2.4.6- Octatrienic acid

As another route, formation of 1,3,7-octatriene (7) proceeds at higher temperature in the absence of nucleophiles by Pd-catalyzed elimination of acetic acid or phenol via a 7r-allylpalladium complex from their telo-mers[l4,17]. 

Carboxylic acids react with butadiene as alkali metal carboxylates. A mixture of isomeric 1- and 3-acetoxyoctadienes (39 and 40) is formed by the reaction of acetic acid[13]. The reaction is very slow in acetic acid alone. It is accelerated by forming acetate by the addition of a base[40]. Addition of an equal amount of triethylamine achieved complete conversion at 80 C after 2 h. AcONa or AcOK also can be used as a base. Trimethylolpropane phosphite (TMPP) completely eliminates the formation of 1,3,7-octatriene, and the acetoxyocta-dienes 39 and 40 are obtained in 81% and 9% yields by using N.N.N M -tetramethyl-l,3-diaminobutane at 50 in a 2 h reaction. These two isomers undergo Pd-catalyzed allylic rearrangement with each other. 

Phenyl-1,4-hcxadicnc (122) is obtained as a major product by the codimerization of butadiene and styrene in the presence of a Lewis acid[110]. Pd(0)-catalyzed addition reaction of butadiene and aiiene (1 2) proceeds at 120 C to give a 3 1 mixture of trans- and c -2-methyl-3-methylene-l,5.7-octatriene (123)[lll]. 

Unsubstituted benzobicyclo[2.2.2]octatriene 76a bearing two methoxycarbonyl groups at the and C3 positions exhibited strong anti preference (with respect to the benzene moiety) with two oxidative electrophilic reagents, m-chloroperbenzoic acid (mCPBA) and osmium tetroxide. 

The reaction has been improved to a satisfactory process by modifying the reaction conditions. A remarkable effect of the addition of amines on the reaction was observed (49). For example, the reaction of butadiene (4 moles) and acetic acid (4 moles) in the presence of 2-(N,/V-dimethyl-amino)ethanol (4 moles) using Pd(acac)2 (3 mmoles) and PPh3 (3 mmoles) at 90°C gave complete conversion after 2 hours. The product was found to consist of 8-acetoxy-1,6-octadiene (47) (71%), 3-acetoxy-1,7-octadiene (48) (21%) and 1,3,7-octatriene (16) (8%). Various tertiary amines, such as triethylamine, )V-methylmorpholine, Af,Af,N, N -tetramethyl-1,3-bu-tanediamine, and triethylenediamine, showed the same favorable effect. Other basic salts, such as sodium and potassium acetate, accelerate the reaction, especially at high concentrations (50, 51). The selection of solvents is also important. Arakawa and Miyake found that electron-donating type solvents (e.g., THF and triethylamine) are good solvents... 

Few studies have been carried out on the telomerization of carboxylic acids other than acetic acid. Carboxylic acids are expected to react similarly with butadiene. The exception is formic acid No telomerization takes place, as described before (33, 34), and it behaves as a reductant rather than a nucleophile, forming 1,6- and 1,7-octadienes and octatriene. 

Octatriene reacts further with butadiene in acetic acid by using 7r-allylic palladium complex as catalyst to give a mixture of acyioxydo-decatrienes (54). 

Starting from 2,4,6-octatriene and pivaldehyde, the conjugated homoallylic alcohol 8 is obtained as the sole product. Cycloheptatriene-derived complexes react with aldehydes and C02 to afford mixtures of the isomeric 1,3- and 1,4-cycloheptadienyl carbinols or acids, respectively. Interestingly, analogous reactions with methyl chloroformate or dimethyl carbamoyl chloride produce the conjugated dienyl ester 9 or amide 10 as unique products [19,20]. 

Recently the group of D. W. Armstrong exploited the enantiopure ionic liquid 76 in the photoisomerization of dibenzobicyclo[2.2.2]octatrienes, and up to 12% ee was reported (Scheme 83). The obtained ee was possible due to the addition of base in order to deprotonate the carboxylic acid function of 74 resulting in a strong anion-chiral cation interaction. In the absence of a base, lower values of ee were obtained, and in the case that ester functions instead of carboxylic acid groups were present in the molecule, only racemic product was found. Ionic liquid 77 gave up to 6.8% ee. 

