A,<y-Dienes

This access to a , y-bis(tricyclohexyltin)alkanes proves to be very convenient when the corresponding organic dihalides are available. When this is not the case, and when a , y-dienes are more easily accessible, a double hydrostannation of these unsaturated compounds can be used. As indicated above, this radical addition has to be conducted in less mild conditions than for the addition of tri-n-butyltin hydride, for instance, because of the bulkiness of the organotin center and also of the more nucleophilic character of the tricyclohexyltin radical. Nevertheless, the treatment of 4,4 -di(butenyl)biphenyl or 4,4 -bis(but-3-enyloxymethyl)biphenyl with tricyclohexyltin hydride at 130 °C over seven days affords the corresponding adducts 72 and 75 in good yields (Scheme 3.7.11). Due to its rapid decomposition at this temperature, the AIBN initiator has to be added in small portions for the duration of the reaction. 

As mentioned in the section Long-Chain Branching, the presence of low levels of a , y-dienes in the reaction mixture for ethylene polymerization can lead to polyethylene with LCB or cross-linked PE. 

What accounts for the stability of conjugated dienes According to valence bond theory (Sections 1.5 and 1.8), the stability is due to orbital hybridization. Typical C—C bonds like those in alkanes result from a overlap of 5p3 orbitals on both carbons. In a conjugated diene, however, the central C—C bond results from conjugated diene results in part from the greater amount of s character in the orbitals forming the C-C bond. 

The synthesis of the C(17)-C(24) segment also began with a diastereoselective boron enolate aldol addition. The adduct was protected and converted to an aldehyde in sequence H. The terminal diene unit was installed using a y-silylallyl chromium reagent, which generates a (3-hydroxysilane. Peterson elimination using KH then gave the Z-diene. 

Several strategies closely related to the Peterson synthesis have been developed for diene and polyene generation. Angell, Parsons and coworkers reported a mild method for the diene installation on a carbonyl group using a y-bromoallylsilanc reagent in the presence of excess chromous chloride and a catalytic amount of nickel(II) chloride (equation 102)180. 

INAS reactions of carbonates of 3,5-dienyl alcohols (i. e., involving a conjugated diene moiety) [72] and 3,4-dienyl alcohols (i. e., having an allene moiety) [73] also proceed smoothly to furnish the corresponding (3,y-unsaturated esters. The reaction of 4-silyl- or 4-stannyl-3,4-dienyl carbonate having axial chirality proceeds with excellent chirality transfer, as exemplified in Eq. 9.39, thereby affording a novel access to optically active a-substituted p.y-unsaturated esters [73],... 

The product is a y,8-unsaturated carbonyl compound (a 1,5-diene), hinting that the last step is a Claisen rearrangement. 

Synonyms Biethylene Bivinyl Butadiene Buta-1,3-diene a.y-Butadiene Butadiene monomer CCRIS 99 Divinyl EINECS 203-450-8 EINECS 271-039-0 Erythrene NCI-C50602 Pyrrol-ylene UN 1010 Vinylethylene. 

The unsaturated molecule Y may be carbon monoxide, an olefin, a conjugated diene, an acetylene, a carbonyl compound, various unsaturated carbon-nitrogen compounds, or probably any of several other unsaturated materials. The reactive part of the covalent metal compound is usually a metal-hydrogen, metal-carbon, metal-oxygen, metal-halogen, metal-nitrogen, or metal-metal group. This reaction... 

A recently described method for insertion of a carbon monoxide molecule into the monoepoxide of a conjugated diene gives /3-lactones in high yield. This is achieved by reaction of iron pentacarbonyl with the starting vinyloxirane to give the 7r-allyl iron complex (66), which on oxidation with cerium(IV) ammonium nitrate gives the /3-lactone. In some cases, y-Iactone products can also be obtained from this reaction (8lJCS(Pi)270). 

