Dienes epoxidation

Monomers which can be polymerized with aromatic radical anions include styrenes, dienes, epoxides, and cyclosiloxanes. Aromatic radical anions... 

Often, considerable selectivity is encountered, as for instance in the case of the 5,9-diene epoxide (7), which affords the 6j8-fluoro-5a-bromide (8), with... 

Studies conducted by Barenghi eta.1. (1990) and Lodge etal. (1993) independently have demonstrated the facile, multicomponent analysis of a wide range of PUFA-derived peroxidation products (e.g. conjugated dienes, epoxides and oxysterols) in samples of oxidized LDL by high-field H-NMR spectroscopy. Figure 1.9 shows the applications of this technique to the detection of cholesterol oxidation products (7-ketocholesterol and the 5a, 6a and 5/3,60-epoxides) in isolated samples of plasma LDL pretreated with added coppcr(Il) or an admixture of this metal ion with H2O2, an experiment conducted in the authors laboratories. 

Idia aemula Hilbner C2] diene epoxides Wong et al., 1985... 

Millar, J.G., Giblin, M., Barton, D. and Underhill, E. W. (1991a). Chiral lepidopteran sex attractants blends of optically active C20 and C21 diene epoxides as sex attractants for geometrid and noctuid moths (Lepidoptera). Environ. Entomol., 20,450-457. 

Isomerization of 1,3-diene epoxides. Noyori etalf have reported three types of isomerization of allylic oxides in the presence of a catalytic amount of this palladium(O) complex. One class, exemplified by the isomerization formulated in equation (I), involves transfer of a hydrogen atom from the Ca-alkyl group and results in a dienol of the type obtained in the ene reaction of singlet oxygen with 1,3-dienes. 

In principle, any functionality capable of producing a carbenium ion under strongly acidic conditions will be able to participate in a Ritter-type reaction. Such classes of compounds include alcohols, aldehydes, alkanes, alkenes, alkyl halides, carboxylic acids, dienes, epoxides, esters, ethers, glycols, ketones, IV-methylolamides and oximes. Consequently, an enormous number of examples is reported and only a representative selection can be presented here. A comprehensive listing of examples reported up to 1966 is provided in the review by Krimen and Cota. ... 

Epoxidation of 1,3-dienes with NaOCI catalyzed by S,S-2 provides only mono-epoxides with only moderate enantioselcctivity ( 45% ee). In the case of (Z,E)-dienes, epoxidation occurs with high selectivity (10 1) at the (Z)-alkenc (equation I). In contrast, high enantioselectivity can be obtained with ct. s-enynes (equation II). 

Monomers that can be polymerized with aromatic radical anions include styrenes, dienes, epoxides, thiiranes, and cyclosiloxanes. For epoxides and cyclosiloxanes, the mechanism of initiation involves nucleophilic addition of the radical anion to these monomers as shown in Scheme 7.6, in contrast to the electron transfer mechanism occurring for hydrocarbon monomers (Scheme 7.5) [45]. 

Sharifi, M. and J. Einhorn, Isomeric Differentiation of Conjugated Diene Epoxides by Polar... 

Three types (A-C) of rearrangement of 1,3-diene epoxides are realized by a catalytic amount of tetrakis(triphenylphosphine)palladium(0) in dichloromethane, benzene, or ethereal solvents (Scheme 1). The course of the Pd(0)-catalyzed reaction of the epoxides appeared to be highly dependent on the substitution pattern of the substrates. 

The diene epoxides having a transferable hydrogen atom in the C-2 alkyl substituent undergo type A reaction by hydrogen migration reaction. Some examples are shown in Scheme 2. 

Monoepoxides derived from simple cyclic 1,3-dienes possessing ordinary ring size (five- to eight-membered ring) give the corresponding /3,y-unsaturated ketones as the sole product as shown in Scheme 4. The reaction of a 12-membered ring epoxide produces a mixture of 3-cyclododecenone and the dienol. The latter is possibly formed from the type B reaction. The Pd(0)-catalyzed reaction of terminal 1,3-diene epoxides affords a,/3-unsaturated aldehydes predominantly (Scheme... 

The efQciency of these catalytic reactions of epoxides is ascribed to the eminent nucleophilic character of the Pd(0) catalyst and hydrogen-carrying ability of Pd(II) species. " In principle, the diene epoxide is susceptible to Pd(0) attack at C-2 (SN2-type reaction), C-4 (SN2 -type reaction), or C-3-C-4 double bond. /3,y-Unsaturated ketone would form via zwitterion and Pd hydride intermediate, while, alternatively, the epoxide can isomer-ize to dienols through the 7r-allyl complex (Scheme 7). The Tt-allyl complex is facilely scavenged with hydride, alkoxides, amides, and carboanion nucleophiles to enhance the synthetic utility (see Sect. V.2.1.5). 

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