Hexa-1,4-dienes, synthesis

Azabicyclo[2.2.0]hexa-2,5-diene, pentakis-(pentafluoroethyl)-synthesis, 2, 304 2-Azabicyclop.2.0]hexadiene reactivity, 7, 360 thermal isomerization, 7, 360 2-Azabicyclo[2.2.0]hexa-2,5-diene synthesis, 2, 304 1 -Azabicyclo[3.2.0]hexadiene synthesis, 7, 361 1 - Azabicyclo[2.2.0]hexane reactions, 7, 344 ring strain... 

M. C. Baird and Q. Wang. Synthesis of polymers of vinyl ethers, 1,5-hexa-diene and A-vinylcarbazole. US Patent 5 439 996, assigned to Qneen s University at Kingston (Kingston, CA), August 8, 1995. 

Another commercially important reaction is du Font s synthesis of 1,4-hexa-diene. This is converted to synthetic rubber by copolymerization with ethylene and propylene, which leaves the polymer with unsaturation. Unsaturation is also present in natural rubber, a 2-methylbutadiene polymer 12.13, and is necessary for vulcanization. 

Four manufacrnred pesticides and two pesticides currently not manufactured use a priority pollutant diene as a raw material. The basic material for all six pesticides is hexa-chlorocyclopentadiene (HCCPD). The priority pollutant hexachlorobutadiene is suspected to be present in the pesticide wastewater because it is a byproduct of HCCPD synthesis and is used as a solvent in manufacturing mirex. 

The product diacid has served as starting material for the synthesis of tetracycio[7.2.1.0 . 0 ]dodeca-2,7-diene-5,12-dione, C g-hexa-quinacene, (Cj)-Ci7-heptaquinane derivatives, the parent dodecahedrane mol ecu e, and a number of substituted dodecahedranes. ... 

Intramolecular [2 + 2 + 2] cycloadditions belong to the same type of valence isomerization as those of 1,5-unsaturated compounds to cyclobutanes.70 The cobalt-mediated cyclization of l-en-5-ynes stereoselectively converts enediynes directly to bicyclo[4.2.0]hexa-l,3-dienes, as single diastereomers, when a stoichiometric amount of dicarbonyl(cyclopentadienyl)cobalt is used. This cyclization90 has a high efficiency (92%). An example is the synthesis of the protoilludane framework 23 from the enediyne precursor 22.71... 

The reaction of isobutene with hexa-1,5-diene catalysed by Re207/Al2C>3/Bu4Sn at 40 °C gives >20% yield of 6-methylhepta-l,5-diene, an intermediate in the synthesis of... 

The symmetrical Wurtz coupling has been found to give particularly good yields in the case of the higher alkane homologues. Selected illustrative examples (hexane, octane, decane and dodecane) are to be found in Expt 5.7. A related reaction is to be found in the synthesis of hexa- 1,5-diene (Expt 5.7, cognate preparation), which illustrates the symmetrical coupling of two molecules of allyl iodide by the action of sodium metal. 

Monolayered cyclophane complexes of type 263 are also reduced by sodium bis(methoxyethoxy)aluminum hydride (Red-Al) to give (i74-diene)-(i76-cyclophane)ruthenium(0) complexes (Scheme 33). If the benzene ring of 263 (arene = benzene) is converted to the (1,3-cyclohexadiene)-ruthenium(O) derivative 271, however, when the corresponding rj6-hexa-methylbenzene is reduced with Red-Al, the product is the (if-1, 4-cyclohexadiene)ruthenium(0) complex 288. Synthesis of 271 can... 

Alkenylboron compounds couple with the representative organic halides or triflates (Scheme 28). Hexaalkylbenzene was synthesized by sixfold alkenylation (55) of hexabromobenzene followed by catalytic hydrogenation of the double bonds 11521. The reaction of 1-alkenylborane with 1-bromo-l-alkyne stereose-lectively provided ( )-enyne (56) which was then converted into ( ,Z)-hexa-deca-10,12-dienal, a sex pheromone of the melonworm 11531. Due to the difficulty of purification of a geometrical mixture, the stereoselective synthesis is critical for such dienes or trienes. The PGEi derivatives (57) were synthesized... 

Although acyclic dienes in general gave a lower yield than the cyclic ones, the 1,4-stereocontrol obtained for internal conjugated dienes is of interest in synthesis. For example, E,E) and ( , Z)-hexa-2,4-dienes were stereoselectively transformed to the d,l and meso-1,4-diacetate, respectively vide infra). 

