1.4- Cydohexadiene

Aryl- or alkenylpalladium comple.xcs can be generated in situ by the trans-metallation of the aryl- or alkenylmercury compounds 386 or 389 with Pd(Il) (see Section 6). These species react with 1,3-cydohexadiene via the formation of the TT-allylpalladium intermediate 387, which is attacked intramolecularlv by the amide or carboxylate group, and the 1,2-difunctionalization takes place to give 388 and 390[322]. Similarly, the ort/trt-thallation of benzoic acid followed by transmetallation with Pd(II) forms the arylpalladium complex, which reacts with butadiene to afford the isocoumarin 391, achieving the 1,2-difunctionalization of butadiene[323]. 

FIGURE 11 2 Heats of hy drogenation of cydohexene 1 3 cydohexadiene a hypo thetical 1 3 5 cydohexa triene and benzene All heats of hydrogenation are in kilojoules per mole... 

The positional selectivity of the cycloadditions of 351 is of particular interest, since the [2 + 2]-cydoadditions proceed exclusively at the double bond bearing the oxygen atom, whereas the [4 + 2]-cycloadditions occur at the double bond remote of the oxygen atom with the exception of the major product resulting from 1,3-cydohexadiene (369, Scheme 6.75). Supposing diradical mechanisms, these findings require that... 

Cydohexadiene detonated, in samples less than 5cc, under the influence of a wave produced by the expln of 1.1 g Tetryl. The expln has an induction period of 5 sec after the critical pressure of 1500 atm/min is reached. It... 

Fig. 8. Pressure dependence of the endo-exo radio (In relative endo-exo ratio) in the determination of 1,3-cydohexadiene (17 a), sensitized by 1,4-dicyanonaphthalene (21) in aceto-nitrille and benzene [64]...

Racemic tandem additions Mild carbon nucleophiles add to the [Os]-anisolium complex 27 exclusively at C3 to afford substituted 1,3-cydohexadiene complexes 29-32 in moderate to high yields (Table 8) [21]. Nucleophiles that have been utilized in this manner include MMTP (29 and 30), N-methylpyrrole (31), and 2-trimethylsilyloxyfuran (32). As with other tandem additions to [Os] complexes, both the nucleophile and the electrophile add to the arene face opposite to that involved in metal coordination, such that the products are those of syn addition. 

Cyclopropan-[Pg.1030]

Interestingly, sequential migration-Diels-Alder reactions of tert-butyldioxy die-none 77 in the presence of 1,3-cydohexadiene gave as-fused octahydroanthraqui-none 78 stereoselectively (78%) (Eq. 3.86). 

Products. Photolysis of 1,3-cyclohexadiene gives rise to 1,3,5-hexatriene of unknown stereochemistry. During irradiation in the condensed phase initial product is the m-triene which subsequently isomerizes photochemically. The other primary processes which seem to originate directly in 1,3-cydohexadiene are dehydrogenation ... 

THBA from butadiene 2,5-c Wtf-methylene from 1,3-cydopentadiene 4-methyl- PH B A from 2-methylbutadiene 2,5-tW< -etliylene from 1,3-cydohexadiene. 

Stereochemistry the Boron Trifluoride-Catidyzed Cydoaddition of MonO C-Snbstituted A-Acylimines with 1,3-Cydohexadiene... 

Electrocycllc interconversions of 2,4,6-octatrlene isomers and 5,6-dimethyl-1.3-cydohexadiene Isomers. 

Give the structure of the Diels-Alder adduct of 1,3-cydohexadiene and dimethyl... 

Diene A is similar m structure to 1,3-cydohexadiene. which reacts well in Diels-Alder cycloadditions O ablc 14- IX In diene B, however, the ends of the diene are locked in a zigzag conformation (called "s-traas") that puts the end carbons too far apart to bond to the two alkene carbons of a dienophile. Figure 14-9 illustrates how the Diels-Alder reaction involves a diene in a U-shaped conformation (called s-cis ), which puts its end carbons close together. Dienes (like B) that cannot achieve this conformation will not participate with dienophiles in Diels-Adler reactions. 

Scheme 17 A plausible catalytic mechanism for the hydrogen-mediated coupling of 1,3-cydohexadiene to a-ketoaldehydes as corroborated by deuterium labeling...

The magnetic dipole approach used earlier gives a ring current contribution calculated as 1.46 ppm. Local contributions can be estimated from the chemical shift of the protons of a nonaromatic reference such as 1,3-cydohexadiene, which resonates at 5.8 ppm (protons in 2- and 3-position). With 5.8 +1.46 = 7.26 ppm, the calculated shift is quite close to the experimental value of 7.3 ppm. Waugh and Fessenden [42] and Johnson and Bovey [43] improved the dipole model by assuming a pair of current loops above and underneath the benzene ring separated by a distance of 0.9 or 1.28 A (Figure 13.5). 

I -bromo-2-hexene. 1532. (a) The product isoiiieiized, 1630 suggests conjugated (b) 2-propyl-1.3-cydohexadiene. 

Dehyd rohalogenation of 1,2-dihalides (with the elimination of two molar equivalents of HX) normally leads to an alkyne rather than to a conjugated diene. However, when 1,2-dibromocyclohexane is dehydrohalogenated, 1,3-cydohexadiene is produced and not cyclohexyne. What factor accounts for this ... 

Hydrosilylation of cyclic dienes also worked well to give aUylic silanes. Thus, palladium-catalyzed hydrosilylation of 1,3-cyclopentadiene and 1,3-cydohexadiene afforded the corresponding allylsilanes in good yields [13,14]. 

The reaction was also performed in acetone in the presence of 5-10 equiv. of a carboxylic acid [58]. In this way, sohd carboxylic acids can be used. A number of different dicarboxylates were prepared in this manner from acetic acid, trifluoroacetic acid, pivahc acid, and benzoic acid. An example where the cis- and trans-1,4-dibenzoates from 1,3-cydohexadiene were obtained stereoselectively is shown in Scheme 11.12. 

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