Generally, octatriene formation is favored by higher temperatures, higher phosphine and/or butadiene concentrations and, importantly, by an increase in steric bulk of either the ligand or the nucleophile. Indeed, Harkal et al. showed a selectivity switch from telomerization products to 1,3,7-octatriene formation by altering the steric demand of the /V-heterocyclic carbene ligand in the reaction of butadiene with isopropanol under further identical reaction conditions [48]. For the more basic nucleophiles, such as the alcohols, the telomer products are stable under experimental conditions, i.e. product formation is irreversible, but for more acidic substrates such as phenol, product formation is reversible and more 1,3,7-octatriene will be formed after the substrate has been depleted. 

The number of photoelimination reactions that occur in a concerted manner is very small. One of the best-characterized examples does not lead to the formation of a C—C bond between the two a-carbons. Rather, it involves the stereospecific photoelimination of CO from 3,5-cydoheptadienone 15 to 1,3,5-octatriene 16 (Scheme 2.5) [18]. The reaction occurs in a stereospecific manner with the relative stereochemistry of the two a-carbons determining the configuration of the resulting 1,5-double bonds. Another interesting and more relevant example involves the photodecarboxylation of enantiomerically pure aromatic esters derived from (+ )-or (—)-2-methylbutyric acid and 2,4,6-trimethylphenol 17, which occurs with 100% retention of configuration in the product 18. [19] While this is a promising lead that... 

C8H10O3S 2,4-xylenesulfonic acid 88-61-9 28.33 1 3275 2 14244 C8H12 trans,trans,trans-2,4,6-octatriene 15192-80-0 23.00 0.7961 1... 

CO2. propene. butenes, pentenes. pentadienes. hexene, hexadienes. hexatrienes. benzene, toluene, heptene. heplatriene. methacrylic acid, xylene, octatriene. octadiene. nonalriene. hexenedienoic add, decatriene. decatetraene. decapentaene. undecatriene. methylbenzoic acids, trimelhylbenzoic acid... 

The solvent properties of alcohols with short carbon chains are similar to those of water and such alcohols could be used as the nonaqueous catalyst phase when the products are apolar in nature. The first commercial biphasic process, the Shell Higher Olefin Process (SHOP) developed by Keim et al. [4], is nonaqueous and uses butanediol as the catalyst phase and a nickel catalyst modified with a diol-soluble phosphine, R2PCH2COOH. While ethylene is highly soluble in butanediol, the higher olefins phase-separate from the catalyst phase (cf. Section 2.3.1.3). The dimerization of butadiene to 1,3,7-octatriene was studied using triphenylphosphine-modified palladium catalyst in acetonitrile/hexafluoro-2-phe-nyl-2-propanol solvent mixtures [5]. The reaction of butadiene with phthalic acid to give octyl phthalate can be catalyzed by a nonaqueous catalyst formed in-situ from Pd(acac)2 (acac, acetylacetonate) and P(0CeH40CH3)3 in dimethyl sulfoxide (DMSO). In both systems the products are extracted from the catalyst phase by isooctane, which is separated from the final products by distillation [5]. 

The first report of a topochemical 1,6-polymerization of a conjugated triene was recently described by Lauher and co-workers [39]. In particular, the double ester of l,8-dihydroxy-2,4,6-octatriene and nicotinic acid (Scheme 2.3.5) was found to adopt a solid-state packing arrangement conducive for the 1,6-polymerization. Specifically, the molecules were oriented at a repeat distance of 7.2 A (Fig. 2.3.3(a)). Although the separation between terminal carbon atoms of adjacent triene moieties was somewhat large (4.09 A), the solid underwent a SCSC topochemical... 

Figure 2.3.3 Ball-and-stick representations of the crystal structure of the diester of 1,8-dihydroxy-2,4,6-octatriene and nicotinic acid (a) before reaction (b) after complete reaction.

C in aprotic solvents such as acetone or, more smoothly, in -PrOH, with 80% yield to 1,3,7-octatrienes (1). The presence of COj greatly enhances the catalytic activity of [Pd(PR3) ] (n = 2-4) and causes isomerization of 1 to 2,4,6-octatrienes. In formic acid, reductive dimerization proceeds and, depending on catalyst and cocatalyst, either... 

The cascade is initiated by a conrotatory 8w-electron ring closure of the polyene carboxylic acids 20, 21 to the isomeric cyclo-octatrienes 22 and 23, respectively, which subsequently undergo a disrotatory 6 r-elec-tron cyclization to 24 and 25, respectively. Termination of the cascade by an intramolecular Diels-Alder reaction yields either the tetracyclic endiandric acid 26a, b or the bridged derivative 27. 

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