1.3- Cycloheptadienes

The palladium-catalyzed cleavage of an allylic C-C bond forming cationic )t-allylpalladium intermediates is possible if the anionic counterpart is stabilized through charge delocalization on electron-deficient substituents [29]. Based on this concept, it has been shown that 3-vinylcyclopentenes undergo a two-carbon ring expansion to spirocyclic cyclopheptadienes in the presence of 

A chemo and stereoselective [4-1-2-i-l] access to cycloheptadienes fused to a five-membered ring, which involves the reaction of diazoalkanes with dienes tethered 

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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). 

The wM-diacetate 363 can be transformed into either enantiomer of the 4-substituted 2-cyclohexen-l-ol 364 via the enzymatic hydrolysis. By changing the relative reactivity of the allylic leaving groups (acetate and the more reactive carbonate), either enantiomer of 4-substituted cyclohexenyl acetate is accessible by choice. Then the enantioselective synthesis of (7 )- and (S)-5-substituted 1,3-cyclohexadienes 365 and 367 can be achieved. The Pd(II)-cat-alyzed acetoxylactonization of the diene acids affords the lactones 366 and 368 of different stereochemistry[310]. The tropane alkaloid skeletons 370 and 371 have been constructed based on this chemoselective Pd-catalyzed reactions of 6-benzyloxy-l,3-cycloheptadiene (369)[311]. 

The hydrochloride of the crude ester obtained above was added to 25 ml of 2 N hydrochloric acid. The whole was kept under reflux for 2 hours. The material dissolved and a new hydrochloride then reprecipitated. After cooling, the hydrochloride of the crude acid was filtered off, washed with iced water and then recrystallized from distilled water. 5.7 g of 7-[dibenzo(a,d)cycloheptadien-6-yl] aminoheptanoic acid hydrochloride were obtained, melting instantaneously at 226° to 230°C. 

A solution of dibenzo[a,e] cycloheptadiene in anhydrous xylene is added in a dropwise fashion with stirring to a suspension of sodium hydride in refluxing anhydrous xylene. 

Metrizoic acid Diazomethane Diazepam Epirizole Methoxsalen Pyrimethamine Dibenzo[a,el cycloheptadiene Butriptyline... 

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.)... 

In accordance with this, the reaction of the electron-donor-substituted butadienes 170 (R=Ph, OMe) with the arylcarbene complexes 163 yields divinylcyclopropane intermediates 168 with high chemoselectivity for the electron-rich double bond in 170, which readily undergo a [3,3]-sigmatropic rearrangement to give the as-6,7-disubstituted 1,4-cycloheptadiene derivatives... 

Scheme 37 Electronic effects of substituents on butadienes 170 determine the formation of cycloheptadienes 169 or cyclopentenes 172 [117,118]...

Scheme 8 Efficient formation of the conjugated cycloheptadiene core in tetracyclic compounds 42 during studies toward solanoeclepin A (39) [31]...

In the Supporting Information provided by Sinha et al., the formation of an unalike E/Z mixture of cycloheptadienes arising from 244d was presented... 

Wahrend Tropon durch Lithiumalanat zu 6-Oxo-cycloheptadien-(l,3) (58% d.Th.) reduziert wird, erhalt man aus Tropolon 4,5-Dioxo-cyclohepten (62% d.Th.)1H. 

Wahrend Tropon mit Lithiumalanat zu 6-Oxo-cycloheptadien-( 1,3) (s. oben) und Tro-polon zu 4,5-Dioxo-cyclohepten reduziert wird erhalt man aus a-Tropolon-methylather unter Ringkontraktion Benzaldehyd10 ... 

Compounds in which the RsSn group is attached to a 2,4-dienyl group, such as cyclopentadiene, cycloheptadiene, cycloheptatriene, and cyclononatetraene, whose formulas are shown, are fluxional. 

A derivative of cyclopentyne has been trapped in a matrix. Although cycloheptyne and cyclohexyne have not been isolated at room temperatures, Pt(0) complexes of these compounds have been prepared and are stable." The smallest cyclic allene" so far isolated is l-/err-butyl-l,2-cyclooctadiene 107." The parent 1,2-cyclooctadiene has not been isolated. It has been shown to exist transiently, but rapidly dimerizes." " The presence of the rert-butyl group apparently prevents this. The transient existence of 1,2-cycloheptadiene has also been shown," and both 1,2-cyclooctadiene and 1,2-cycloheptadiene have been isolated in platinum complexes." 1,2-Cyclohexadiene has been trapped at low temperatures, and its structure has been proved by spectral smdies." Cyclic allenes in general are less strained than their acetylenic isomers." The cyclic cumulene 1,2,3-cyclononatriene has also been synthesized and is reasonably stable in solution at room temperature in the absence of air." ... 

Ferrate 38 also turned out to catalyze [5 + 2]-cycloadditions. In this context, various vinylcyclopropane derivatives 52 were converted into the corresponding cycloheptadiene derivatives 53. The products were obtained in good to excellent diastereoselectivites favoring the 1,2-trans-disubstituted isomer 53a. 

Scheme 1.57 Test reaction with bis(thiazolines) ligands bridged by a dibenzo[a,c]-cycloheptadiene backbone.

When ring strain is relieved, Cope rearrangements can occur at much lower temperatures and with complete conversion to ring-opened products. A striking example is the conversion of ris-di vinyl cyclopropane to 1,4-cycloheptadiene, a reaction that occurs readily below -40° C.206... 

The preparation of N-carbethoxy-8-azabicyclo [5.1.0] oct-3-ene (158) from ethyl azidoformate (157) and 1,4-cycloheptadiene through a photolytic reaction, and its palladium(II)-catalyzed multistep rearrangement to N-carbethoxynortropidine (159), has been presented by Wiger and Retting as a new route to the 8-azabicyclo[3.2.1]octene skeleton (87) (Scheme 8). 

A number of zinc-bound bidentate bis(thioether) donor ligands were characterized as distorted tetrahedral complexes of zinc dichloride. The complexes 2,3-bis(methylthio)hexane,l,2-bis (methylthio) cyclohexane, and m-[5,6-bis(methylthio)-l,3-cycloheptadiene showed a variation in S—Zn—S angles.539... 

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. 

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