With an a, y-ketodiol, cyclization to produce a 3-furanone derivative is feasible, as is shown for the synthesis of ascofuranone (71) and geiparvarin (72) (Scheme 6.57) (286). The precursor for 71 was prepared by the cycloaddition of diene 66 to nitroalcohol 67. In this case, regioselective attack occurred only on the terminal double bond. Reductive cleavage-hydrolysis of the isoxazoline adduct 68 with Mo(CO)6 followed by acid-induced cyclization led to the furanone intermediate (286). A similar strategy was used for the synthesis of geiparvarin (72) (Scheme 6.58) (286). 

Hydrosilation of an alkenylsilane in the presence of a catalyst provides a route to five-, six- and seven-membered rings but is of little use for the smaller ones. Tin-substituted cyclohexa-2,5-dienes result directly from the a,[Pg.575]

Electron withdrawing substituents such as aldehyde or imonium functions at the other end of the alkene or the 1,3-diene transform enamines and 1,3-dienamines into push-pull systems characteristic of dyes. Electron release (push) of the donor group shields the / , S, e,... carbons and electron withdrawal (pull) of the acceptor group (carbonyl oxygen or imonium nitrogen) deshields in the a, y,... position [343],... 

Dienes.1 Allylic esters such as 2 can be converted into a 1,5-diene (5) by methylenation with 1 to give an allylic vinyl ether (3). Claisen rearrangement of 3 results in a y,<5-enone 4, which is converted to the desired diene (5) by a second methylenation with 1. Actually, this thrce-stcp process can be carried out without... 

Nakamura, H., Kobayashi, J., and Ohizumi, Y., Novel bisabolene-type sesquiterpenoids with a conjugated diene isolated from the Okinawan sea sponge Theonella cf. swinhoei, Tetrahedron Lett., 25, 5401, 1984. 

Some polyunsaturated fatty acids were tested for the production of hydroxy fatty acids by PR3 because polyunsaturated fatty acids contained a, 4-ds,cis-diene unit which could serve as a key structural element for the hydroxylation by lipoxygenase. When eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) carrying l,4-d c y-diene unit were used as substrates for bioconversion by PR3, new products were detected on TLC analysis as shown in... 

Interestingly, the role of methyl toms-2,4-pentadienoate changes from that of a diene, in its reaction with enamines,29 to a y,(5-dienophile in its reaction with dienamines32 (Scheme 18). 

These have previously been obtained by electrophilic attack on ene-yl complexes [equation (a) Y = CH(C02Me)2, OMe ch = 1J-C5H5 diene = 1,5-cyclooctadiene]1 or by reaction of the compounds (diene)MBr2 with 57-C5H6Fe(CO)2Br (diene = 1,5-cyclooctadiene or 1,2,3,4-tetraphenyl-l,3-cyclobutadiene).2 An example of the former method is given in which the methoxy-cyclooctenyl derivative is used as the substrate and tetrafluoro-boric acid as the electrophile. The substrate is conveniently prepared and used without isolation, and in this way the reaction takes only a few hours, starting with dichloro(l,5-cycloocta-diene)palladium, prepared as described above. 

SYNS BIETHYLENE BIVINYL BUTADIEEN PUTCH) BUTA-1.3-DIEEN pUTCH) BUTADIEN (POLISH) BUTA-1,3-DIEN (GERMAN) BUTA-1,3-DIENE a-Y-BUTADIENE DIVINYL ERYTHRENE NCI-C50602 PYRROLYLENE VINYLETHYLENE... 

BUTADIENE see BOP500 BUTA-1,3-DIENE see BOP500 a-Y-BUTADlENE see BOP500 BUTADIENE DIEPOXIDE see BGA750... 

The addition of one mole of H2 to cyclohexene releases -28.6 kcal of energy (liquation [1]). If each double bond is worth -28.6 kcal of enei y, then the addition of two moles of H2 to 1,3-cyclohexadiene (Equation [2]) should release 2 x —28.6 kcal = -57.2 kcal of energy. The observed value, however, is -55.4 kcal/mol. This is slightly smaller than expected becau.se 1,3-cyclohexadiene is a conjugated diene, and conjugated dienes are more stable than two isolated carbon-carbon double bonds. 

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