Epoxidation of dienes

Vinyl epoxides are highly useful synthetic intermediates. The epoxidation of dienes using Mn-salen type catalysts typically occurs at the civ-olefin. Epoxidations of dienes with sugar-derived dioxiranes have previously been reported to react at the trans-olefin of a diene. A new oxazolidinone-sugar dioxirane, 9, has been shown to epoxidize the civ-olefin of a diene <06AG(I)4475>. A variety of substitution on the diene is tolerated in the epoxidation, including aryl, alkyl and even an additional olefin. All of these substitutions provided moderate yields of the mono-epoxide with good enantioselectivity. 

Hydroxy epoxidation of dienes.2 Photosensitized oxygenation of dienes when catalyzed by titanium(IV) isopropoxide results in an epoxy alcohol, formed by an oxygen transfer from an allylic hydroperoxide. 

Fig. 19 The competing transition states for the epoxidation of dienes and enynes...

Chiral alkenyl and cycloalkenyl oxiranes are valuable intermediates in organic synthesis [38]. Their asymmetric synthesis has been accomplished by several methods, including the epoxidation of allyl alcohols in combination with an oxidation and olefination [39a], the epoxidation of dienes [39b,c], the chloroallylation of aldehydes in combination with a 1,2-elimination [39f-h], and the reaction of S-ylides with aldehydes [39i]. Although these methods are efficient for the synthesis of alkenyl oxiranes, they are not well suited for cycloalkenyl oxiranes of the 56 type (Scheme 1.3.21). Therefore we had developed an interest in the asymmetric synthesis of the cycloalkenyl oxiranes 56 from the sulfonimidoyl-substituted homoallyl alcohols 7. It was speculated that the allylic sulfoximine group of 7 could be stereoselectively replaced by a Cl atom with formation of corresponding chlorohydrins 55 which upon base treatment should give the cycloalkenyl oxiranes 56. The feasibility of a Cl substitution of the sulfoximine group had been shown previously in the case of S-alkyl sulfoximines [40]. 

In contrast to these observations, stereoselective epoxidation has been described.265 Internal olefins reacting with a stoichiometric amount of pivalaldehyde yield quantitatively the corresponding epoxides. The higher reactivity of the internal double bond permits selective epoxidation of dienes ... 

The selective epoxidation of dienes by CPO from C. jumago has been reported (Scheme 2.23) [275]. The methacrylate was a good substrate which showed two types of selectivity only the isolated double bond was epoxidized to produce the monoepoxide in 73% yield and the conjugated a, 3-unsaturated bond of the methacrylic acid moiety was untouched. It was suggested that conjugated terminal alkenes might... 

Oxidative addition to vinyl epoxides (obtained from epoxidation of dienes) affords a ferralactone XL where E = O. This procedure tolerates a varied substitution... 

FIGURE 2.2 Regioselectivity in the epoxidation of dienes. Reactions performed at room temperature (RT) with either 2 mol% catalyst 1b in 24 h or stoichiometric amount of m-chlor-operbenzoic acid (m-CPBA) in 0.5 h. 

TABLE 2.5 Catalytic asymmetric epoxidation of dienes with hydrogen peroxide mediated by Ih... 

K. Kamata, Y. Nakagawa, K. Yamaguchi, N. Mizuno, Efficient, regioselective epoxidation of dienes with hydrogen peroxide catalyzed by [Y-SiWio034(H20)2], J. Catal. 224 (2004) 224. 

E. Brule, Y. R. de Miguel, K. K. M. Hii, Chemoselective epoxidation of dienes using polymer-supported manganese porphyrin catalysts. Tetrahedron 60 (2004) 5913. 

The epoxidation of dienes using MMPP occurs, as expected, at the more electron rich double bond, like those reactions using MCPBA. The example shown in Eq. (7) was one of the stages in a synthesis of the quinone antibiotic frenolicin and used MCPBA in the presence of 5% aqueous sodium hydrogen... 

Selectivity in the epoxidation of dienes where the two alkene residues are a widely differing nucleophilicities is not difficult to achieve and we will return to this point later in this review. However, it is worth pointing out that quite good diastereofacial selectivity was reported in the epoxidation shown in Eq. (12), part of a total synthesis of (+ )-altholactone. The epoxidation using MCPB A proceeded with poor selectivity whereas MMPP gave predominant attack on the P-face and a 3.5 1 mixture of the substituted tetrahydrofuran derivatives was obtained after acid catalysed cyclisation [26]. 

Synthesis, structures of novel manganese containing heteropolyznions, and applications in regioselective epoxidation of dienes with hydrogen-peroxide, J. Amer. Chem. Soc., 120 252 (1998). 

On the other hand (Scheme 29), epoxidation of diene 223 with MCPA afforded a mixture of four epoxides 228-231 in 5%, 36%, 22% and 8% yields, respectively. Epoxide 229 was transformed into the 1-hydroxyguaianolides 8-deoxy-l l)3,13-dihydrorupicolin B (232) and 8-deoxyrupicolin B (233), while epoxides 230 and 231 were transformed... 

K.S. Suslick and B.R. Cook, Regioselective epoxidations of dienes with... 

Burke CP, Shi Y (2006) Regio- and enantioselective epoxidation of dienes by a chiral dioxirane synthesis of optically active vinyl cis-epoxides. Angew Chem Int Ed 45 4475-... 

Sheng, M. N. Zajacek, J. G. Hydroperoxide oxidations catalyzed by metals. III. Epoxidation of dienes and olefins with functional groups. J. Org. Chem., 1970, 35,1839. 

The epoxidation of diene-based polymers is advantageous because it provides active sites along the polymer chains for further modification. Furthermore, introducing an epoxide functional group to unsaturated polymers can help improve abrasion resistance, adhesive strength, and heat stability. Epox-idized polymers can be prepared by polymerizing epoxidized monomers however, this method typically results in many side reactions. Numerous reports have focused on the epoxidation of diene-based polymers with... 

Nippon Peroxide Co. Ltd. (1982) Epoxidation of diene polymers. Japanese patent JP57117506... 

The sulfide-catalyzed enantioselective epoxidation reaction is the most extensively studied transformation in ylide catalysis, and two ylide generation methods (aUcylation/deprotonation and carbene transfer) have been developed. Compared with conventional methods for epoxidation via oxygen transfer to the carbon-carbon double bond, such as the Sharpless epoxidation, Jacobsen-Katsuki epoxidation, and Shi epoxidation, the yhde approach can be regarded as an alkyUdene transfer reaction to carbonyl groups (C=0), providing a different retrosynthetic analysis for the construction of epoxides. In particular, in the synthesis of vinyl epoxides, the ylide route has priority over conventional oxidation methods, since the issue of regjoselectivity in the epoxidation of dienes will not be present [32]. 

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