Conjugated diene complexes epoxidation

Some derivatization methods mentioned in other sections of this review include chemical ionization by nitric oxide (MS) or epoxidation (MS), formation of jr-complexes for NMR (shift agents) etc. Also, the Diels-Alder reaction, which was mentioned several times as a tool for derivatization of conjugated dienes and polyenes, was extensively described and reviewed in the literature. 

Asymmetric epoxidation of conjugated dienes and enynes catalysed by the chiral man-ganese(EI) complex 232 give monoepoxides exclusively reactions of cw-enynes give /raw.v-alkynyl epoxides as the major products with a high level of asymmetric induction362. 

In a related study, Jorgensen has examined the regio- and enantioselective catalytic epoxidation of conjugated aliphatic dienes using achiral and chiral manganese salen complexes and sodium hypochlorite or iodosylbenzene as the terminal oxidant. For most substrates, the less substituted diene is epoxidized however, in the case of isoprene, the more highly substituted double bond is the more reactive. Jorgensen proposes an intermediate of type 11, the... 

Arene oxides show the characteristic reactions of epoxides (isomerization to ketones, reductions to alcohols, nucleophilic additions, deoxygenations) and olefins or conjugated dienes (catalytic hydrogenation, photochemical isomerization, cycloaddition, epoxidation, metal complexation). Where a spontaneous, rapid equilibration between the arene oxide and oxepin forms exists, reactivity typical of a conjugated triene is also found. 

Conjugated dienes are oxidized to epoxides (or diols, if water is present) with the MTO/H2O2 system [11]. Urea/H202 avoids the subsequent epoxide ring opening. Electron-rich and conjugated dienes are more easily oxidized than electron-poor dienes and dienes with isolated double bonds. According to kinetic measurements complex 3 plays no important role as catalyst in this case. Compound 2 is an active species [11a]. 

Asymmetric epoxidation of 1,3-dienes and eynes. Jacobsen has extended his method for effecting asymmetric epoxidation of alkencs with a chiral (salen)Mn (II) complex (16, 157-158) to conjugated dienes and enynes by use of the chiral (salcn)Mn(IH) complex 2 ... 

The success of the enantioselective Sharpless epoxidation to a large extent depends on the configuration of the double bond of an available substrate. Shibasaki et al. developed an efficient method of stereospecific synthesis of exocychc double bonds using 1,4-hydrogenation of conjugated dienes catalyzed by an arene-Cr(CO)3 complex [43]. Allylic alcohol 31b [44,45], a substrate for Sharpless epoxidation, was obtained using this procedure. Alcohol... 

Since the conformations of the 11-membered ring vibsanins A and P-T, which bear a 6,7-epoxide ring, are fixed, analysis of their NMR can be performed normally. On the other hand, vibsanin B (1) and vibsanols A (23) and B (24) [18], which contain a cross-conjugated diene, show complex NMR signals due to the presence of several kinds of conformational isomers. Therefore, careful structure elucidation should be performed by a combination of VT NMR experiments and MM2 calculations [13]. 

In general, one can use a variety of oxidation techniques to form derivatives of dienes and higher polyenes for their analysis however, the information obtained with conjugated systems is muddled by the complexity of products. Also, it is obvious that since the oxidized derivatives contain different functionalities, e.g. epoxides, alcohols, acids etc., the analytical techniques employed should also be variable (see also Scheme 2). 

However, 1,2-diamino-l,2-di-(cr(-butylethane (3) holds particular interest because of its increased steric bulk and the absence of benzylic protons. Its recent ready availability should render it as attractive as the frequently used vicinal diamines 7 and 8. To our knowledge, only one application of this diamine has been previously described in the literature (eq 5), where the regio- and enantioselective epoxidation of conjugated aliphatic dienes were studied using the chiral manganese salen complex (9). 

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