1,4-Diphenylbutadiene

The oxidative coupling of alkenes which have two substituents at the 2 posi-tion, such as isobutylene, styrene, 2-phenylpropene, 1,1-diphenylethylene, and methyl methacrylate, takes place to give the 1,1,4.4-tetrasubstituted butadienes 285 by the action of Pd(OAc)2 or PdCF in the presence of sodium acetate[255-257]. Oxidation of styrene with Pd(OAc)2 produces 1.4-diphenylbutadiene (285, R = H) as a main product and a- and /3-acetoxystyrenes as minor pro-ducts[258]. Prolonged oxidation of the primary coupling product 285 (R = Me) of 2-phenylpropene with an excess of Pd(OAc)2 leads slowly to p-... 

Diphenylbutadiene has been obtained from phenylacetic acid and cinnamaldehyde with lead oxide, by the dehydrogenation of l,4-diphenyl-2-butene with butyllithium, and by the coupling reaction of benzenediazonium chloride and cinnamyl-ideneacetic acid." The present method gives better yields than those previously reported, is adaptable to the preparation of a variety of substituted bistyryls, and is relatively easy to carry out. 

Diphenylbutadiene (16, 28) In yields of 50 per cent by reduction of 0-bro-mostyrene with hydrazine hydrate in the presence of a palladium catalyst and alco-... 

The reaction is also sensitive to steric effects thus of the three iso-merides of 1,4-diphenylbutadiene (88a — 88c), only the trans-trans form (88a) will undergo a Diels-Alder reaction ... 

Towards the end of this section it may be worthwhile to point out some new reactions with high-valent metals and TBHP. The first is a pyridinium dichromate PDC-TBHP system134. Nonsubstituted or alkyl-substituted conjugated dienes, such as 1,3-cyclooctadiene (87) and others (also linear dienes), yield keto allyl peroxides 88 (equation 18), whereas phenyl-substituted dienes such as 1,4-diphenylbutadiene (89) gave diketo compounds, 90 (equation 19). In further research into a GIF-type system135 with iron and TBHP, limonene gave a mixture of products with carvone as the major product. The mechanism is thought to proceed initially by formation of a Fe(V)-carbon... 

That Grignard reagents are widely used for the preparation of various types of organotin compounds is further illustrated by l-trimethylstannyl-2-phenylethene, isolated120 in 63% yield, besides 1,4-diphenylbutadiene (28%) as a side-product. 

Styrene and indene derivatives (Scheme 2, Y = Ph) are dimerized to l,4-dimethoxy-l,4-diphenylbutanes or 1,4-diphenylbutadienes (Table 7, numbers 1 and 2) [52]. The product distribution is in some cases strongly dependent on the anode potential and the supporting electrolyte. Dimerization is promoted by a-substituents that stabilize the intermediate radical cation, for example, phenyl, vinyl, alkoxy, dialkylamino groups. IJ-Alkyl substituents strongly decrease the yield of dimers and favor formation of dimethoxy-lated monomers. 

Low-lying vacant orbitals of alkali metal cations can, consequently, accept an unpaired electron density even if it is delocalized over an extended n system of carbon chains. The anion-radical of 1,4-diphenylbutadiene can exist in i-trans and in -cis forms. The relative amounts of these geometrical isomers appear to depend highly on the counterion/solvent system. Li and K+ were studied as counterions THF, 2-MeTHF, and DME were employed as solvents (Schenk et al. 1991). Interaction between the anion-radical and the cation contributes to a stabilization of... 

However, too few examples are available to allow a general prediction of the position for hydrogen attachment. Electrochemical reduction of 1,4-diphenylbutadiene gives products from both 1,2- and 1,4-attachment of hydrogen [6], The 1,2-addition product predominates in absence of a good proton donor because electro-chemically generated base catalyses isomerisation of the 1,4-addition product. Reduction of a steroid diene 4 gives the 1,4-addition product [17],... 

Within the general description of ligand exchange, the relative stability of a variety of magnesium-olefin complexes/magnesacycles has been studied. For example, 1,4-diphenylbutadiene replaces the parent butadiene in equation 20 to form the penta-coordinated magnesium compound. ... 

