E-Trienes

The conjugated (E,E,E) triene part of rapamycin 341 has also been constructed by the intramolecular coupling of the (E,E) iododiene with the (E) vinylstannane in 340 in 75% yield [160],... 

Chapter 19 by Bartelt is devoted to the pheromonal role of short-chain hydrocarbons, especially short i n etli y l/etli y I - branched and unsaturated components in beetles. The most abundant components in Carpophilus hemipterus (Coleoptera, Nitidulidae) have been identified as (2/ ,4/ ,6/ ,8/ )-3,5,7-(rimc(hyl-2,4,6,8-decatetracnc and (2E,4E,6E,SE)-3,5,7-trimethyl-2,4,6,8-undecatetraene (Bartelt et al., 1990). Later studies showed that male C. hemipterus emit nine all-E tetraene hydrocarbons and one all-E triene hydrocarbon in addition to the two previously reported pheromonally active tetraenes (Bartelt et al., 1992). In their review of biologically active compounds in beetles, Francke and Dettner (2005) fisted only a few dozen of those pheromonal compounds, most of which were identified by Bartelt. 

P.F. (2005) Accumulation of an E,E,E-triene by the monensin-produdng polyketide synthase when oxidative cydization is blocked. Ar ewandte Chemie-International Edition, 44,... 

Z, E)-Trienes. Lindlar hydrogenation of substituted diene acetylenic esters of type 1-3 affords the corresponding (Z,E,E)-triene esters in high yield. The site selectivity of this reduction is excellent for all substrates examined except 3 evidently the steric bulk of the isopropyl or methyl substituents of 1 and 2 suppresses the rate of butadiene reduction in these systems. Only cis C2-C3 double bonds are obtained. 

The last example illustrates use of this elimination as a route to an almost pure conjugated (E,Z,E)-triene. 

Intramolecular Diels-AUer reactions of trienes.9 0 The thermal cyclization of the (E,E)-triene 1 affords trans- and cis-perhydroindenes 2 and 3, with a slight preference for the former isomer. The reaction is markedly catalyzed by Lewis acids such as A1C13, C2H5A1C12, and TiCl4, and results in cyclization exclusively to the... 

Biomimetic studies of this proposed cascade have provided further tantalising, albeit incomplete, supporting evidence [81]. Feeding studies with a NAC thioester of the required (E,E,E)-triene intermediate 42 in labeled form have so far been unsuccessful, although this may well be due to problems of transport across the cell membrane and degradation by p-oxidation pathways [82]. 

More recently an alternative biosynthetic pathway has been proposed by Townsend and Basak (Scheme 22) [83]. This alternative model involves the iterative syn-oxidative cyclization of a (Z,Z,Z)-triene intermediate 44 in contrast to the (E,E,E)-triene intermediate 42 of the epoxide cascade mechanism. The putative, alkoxy-linked, non-heme metal-oxo species 45 undergoes a [2-1-2] cycloaddition to yield the metalloxetane intermediate 46. Reductive elimination then results in an overall syn-addition of the two oxygen atoms 47. Oxidation of the metal intermediate 47 to 48 and two further [2 + 2] cycloaddition-reductive elimination-metal oxidation cycles would result, after final hydroxylation, in monensin A 41. 

Reductive elimination. All (E) trienes are formed by treatment of 1,6-diben-zoyloxy-2,4-dienes with the low-valent titanium species prepared from TiClj and LiAlH4. This method is applicable to the synthesis of a leukotriene. 

For 2-methyl-E-hexatriene (cmax 43,000 ref. 68) the results are summarized In Figure 13. It appears that while the Z-Isomer is the major primary photoproduct, the methylvinylcyclobutene also is formed directly from the photoexclted E-triene. Other products, methylbicyclo[3.1.0]hexene and methyl-1,2,4-hexatrlene, are formed only after a certain time lag during which the proportion of methyl-Z-hexatrlene has Increased to an appreciable level. 

Many examples of the use of this strategy with KHMDS has been reported to construct double bonds in the total synthesis of natural products. For instance, the E,E,E-triene of thiazinotrieno-mycin E was constructed according to this process in 85% yield and with 10 1 selectivity (eq 57). ... 

It is known that the photochemical reaction E26.I.I is not a straightforward sequential reaction leading to the final product (3). As the photoreaction of (I) progresses, photons are also absorbed by the previtamin (2) giving the undesirable trans isomeric E-triene,... 

The formation of the hexalin was envisioned to occur via the Z-triene although a direct ring expansion could not be ruled out. The E-triene also rearranged to the cyclohexadiene most likely via formation of a vinylcyclobutene although direct geometric isomerization was not ruled out. 

When using the cyclopentene as a starting cycloolefin, equilibrium stereo-content of cometathesis products is achieved at incomplete cyclopentene conversion. Equilibrium concentration of 1,6E-undecadiene is 86 % and of 1,6E,1 lE-hexadecatriene (the product of double insertion of cyclopentene into 1-hexene) - 87 %. At the same time, in the case of initial C7-C10 cycloolefins thermodynamically equilibrium values for corresponding 1,AE-dienes (A= 8-11) are 84 % and for corresponding 1,(8-11)E,( 15-21 )E-trienes are 78 % (Table 2). 

Poly(vinyl acetate) (3.38) undergoes simultaneous chain scission and cross-linking when UV irradiated (254 nm). At the same time its absorption spectrum (Fig. 3.23) shows the formation of short sequences of conjugated double bonds, i.e. trienes. 

Fattorusso, E Magno, S Mayol, L., Amico, V., Oriente, G., Piatlelh, M and Tringali, C. (1978) Isolation of (2S,8R)-germacra-l(ll)5(12)E-trien-2-ol acetate from the brown alga Dilophus Juscida. Tetrahedron Lett.. 19,4149-4152. 

Solladie, G., Colobert, F., and Stone, G.B. (1995) A short and easy route to conjugated all-E-trienes and tetraenes. Application to the synthesis of navenone and lignarenone B. Synlett, 1135—1137. 

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