1,3-Cycloheptadien

Diacetoxylation of various conjugated dienes including cyclic dienes has been extensively studied. 1,3-Cyclohexadiene was converted into a mixture of isomeric l,4-diacetoxy-2-cyclohexenes of unknown stereochemistry[303]. The stereoselective Pd-catalyzed 1,4-diacetoxylation of dienes is carried out in AcOH in the presence of LiOAc and /or LiCI and beiizoquinone[304.305]. In the presence of acetate ion and in the absence of chloride ion, /rau.v-diacetox-ylation occurs, whereas addition of a catalytic amount of LiCl changes the stereochemistry to cis addition. The coordination of a chloride ion to Pd makes the cis migration of the acetate from Pd impossible. From 1,3-cyclohexadiene, trans- and ci j-l,4-diacetoxy-2-cyclohexenes (346 and 347) can be prepared stereoselectively. For the 6-substituted 1,3-cycloheptadiene 348, a high diaster-eoselectivity is observed. The stereoselective cij-diacetoxylation of 5-carbo-methoxy-1,3-cyclohexadiene (349) has been applied to the synthesis of dl-shikimic acid (350). 

Cyclopentadiene is very reactive in Diels-Alder cycloaddition reactions, but 1,3-cyclohexadiene is less reactive and 1,3-cycloheptadiene is nearly inert. Explain. (Molecular models are helpful.)... 

The parent system 20 was prepared from the 1,3-cycloheptadiene endoperoxide (Eq. 15) in 38% yield M,32). However, this double bond is quite sluggish towards saturation with diimide, so that a large excess of the diimide reagent is necessary, preferably recycling the incompletely reduced reaction mixture several times. 

The cycloaddition behavior of 2 in the presence of 1,3-cycloheptadiene [4] is comparable to that just described above for cyclohexadiene. Treatment of the Si-dichloro substituted [2+2] adducts 14 with phenyl Grignard reagent leads to the crystalline derivative -14a. 

As was seen for 1,3-cyclohexadiene, the data in Pedley and Roth report conflicting measurements for the enthalpy of formation of 1,3-cycloheptadiene, 51. The values differ by some 3 kJ mol-1. This is often a non-negligible difference, but either result is plausible the disproportionation reaction 26... 

The 1,4-oxidation has also been extended to the use of alcohols as nucleophiles45. By performing the reaction in an alcohol as the solvent with Pd(OAc)2 as catalyst and p-benzoquinone as the oxidant, a 1,4-dialkoxylation was obtained (equation 17). It was essential to add a catalytic amount of acid to get a reaction. The reaction is highly regio-and stereoselective and 1,3-cyclohexadiene and 1,3-cycloheptadiene afforded exclusively 1,4-yyw addition products (Table 1). 

However, the reaction of 1,3-cycloheptadiene is less regioselective. Isoprene and E,E-2,4-hexadiene afford 1,2-/1,4-adducts in ratios of 87 13 and 83 17, respectively. The high selectivity for 1,2-addition (>95%) to 1,3-pentadiene is opposite to the corresponding oxymercuration of the same diene, which has been reported159 to give mainly 1,4-adducts. The different regiochemistry has therefore been explained by assuming that sulfomercu-ration occurs under kinetic control whereas oxymercuration occurs under thermodynamic control. 

Cyclopentadienes, 1,3-cyclohexadienes, 1,3-cycloheptadienes, as well as furan and aklyl-substituted furans, have been investigated as substrates of photosensitized oxygenation reactions, while aromatic compounds such as anthracenes and tetracenes as well as aryl-substituted carbo-and heterocyclic pentadienes were studied in direct and indirect (photosensitized) photooxygenation reactions. 

This compound is prepared as described in Section 13.B, but substituting 1,3-cycloheptadiene (Aldrich). Yield 80%. 

A combinatorial approach was applied to evaluate various catalysts for the animation of 1,3-dienes.594 Complexes formed from [(T 3-C3H5)PdCl]2 and PPh3 were the most active to induce the reaction of a broad range of primary and secondary ary-laminesand 1,3-cyclohexadiene, 1,3-cycloheptadiene, or 2,3-dimetyl-1,3-butadiene to give allylamines. The enantioselective version of the transformation is also very effective ... 

In contrast, 1,3-cycloheptadiene and 1,3-cyclooctadiene whose double bonds are twisted out of coplanarity are considerably less reactive and give endoperoxides in lower yields.420... 

Photocyclization of 1,3-cycloheptadienes is a particularly efficient process, since ring fission is not possible. The photocyclization of 1,3-cycloheptadienes in conjunction with a recently developed synthesis of substituted 1,3-cycloheptadienes (159) constitutes an important synthetic entry to the bicyclo[3.2.0]heptane series. Irradiation of 1,3-cycloheptadiene (Formula 361) gives the bicyclic photoisomer (Formula... 

Formula 375 (165). Substituents seem to exert relatively little effect on the photoisomerization of 1,3-cycloheptadiene. Thus irradiation of 1,4-diphenyl-l,3-cycloheptadiene (166), 5-methoxy-2.4-cycloheptadienol (161,162), 2,4-cycloheptadienol (161,162), 5-methoxy-2,4-cyclohepta-dienone (161,162), and eucarvone (60) gives in each case the bicyclic photoisomer. Eucarvone gives other products as well (see Sec. II,C). The only exceptions to the generality of the photoisomerization of 1,3-cycloheptadienes encountered so far is the irradiation of 3,5-cyclohepta-dienone (Formula 376) (R = H) and 2-methyl-3,5-cycloheptadienone (Formula 376) (R = Me) which give 1,3,5-hexatriene (Formula 377)... 

Seven-membered rings. Relatively few seven-membered rings have been studied in the free state. 1,3-cycloheptadiene (79)357 is planar except for C6 which is bent... 

Very stable diene complexes can be prepared by the reaction of conjugated dienes with Fe(CO)5, Fe2(CO)9 or Fe3(CO)12 by heating or under irradiation. For synthetic purposes, the complexes of acyclic 1,3-dienes, 1,3-cyclohexadienes and 1,3-cycloheptadienes are useful. 

Cyclohexadiene yielded only the two (Z)-cross-ozonides with the upper one predominating. 1,3-Cycloheptadiene afforded the two (Z)-cross-ozonides with the lower one predominating, and 1,3-cyclooctadiene gave only the lower (Z)-cross-ozonide. At room temperature in CH2CI2, the CM-double bonds isomerize to /ram-configurations. 

P(CH3)3, P(OCH3)3], For each of the [Cr(CO)3(j/4 CH-diene)] complexes 39g, 37n, and 37o two enantiomers are expected. As a consequence of the C—H—Cr bridge from C-5 or C-6 of the 1,3-cyclohexadiene, and from C-5 or C-7 of the 1,3-cycloheptadiene, both ligands lose their inherent mirror planes. The situation is somewhat different with the 2,4-dimethyl-1,3-pentadiene complex (37n). Here only the 4Z methyl group is able to form the C—H—Cr bridge. Due to the two coordination modes of the diene, R or S, a pair of enantiomers is present for 37n. Finally, 37r forms two diastereomeric pairs of enantiomers, because the C—H—Cr bridge can be formed from C-5 or C-6 and the diene can be coordinated in the R or S mode. 

In 38o, the ri4 CH-1,3-cycloheptadiene group adopts the R configuration, and the trimethylphosphine ligand is found at the d position. In 39n, the trimethylphosphite ligand occupies the d site also, but the 4-dimethyl-... 

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