In practice the low potentials permit a choice of approaches this is illustrated in Scheme 18 for a Wittig reaction in the presence of EGB wherein the desired product, 1,4-diphenylbutadiene, may be formed either from a reactive aldehyde (cinnamaldehyde) and an ylid from a benzylic phosphonium salt, or from a less reactive aldehyde and the ylid from a more acidic phosphonium salt The stereochemical course of the Wittig reaction is particularly sensitive to reaction conditions, especially cations which may be present. This point is partly made in Scheme 18 but deserves further elaboration. 

Dihydrobenzo[c]furans have been dehydrogenated directly to benzo[c]furans using / -chloranil in xylene.lo .ioe stereochemistry of the 4,5-diaroylcyclohexenes is generally not known. Sometimes two isomers have been isolated. As was reported by Adams and Geissman, the reaction of 2,4-hexadiene with dibenzoylethylene gave a major product in 66% yield (mp 136—137°C) in addition, an isomeric compound (mp 86-88 C, 5%) was isolated. Two isomeric adducts (mp 120°C, 178-179°C) have also been obtained from the reaction of 1,4-diphenylbutadiene with dibenzoylethylene. Both cis- and tra 5-dibenzoylethylene with 2,3-dimethylbutadiene gave the same stereoisomer. ... 

The Diels Alder reaction of the acyclic diene and 146 may result in unexpected products, however. As reported by Ried, the reaction of 1,4-diphenylbutadiene and 146 may, under drastic conditions, give the aromatized compound (148) and l,3,4,7-tetraphenylbenzo[c]furan (149) in varying amounts, depending on the conditions. In methylglycol/propanol (6 hr reflux) a substance was isolated (mp 147-148°C, 59%) which has tentatively been formulated as 150. One final goal of the sequence described seems to be unaffected by these anomalous reactions, however Diels-Alder adducts of benzo[c]furans can be obtained in a one-step reaction from a diene, 146, and an appropriate olefinic compound in acetic acid/acetic anhydride as shown in Eq. (7). ° ... 

Irradiation of 138 (Z > 370 nm) together with 1,3-cyclohexadiene, 1,4-diphenylbutadiene, l-carbomethoxy-4-phenylbutadiene and co-nitro-... 

Diaroylcyclohexadienes, which can be prepared from acyclic dienes and dibenzoylacetylene, undergo ring closure with p-toluenesulfonic acid in benzene to afford benzo[c]furans (Scheme 67) (71JOC1048). 1,4-Diphenylbutadiene and dibenzoylacetylene undergo Diels-Alder reaction to give the o-diaroylbenzene (237) and 1,3,4,7-tetraphenyl-benzo[c]furan (238) the ratio of each product obtained depends on the reaction conditions. 

The reaction of Grignard reagents with thiophene and benzo[6]thiophene in presence of bis(triphenylphosphine)nickel dichloride catalyst results in ring opening with replacement of C—S bonds by C—C bonds (Scheme 38) (79CC637). Thus phenylmagnesium bromide gives 1,4-diphenylbutadiene and phenylstilbene respectively as a 1 1 mixture of stereoisomers. 

The presence of 7T—7T or n—71 conjugated systems does not ensure absorption of visible light or generation of color. However, all colored oiganic compounds, including pigments, possess extended conjugated resonance systems. Thus, whereas 1,4-diphenylbutadiene is colodess, 1,6-diphenylhexatriene is colored. 

The reagent is unstable and so is generated in the presence of the carbonyl compound by dehydrohalogenation of the alkyltriphenylphos-phonium bromide with phenyllilhium in dry ether in a nitrogen atmosphere. There are various modifications, such as the phosphonate. in which djethylbenzylphosphonate, cinnamaldehyde, and sodium methoxide yield 1,4-diphenylbutadiene. 

There are a few reports in the literature in which the carbonyl group has been formally replaced by another unsaturated function. Thio-benzophenone (268) undergoes photochemical 1,2-cycloaddition to a-phellandrene (269) to give the thietane (270), together with the sulfur heterocycles (271 and 272) formed by 1,4-cycloaddition.298 Isoprene, cyclopentadiene, and 1,4-diphenylbutadiene also undergo 1,4-cycloaddition with thiobenzophenone, but 1,3-cyclooctadiene... 

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