Dienes and trienes

The singlet cis-trans isomerization mechanisms of conjugated olefins appear to be quite different from those of isolated olefins. 

It is probably reasonable to assume that the excited-state motion is initially dominated by the slope of the B and A surfaces, which points in the disrotatory way and toward the diagonally-bonded pericyclic funnel, and to assume that the acquired momentum is kept after the jump to Sq. This would point in the direction of bicyclobutane. Unless the surface jump occurs right at the cone tip, it generates an additional momentum in the Xj direction, that is, along the y perturbation coordinate, toward cyclobutene and the original as well as cis-trans isomerized butadiene. Whether further facile motions on 

Triplet-sensitized cis-trans isomerization is frequently more efficient. Thus, the direct excitation of 1,3-pentadiene (piperylene), which has been studied in great detail, results in cis-trans isomerization with very low quantum yields (4 ,, = 0.09, = 0.01) and very small quantities of di- 

The reaction pathways both for single- and double-bond isomerization enter the funnel region at less than one-third of the way toward the products, suggesting that the majority of excited-state molecules should decay back to the ground-state reactant. In addition, the excited-state barrier for singlebond isomerization is smaller than that for double-bond isomerization, reducing the quantum yield for cis-trans isomerization (since the product of s-cis-s-trans isomerization is just a different conformer, not a new cis-trans isomer of the reactant). Thus the low experimental value of I = 0.034 reported for the quantum yield of /ran.v-hexatriene from r/.v-hexatriene (Jacobs 

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Other advances include the construction of seven- and nine-membered rings via the analogous [4-1-3] and [6-1-3] cycloadditions with dienes and trienes respectively. Heterocycles, such as tetrahydrofurans and pyrrolidines, are accessible using carbonyl compounds and imines as substrates. The following discussion is organized around these recent discoveries. It serves to illustrate the versatility and the high degree of selectivity which are some of the distinctive features of the Pd-TMM chemistry. 

Double-bond migration often passes unnoticed, for unless tracers are employed, there may be no direct evidence remaining that migration has occurred. Nonetheless, the fact that it does occur can have a number of important consequences. Selective removal of cis homoconjugated dienes and trienes in natural oils, used to make edible hydrogenated fats, depends mainly on prior isomerization of multiple unsaturation into conjugation under hydrogenation conditions (J9). 

The oligomerization of cardanol with boron trifluoride etharate as the initiator was studied in detail by Antony et al. [171]. The reaction conditions were optimized by using gel permeation chromatography as 140°C with an initiator concentration of 1%. GPC data indicate conversion of all monoene, diene, and triene components into polymer except the saturated component, indicating participation of all the unsaturated components in polymerization. It is possible that the initiation of po-... 

Butadiene could be oligomerized to cyclic dienes and trienes using certain transition metal complexes. Commercially, a mixture of TiCU and Al2Cl3(C2H5)3 is used that gives predominantly cis, trans, trans-1,5,9-cyclododecatriene along with approximately 5% of the dimer 1,5-cyclooctadiene ... 

Note that a conjugated diene and a conjugated triene react with, opposite stereochemistry. The diene opens and doses by a conrotatory path, whereas the triene opens and closes by a disrotatory path. The difference is due to the different symmetries of the diene and triene HOMOs. 

Figure 30.7 Photochemical cyclizations of conjugated dienes and trienes. The two processes occur with different stereochemistry because of their different orbital symmetries.

The copper-catalyzed additions of sulfonyl chlorides to conjugated dienes and trienes as well as to aryl-substituted cyclic olefins and substituted styrenes have been described for example, arenesulfonyl chlorides add to vinylarenes providing good to excellent yields of )S-chlorosulfones ... 

