Cycloheptane derivatives

As ring size increases, there are progressively more conformations that need to be considered. For cycloheptane, four conformations have been calculated to be particularly stable. NMR investigations indicate that the twist-chair is the most stable. Various cycloheptane derivatives adopt mainly twist-chair conformations. ... 

The difference in stability between the cychc six- and seven-membered methoxy tel-luroxides is noteworthy. Indeed, while the cyclohexane derivative is stable and isolable, giving ring contraction on treatment with 1 equiv of MCPBA, the cycloheptane derivative is unstable, suffering telluroxide elimination (like cycloheptene formation from cyclohep-tyl phenyl telluride), as will be shown in Section 4.7. 

The enthalpy of fomation of two such species has been measured, namely the cyclopropane and cycloheptane derivatives. The difference between the values for these two species, both as solids, is 238.1 kJmol . Is this difference plausible Consider the difference between the enthalpies of formation of the parent cycloalkanes as solids, 194 kJ mol . The ca 44 kJ mol discrepancy between these two differences seems rather large. However, there are idiosyncracies associated with the enthalpies of formation of compounds with three-membered rings and almost nothing is known at all about the thermochemistry of compounds with seven-membered rings. Rather, we merely note that a seemingly well-defined synthesis of cycloheptyl methyl ketone was shown later to result in a mixture of methyl methylcyclohexyl ketones, and superelectrophilic carbonylation of cycloheptane resulted in the same products as methylcyclohexane, namely esters of 1-methylcyclohexanecarboxylic acid. The difference between the enthalpies of formation of the unsubstituted alicyclic hydrocarbons cycloheptane and methylcyclohexane as solids is 33 kJmol . This alternative structural assignment hereby corrects for most of the above 44 kJ mol discrepancy in the enthalpies of formation of the two oximes. More thermochemical measurements are needed, of oximes and cycloheptanes alike. 

Cyclopentadiene Diels-Alder adducLs such as 11 are highly strained. Huw M.L. Davies of the State University of New York, Buffalo, has established (J. Am. Chem. Soc. 2004,126,2692) an important strategic connection between Diels-Alder adducts such as 13 and the enantiomerically-enriched cycloheptane derivative 14. Oxidative cleavage of the alkene of 14 would lead to a cyclohexane derivative that would be difficult to access by other means. The same adduct 14 (albeit in racemic form) is also available directly by AIC1,-mediated addition of mcthacrolein 15 to cyclopentadiene. 

A particular subset of these ligated dialkyls are those in which the ligand is tethered to the cyclopentadienyl ligand. Thus, chromacyclopentane and cycloheptane derivatives stabilized by the (7/ 7/ -Me4C5CH2CH2NMe2) ligand have been prepared and their reactivity supports the intermediacy of such metallacycles in the catalytic trimerization of ethylene. A variety of donor-ligand-substituted cyclopen-tadienylchromium(III) complexes with amino and phosphino substituents has been prepared and screened for an ethylene polymerization activity. ... 

Cycloheptane derivatives (7, 192-193). Wender et a/. have applied their cycloheptane annelation procedure to total syntheses of the pseudoguaianolides damsinic acid (1) and confertin (2). The paper describes the synthesis of 1-lithio-l-methyl-2-vinylcyclopropane, which is the annelation reagent utilized in the pseudo-guaianolide syntheses. 

No details were given so far about the structure of these compounds. One of the most interesting applications of the method could be the synthesis of enantiomerically pure, highly functionalized cycloheptane derivatives, since divinylcyclopropanes should be obtainable by the appropriate rearrangement of other primary products. 

Cycloheptane derivatives. Annelated cycJohepfane derivatives have been prepared by reaction of (1) with 3-alkoxyenoncs to form 1,2-divinylcyclopropanes (2), which rearrange thermally to annelated cycloheptadiene derivatives (3) (equation I). Actually, either trans- or rts-(l) or a mixture of the two can be used since both cis- or trans- 2 rearrange on thermolysis to the same product (3), although trans-(2) requires somewhat more drastic conditions. The overall yield of (3) using a 7 3 mixture of cis- and trans-i ) is 2 7o ... 

Recently, Cdrdova and co-workers revealed a regiospecific, highly chemo-, diastereo-, and enantioselective one-pot organocatalytic domino reaction of a, 3-unsaturated aldehydes 269, aromatic aldehydes 106, and phenylhydroxyamine 265, providing cycloheptane derivatives 270, Scheme 3.86 [109]. The tandemmulti-component [2+3]/[3 + 2] cycloaddition afforded six new bonds and five new... 

Several cycloheptane derivatives have been prepared using intramolecular Friedel-Crafts reactions including the tetracyclic ketone (26) and double dibenzotropones , e.g. Acid-catalysed cyclizations of (o-(l-indanyl)-carboxylic acids (28 n = 3... 

Thermal homo [1,5] hydrogen shifts have been used as a ring-expansion route to cycloheptane derivatives e.g. heating the bicyclic ketone (89) at 200°C for 2h caused isomerization to the cycloheptyl ketone (90). This route was used to prepare a functionalized hydroazulene. ° ... 

Bicyclo[3,2,0]heptan-6-ones and bicyclo[3,2,0]hept-2-en-7-ones are cleanly iso-merized to cyclohept-2-enones and cyclohepta-2,4-dienones, respectively, in strong acids such as FSO3H and 96% H2SO4, e.g. (174) -> (175), and a useful method of converting phenols into cycloheptane derivatives of type (176) is by flash vacuum pyrolysis of their propiolate esters. Mixtures of isomeric cycloheptadienols are produced when the epoxide resulting from addition of dimethylsulphonium methyl-ide to acylvinyIcyclopropane is heated at 180 °C for 12 h. ... 

The Influence of Dienophile Structure on Reactivity and Stereoselectivity in Tandem Cycloadditions of 1,3,4-0xadiazoles The best dienophiles for the tandem cycloadditions of 1,3,4-oxadiazoles are electron-rich, unhindered, and strained alkenes. These components are used in excess because they also serve as the dipolarophiles in the next step. The yields are often moderate, probably, due to the harsh reaction conditions. Thus, cyclopentene reacts with oxadiazole 440 (Scheme 16.88) to provide the oxabi-cycloheptane derivative 443 in 33% yield [167a]. The product configuration has been established as synlanti with respect to the oxygen atom bridge. It is not clear which of the two steps ([4 + 2] or [3 - - 2]) produced which relationship. Ethylene has also been used as the dienophile in the earliest report. 

Zhao, G.-L, and Cordova, A. (2007) Tetrahedron Lett., 48, 5701-5705. The same catalytic machinery later served to engineer a more complex MCR leading to chiral cycloheptane derivatives, see ... 

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