 4.4.8.3), allylic and vinylic ethers are easily prepared. 

Lygo, B. and To, D.C.M., Asymmetric Epoxidation via Phase-transfer Catalysis Direct Conversion of Allylic Alcohols into a, -Epoxyketones. Chem. Commun. 2002, 2360-2361. 

Selenides and selenolate anions are usually less basic and more nucleophilic than corresponding sulfur compounds. This unique property was recognized in 1973 by Sharpless and Lauer and used for the conversion of epoxides into allylic alcohols [18]. This publication can be regarded as another milestone in organoselenium chemistry. New aspects and a variety of other related reactions are summarized by M. Iwaoka and S. Tomoda in Chap. 3. 

Another synthetic application of selenoxides is the conversion of epoxides into allylic alcohols (equation 594) [168. Dehydrogenation occurs almost exclusively away from the hydroxyl group. 

Electrochemical oxidations have been previously mentioned.122 A novel application is the regioselective epoxidation (80% conversion 90% selectivity) at the 6,7-bond of geranyl and neryl esters and phenyl sulphones.214 Another is the one-step conversion of olefins into allylic alcohols via electrooxidative-oxyselenylation-deselenylation, e.g. (97)—>(99). This method has been applied to the synthesis of (100) which can be converted (70%) into marmelolactone [(101) from quince], and... 

For conversion of epoxides 280 into 3,4-unsaturated pyranosides 281, Brown employed the well-known isomerization of oxiranes into allylic alcohols, which is induced by strong bases, for example, -butyl lithium. It was found that for the isomerization of 351 and 352 to the corresponding allylic alcohols 353 and 354, lithium diethyl amide was more effective with n-butyl lithium other reactions took place. 

Allylic Alcohols. Full details have appeared of the conversion of epoxides into allylic alcohols, mediated by trimethylsilyl trifluoromethanesulphonate (Scheme 4) (see 6,163 4,145), and this sequence is mentioned in a review of trialkylsilyl perfluoroalkanesulphonates as reagents opening of an epoxide ring occurs at the more substituted centre. The use of trimethylsilyl iodide for the epoxide-allyl alcohol transformation (5, 158) is discussed in a review of the preparation and applications of this reagent. ... 

As a further application of the reaction, the conversion of an endocyclic double bond to an c.xo-methylene is possible[382]. The epoxidation of an cWo-alkene followed by diethylaluminum amide-mediated isomerization affords the allylic alcohol 583 with an exo double bond[383]. The hydroxy group is eliminated selectively by Pd-catalyzed hydrogenolysis after converting it into allylic formate, yielding the c.ro-methylene compound 584. The conversion of carvone (585) into l,3-disiloxy-4-methylenecyclohexane (586) is an example[382]. 

The combination of the preceding method of obtaining allyl alcohols with the Sharpless kinetic resolution (SKR) of secondary allyl alcohols allows conversion of the original racemic allyl alcohol into a pure enantiomer with a 100% theoretical yield. By this procedure, the glycidol obtained by the SKR epoxidation of the secondary allyl alcohol is converted into the corresponding mesylate and then treated with the Te ion, furnishing the allylic alcohol with the same configuration of the enantiomer in the SKR which... 

Most attention has been devoted to the conversion of epoxides derived from 2-alkoxy-5,6-dihydro-2ff-pvrans into unsaturated allylic alcohols, that is, alkyl 3,4-dideoxy-DL-ald-3-enopvranosides (256). Ad-... 

The epoxy-Ramberg-Backlund reaction (ERBR) has been used for the conversion of a,/3-epoxy sulfones into a range of mono-, di-, and tri-substituted allylic alcohols.34 Modification of this method has permitted the preparation of enantio-enriched allylic alcohols following the diastereoselective epoxidation of enantio-enriched vinyl sulfones that were accessed efficiently from the chiral pool. 

Fig. 3.40. Sharpless epoxida-tions of chiral racemic secondary allylic alcohols (in contrast to the upper half of Figure 3.39) driven to a 100% conversion divided into 50% rapid and also highly diastere-oselective epoxidation of the matched pair, and 50% slow epoxidation in the mismatched pair where hardly any diastere-ocontrol occurs.

The efficiency of kinetic resolution is even greater when there is a silicon or iodo substituent in the (3 )-position of the C-1 chiral allylic alcohols. The compatibility of silyl substituents with asymmetric epoxidation conditions was first shown by the conversion of (3 )-3-trimethylsilylallyl alcohol into (2/ ,3/ )-3-trimethylsilyloxiranemethanol in 60% yield with >95% and further exploited by the conversion of ( )-3-(triphenylsilyl)-2-[2,3- H2]propenol into (2 ,3/ )-3-triphenylsilyl[2,3- H2]oxirane-methanol in 96% yield and with 94% gg.io7b,i07c. pentyl group at C-1, the k,A for asymmetric... 

During the conversion of alkenes into epoxy alcohols by allylic oxidation with singlet oxygen, an oxygen atom is usually removed from the allylic hydroperoxide by reduction, only to be subsequently reintroduced in the resulting epoxy alcohol by epoxidation with an external oxygen donor. 

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