The synthesis of hexa-1,4-diene has been achieved by the nickel-catalyzed homogeneous addition of ethylene to butadiene. The nickel is introduced in the form of the complex Ni[P(OEt)3]4. The reaction is carried out in acid media, and the active catalyst is the cationic complex NiH[P(OEt)3]3 which is a 16-electron molecule. In Fig. 7 the sequence of reactions that leads to the catalytic formation of isomeric hexadienes is... 

Fig. 7. Catalytic synthesis of hexa-1,4-diene from ethylene and butadiene.

The preparation of mono- and diadducts 5 and 6, respectively, of dibromocarbene with cyclo-hexa-1,4-diene is described. The synthesis of the diadduct encounters difficulties in its isolation, due to the formation of an emulsion and polymeric products. Such problems occur occasionally if an alkene is allowed to react with bromoform under phase-transfer catalysis conditions. 

The second Tsuji synthesis, which appeared (see Scheme 1.6) in the latter part of 1978, employed a strategy similar to his earlier work for construction of the basic carbon framework. Ketal diene 19 was transformed to halo alcohol 22 by the use of chemistry established in his previous synthesis. Acylation with phenylthioacetyl chloride readily afforded ester 23. Intramolecular alkylation resulting in ring closure was brought about by deprotonation with sodium hexa-methyldisilazane to give lactone 24 in 71% yield. Synthetic 1 was then obtained in 90% yield following Raney nickel reduction. 

In view of the successful palladium-catalyzed [2 + 2 + 2] assembly of a cyclo-hexa-1,3-diene derivative from one molecule of norbornene and two molecules of /i-bromostyrene [30 a], a rationally designed synthesis of dihydrotrifoliaphane 33 as a precursor to 29 appeared to be plausible. However, when a 1 2 mixture of [2.2]paracyclophane-l-ene (32) and its 1-bromo derivative 4 was subjected to the reported conditions, the novel hydrocarbon 34 with a different array of three [2.2]paracyclophane units was obtained in 62% yield [30b]. Trifoliaphane 29, arising from oxidation of the primarily formed dihydro derivative 33, was obtained as a minor by-product (2 % yield) in this coupling. The constitution of 34 was established by an X-ray crystal structure analysis. 

Alder reaction, catalysed by dimethylaluminium chloride, has been employed in a new total synthesis of pseudomonic acids A and C from hexa-1,5-diene. In a further study of the ionophore antibiotic lasalocid (3), it has been subjected to Mannich and Baeyer-Villiger reactions. The former took an unusual course in that the carboxyl was replaced by an aminomethyl group. The natural ionophore X-14547A (4) has been synthesized from two separately prepared segments (5) and (6) of the molecule. ... 

Permanganate- and perruthenate-promoted oxidative cyclization of hexa-1,5-dienes are usually key steps in the total synthesis of naturally occurring molecules containing tetrahydrofuran rings <04JOC3368>, <04SL1437>, <04TL303>. 

Electrocycylic ring closure combined with Diels-Alder addition has been employed to derive all four rings of the tetracyclic ring system in the steroids by means of a one pot synthesis (ref.198). Thus, from the triflate of hex-4-ynol and the readily available hexa-1,5-diyne a triyne intermediate was obtained which with chromium or tungsten hexacarbonyl formed a triyne carbene complex. This with a 1,3-dialkoxybuta-1,3-diene in acetonitrile with carbon monoxide 0 atmosphere) initially at ambient temperature and then at 110°C over 24 hours afforded a 62% yield of the two products shown [(1) R = TBS (2) R = H, (1) (2) 5 2]. 

Metathesis technology enables the synthesis of many other high-purity olefins for the speciality chemicals market. Phillips have produced multi-ton quantities of hexa-1,5-diene via ethenolysis of cyclooctadiene and cyclododecatriene over a W03/Si02 catalyst reaction (9). High yields of deca-1,9-diene can be obtained from ethenolysis of cyclooctene (obtained by partial hydrogenation of readily available cyclooctadiene), reaction (10). Similarly, tetradeca-1,13-diene can be obtained via ethenolysis of cyclododecene (obtained from cyclododecatriene) (Banks 1982, 1984a). 

Natural Cyclopropanes.—The synthesis of a 2 3 mixture of cis-and tra 5-isomers of racemic ethyl chrysanthemate by addition of ethyl diazoacetate to 2,5-dimethyl-hexa-2,4-diene in the presence of copper powder was first reported in 1924. Aratani et al. have now shown that when the addition is carried out with 1-menthyl diazoacetate in the presence of the chiral (R) copper complex (17), an asymmetric synthesis can be effected leading to a 72 28 mixture of trans-[90% (-l-)-enantiomer] and ci s-[60% (-H )-enantiomer] isomers. Two interesting and new... 

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