A,w-dienes

Other commercially relevant monomers have also been modeled in this study, including acrylates, styrene, and vinyl chloride.55 Symmetrical a,dienes substituted with the appropriate pendant functional group are polymerized via ADMET and utilized to model ethylene-styrene, ethylene-vinyl chloride, and ethylene-methyl acrylate copolymers. Since these models have perfect microstructure repeat units, they are a useful tool to study the effects of the functionality on the physical properties of these industrially important materials. The polymers produced have molecular weights in the range of 20,000-60,000, well within the range necessary to possess similar properties to commercial high-molecular-weight material. 

Carbonylation-Decarbonylation. These reactions constitute a large and important segment of the homogeneous catalytic literature. Catalysis by most of the group VIII noble metals has been found, and a variety of substrates have been converted. For example, olefins react with CO and PdCl2 or (< 3P)2PdCl2 to yield -chloroacyl chlorides (58) and unsaturated acyl chlorides (59), respectively, a, w-Dienes, such as... 

Gohlke, F., Lohse, A.W., Dienes, H.P, Lohr, H., Marker-Hermann, E., Gerken, G., Meyer zum Buschenfelde, K.-H. Evidence for an overlap syndrome of autoimmune hepatitis and primary sclerosing cholangitis. J. Hepatol. 1996 24 699-705... 

The elimination of ethylene (the monomer) is not favored energetically, and pyrolysis of polyethylene does not occur as an unzipping process. Dienes are formed during pyrolysis by the same process as described above, with an a-olefin undergoing the cleavage followed by the radical disproportionation with the formation of an a,w-diene. 

The cross-metathesis between an acyclic and a cyclic alkene, nowadays called ring-opening metathesis (ROM), provides a convenient route to certain polyunsaturated compounds. For example, ethenolysis of cycloalkenes yields a,w-dienes (eq. (6)), which may be useful, e. g., as crosslinking agents in polymers and as precursors for a, -difunctional compounds [13],... 

Transition metal-catalyzed cycloisomerizations of a,w-dienes providing atom-economical routes to various carbo- and heterocyclic compounds 12CRV4736. 

Reaction of n-butylthiocyclooctene (5b) with ethylene (7) in the presence of 1 leads to the sulfur a,w-diene 12 (Scheme 8). A decrease of the initial 5b/l molar ratio leads to an increase of the final conversion of 5b, while an increase of the initial 7/5b molar ratio gives, as expected, a higher yield of 12 (Table 5). High reaction temperatures drastically enhance the turnover rates. 

Figure 237 PESs for RCM of simple a,w-dienes numbers in the legend refer to the final ring size (cyclopentene to c/s-cyclodecene). ...

The achiral triene chain of (a//-rrans-)-3-demethyl-famesic ester as well as its (6-cis-)-isoiner cyclize in the presence of acids to give the decalol derivative with four chirai centres whose relative configuration is well defined (P.A. Stadler, 1957 A. Escherunoser, 1959 W.S. Johnson, 1968, 1976). A monocyclic diene is formed as an intermediate (G. Stork, 1955). With more complicated 1,5-polyenes, such as squalene, oily mixtures of various cycliz-ation products are obtained. The 18,19-glycol of squalene 2,3-oxide, however, cyclized in modest yield with picric acid catalysis to give a complex tetracyclic natural product with nine chiral centres. Picric acid acts as a protic acid of medium strength whose conjugated base is non-nucleophilic. Such acids activate oxygen functions selectively (K.B. Sharpless, 1970). 

Dichlorodisulfane, UV spectrum of, 16 311 a,w-Dichloro-oligosilane, 42 221 Dichlorofprotoporphyrin IX)tin(IV), 36 14-15 Dichlorosilylene, 29 6-15 action reactions, 29 12-15 with alkynes, 29 12-13 with conjugated dienes, 29 13... 

A single alkyne relay is involved in the cascade oligocyclizations of 2-bromoalka-l,w-diene-//-ynes such as 90, 92, 94 and others. Three new rings are formed in these sequences of two intramolecular Heck-type reactions and a 67r-electrocyclization leading to various oligocyclic systems such as 91, 93, 95 in a rather elegant way (Scheme 25). - ... 

NaOH-HiOz) or to carboxylic acids (with w-chloroperbenzoic acid).-190 Double bonds can be hydroborated in the presence of triple bonds if the reagent is 9-BBN.191 On the other hand, dimesitylborane selectively hydroborates triple bonds in the presence of double bonds.192 Furthermore, it is often possible to hydroborate selectively one particular double bond of a nonconjugated diene.191 When the reagent is catecholborane, hydroboration is catalyzed by rhodium complexes, such as Wilkinson s catalyst.194 Enantioselective hydro-boration-oxidation has been achieved by the use of optically active rhodium complexes.195... 

Finally, a bis(azomethine)-azomethine isomerization has been reported for perfluorinated a,w-bis(azomethines)28 which resembles the isomerizations of perfluorinated a.ro-dienes discussed in Section 5.1.2.3. Perfluoro-2,4-diazapenta-l,4-diene (43) and perfluoro-2.5-diazahexa-l,5-diene (45) rearrange completely with cesium fluoride to the internal azomethine isomers 44 and 46. respectively. In the case of perfluoro(3.4-dimethyl-2.5-diazahexa-l.5-diene) (47). the expected double-bond-migration product 48 is accompanied by cyclic product 49, which suggests a reaction mechanism involving addition of a fluoride ion to form a nitrogen anion, as opposed to a concerted SN2 -mechanism. 

Foster S. P. and Roelofs W. L. (1990) Biosynthesis of a monoene and a conjugated diene sex pheromone component of the light brown apple moth by Ell-desaturation. Experientia 46, 269-273. 

The reaction of 1,3-dibromopropene with carbonyl compounds mediated by indium in water gives 3,3-disubsti-tuted propene 63 (Scheme 55). In the formation of 63, 1,3-dibromopropene acts as a w-allyl dianion synthon. Aromatic aldehydes generally have a higher selectivity than aliphatic ones in the product formation. Unsubstituted and electron-withdrawing group-substituted benzaldehydes give mainly 3,3-disubstituted propene 63. For electron-rich benzaldehydes, the formation of both 3,3- 63 and 1,3-disubstituted propene 64 is dramatically decreased and the selectivity is reversed completely to give diene 65 and homoallylic alcohol 66.219... 

Carruthers W. A. In Cycloaddition Reactions in Organic Synthesis-, Pergamon Oxford, 1990 Fringuelli, F. Taticchi A. In Dienes in the Diels Alder Reaction, Wiley New York, 1990. 

The complexes W( " -diene) (CO)6-2 (n = 2, diene = 1,3-butadiene, (83) n = 3, diene = 2,3-dimethylbutadiene, 84) have been prepared, and their solid-state molecular structures have been determined. Interestingly, the two diene ligands in (83) are twisted relative to one another, imparting C2 symmetry to the complex. Homoleptic (84) lias been the subject of a detailed theoretical investigation in an attempt to explain its rare trigonal-prismatic coordination... 

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