Coupled LC-LC can separate high-boiling petroleum residues into groups of saturates, olefins, aromatics and polar compounds. However, the lack of a suitable mass-sensitive, universal detector in LC makes quantitation difficult SFC-SFC is more suitable for this purpose. Applications of multidimensional HPLC in food analysis are dominated by off-line techniques. MDHPLC has been exploited in trace component analysis (e.g. vitamin assays), in which an adequate separation for quantitation cannot be achieved on a single column [972]. LC-LC-GC-FID was used for the selective isolation of some key components among the irradiation-induced olefinic degradation products in food, e.g. dienes and trienes [946],... 

The reaction of benzyne with cyclohexadiene has been known for some time 4>, but although a number of steroidal cis-dienes are readily available no reactions with arynes had been reported prior to our beginning such investigations 145>. This was somewhat surprising in view of the number of reports concerning the modification of steroids by means of reactions with carbenes 146 i49) and the known Diels-Alder reactions of steroidal dienes and trienes iso.isi). 

The presence of the C15 saturated chain displayed an efficient gelling ability in a wide range of organic solvents, water, and protic solvent mixtures (1 1), whereas the unsaturated derivatives (mixture of four molecules) formed fibrous nanostructures as opposed to stronger gels. The diene and triene components of the cardanyl glycosides in their fully hydrated state formed fluid nanostructures at room temperature and could not self-assemble to form gels. 

Alkadiene and alkatriene => diene and triene alkadiyne and alkenyne => diyne and enyne. 

Polyunsaturated (dienes and trienes) lipids found in sediments have been proven to be valuable tools in the determination of palaeo-water temperatures616-18. These C20, C25 and C30 highly branched isoprenoids were investigated analytically by all the tools suggested in this review. We will select one diene to demonstrate the use of the MS, oxidation (bis-epoxidation) MS and H NMR techniques previously discussed. This diene, 2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)pentadec-5-ene (4), shows the fragmentation pattern given in Scheme 2. 

Chemical and other physical methods of ionization were also employed for the structural determination of dienes and polyenes. Such is the case for the recent investigation of aliphatic dienes and trienes by chemical ionization with nitric oxide (NO+)25. It has been known since 1975 that olefins can be chemically ionized by NO+ [CI(NO)]26. Two distinct processes may apparently occur (i) electrophilic addition of NO+ to the ene leading to [M + NO]+ ion and (ii) an oxidative cleavage (possibly catalysed by the... 

Cycloaddition with nitrile oxides occur with compounds of practically any type with a C=C bond alkenes and cycloalkenes, their functional derivatives, dienes and trienes with isolated, conjugated or cumulated double bonds, some aromatic compounds, unsaturated and aromatic heterocycles, and fullerenes. The content of this subsection is classified according to the mentioned types of dipolarophiles. Problems of relative reactivities of dienophiles and dipoles, regio- and stereoselectivity of nitrile oxide cycloadditions were considered in detail by Jaeger and... 

In addition, a number of related dienes and trienes (Scheme 30.4) were hydrogenated with catalyst 90, with promising results. 

To complete the range of geometric isomers of terminal and non-terminal dienes and trienes available, systems nominally derived from inaccessible (Z)-alkenylzirconocenes are desirable. Fortunately, insertion of the various carbenoids discussed above into mono- or bis(alkynyl) zirconocenes 64 and 65 affords dienyne products 66 [38], which are readily reduced to the desired ( ,Z,2)-trienes (Scheme 3.15) [45—47]. Insertion of the f5-alkynyl carbenoid 62 allows a convenient access to (Z)-enediynes 67. 

Figure 7.9 Electrocyclic processes of a diene and triene by photochemical and thermal pathways...

Explain the ideas relating to frontier orbitals when considering the stereochemistry of the electrocyclic reactions of dienes and trienes. 

Recent theoretical and spectroscopic studies indicate that in aliphatic dienes and trienes, excitation to the spectroscopic l1 state usually results in facile twisting about the termini in the stereochemical sense dictated by orbital symmetry selection rules for the appropriate electrocyclic ring closure, motions which are often accompanied by some degree of planarization of the carbon framework. In general, relatively minor distortions... 

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