Cycloheptane, reaction

The model has been extended to cyclobutane hydrogenolysis and to cycloheptane reactions. Cyclobutane is assumed to undergo, like cyclopentane, planar adsorption on the surface (114). The stretching, however, is more pronounced than in the case of the C5 rings and propagates to all four C-C bonds of the molecule. These can then be broken easily, and that accounts for the absence of selectivity in the hydrogenolysis of alkylcy-clobutanes (114,115). 

Besides the Michael addition-initiated domino reactions presented here, a multitude of other anionic domino reactions exist. Many of these take advantage of an incipient SN-type reaction (for a discussion, see above). In addition to the presented SN/Michael transformations [97, 98, 100], a SN/retro-Dieckmann condensation was described by Rodriguez and coworkers, which can be used for the construction of substituted cycloheptanes as well as octanes [123]. Various twofold SN-type domino... 

Cycloheptane is about the largest ring in which the participation of the whole molecule can be expected in catalystic reactions. This molecule exhibits practically all the reactions described for cyclic hydrocarbons. The ring opening of methylcycloheptane is also selective, but total reactivity is much less than that of methylcyclopentane (702) ... 

Photolytic. The following rate constants were reported for the reaction of cycloheptane and OH radicals in the atmosphere 1.31 x 10 cmVmolecule-sec at 298 K (Atkinson, 1985) and 1.25 x 10 " cmVmolecule-sec (Atkinson, 1990). 

Tantalum hydride(s) also catalyzes the hydrogenolysis of cyclic alkanes (substituted or not) but the reachvity order decreases with the cycle size as cycloheptane > methylcyclohexane > cyclohexane > methylcyclopentane > cyclopentane for the latter no reaction is actually observed (Figure 3.8). Activity decreases with hme and becomes low after 20 h. 

All the cyclization reactions for the formation of cis cyclopentane-, cyclohexane-, and cycloheptane-fused and tram cyclohexane- and cycloheptane-fused derivatives are smooth. In contrast, the cyclizations of trans-2-hydroxy-l-cyclopentanecarboxamide failed. The difference in reactivity of cis and tram isomers is discussed in Section II,D. 

The nitrone 127 (96% ee) containing an additional carbon atom was synthesized in a similar manner as 124. However, for nitrone 127, no spontaneous cyclization took place (Scheme 12.43). Upon heating of 127 in toluene, an inseparable mixmre of product isomers was formed. It was also found that in the presence of a stoichiometric amount of ZnCl2, the reaction proceeded to give the bicyclo[4.2.1] product 128 as the only observed product with close to complete retention of enantiopurity (ee=94%). The authors propose a more polarized transition state of the Zn-mediated reaction with a well-developed positive charge on one of the carbon atoms of the alkene moiety to account for the inverted direction of the regioselectivity of the reaction (230). A subsequent reduction gave the functionalized cycloheptane 129. 

The photodecomposition of -alkanes at excitation energies slightly above the absorption onset involves both C-H and C-C bond decompositions [18]. The dominant process is the C-H scission, (H2) 0.8-0.9, and the contribution of C-C decomposition is small. In the photolysis of cyclohexane, cycloheptane, cyclooctane, and cyclodecane, however, only hydrogen evolution was observed [[Pg.375]

No reactions have been observed when methylenecyclopentane (182), methylenecyclohexane (183), or A1(7)-p-menthene (184) were submitted to photosensitized oxygenation.187 On the other hand, methylene-cycloheptane (185)1B7, jS-pinene (187)197, A4<10)-carene (190),202 and sabinene (193)205 undergo slow photosensitized oxygenation reactions giving rise to the formation of primary alcohols 186,189,191,192, and 194, respectively, after reduction of the primarily formed... 

The reaction of 1,2-dicarbonyl compounds with amidrazones, semicarbazide, thiosemicarbazide and aminoguanidine has also been used for the synthesis of condensed 1,2,4-triazines. Cyclohexane-, cycloheptane- and cyclooctane-1,2-diones (489) with amidrazones (453) afford the cycloalkatriazines (490) (78HC(33)189, p.66l). 

A review of intramolecular 4 + 3-cycloadditions of allyl cations has been presented.277 The 4 + 3-cycloaddition reaction of C(2)-substituted furans with 1,3-dimethyloxyallyl cations show high endo diastereoselectivity and a cis dia-stereospecificity.278 The tandem Peterson olefination/[4 + 3]-cycloaddition of tertiary alcohols (149) in the presence of filran and Lewis acids (TiCLt) furnishes cycloheptanes (150) in modest yields (Scheme 57).279 (Trimethylsilyl)methyl allylic sulfones (151) were used to investigate the scope and limitations of intramolecular 4 + 3-cycloadditions of allylic sulfones (Scheme 58).280 Lewis acid-catalysed 4 + 3-... 

Isopropyl esters of cyclohexanecarboxylic acids have been synthesized by using CBr4-2AlBr3 (1 atm CO pressure, —40°C).419 Isopropyl 1-methylcyclohexanecar-boxylate was isolated in the reaction of cycloheptane and methylcyclohexane (82% and 73% yield, respectively), whereas isopropyl 1-ethylcyclohexancarboxylate was formed from cyclooctane and ethylcyclohexane (67% and 69% yield, respectively). 

The following references contain additional examples of this method and corresponding reaction types Synthesis of 3-fluoroethyl-2-cyclopenten-l-ones [35], preparation of functionalized bicyclo[5.3.0]decane systems and conversion of 1,2-divinylcyclopropanes to functionalized cycloheptanes [36] e.g. karaha-naenone [37], ( )-/Thimachalene [38][39]. Metal-catalyzed ring expansions in which cyclopropane (e.g. [40] [41] [42] [43] [44]) or aziridines (e.g. [45] [46]) and diaziridines (e.g. [45]) function as essential moieties are well known reactions. 

The results for cycloheptane after 30 min reaction time are shown in Table 17.6. Methylcyclohexane is the major product, with a selectivity of 97%, in addition to small amounts of four dimethylcyclopentanes and ethylcyclopentane. The reaction of methylcyclohexane under the same conditions also produced the latter five compounds, and the system reached its equilibrium state after 90min of reaction. 

The reaction results of cycloheptane and cyclooctane indicate that the monomolecular pathway is followed, preserving the cyclic structure, without the formation... 

Table 17.6 Product distribution for the reaction of cycloheptane at 50°C after 30min reaction time over S04/Zr02.

Section 1.13.5 Miscellaneous reactions. Takeshita and coworkers reported the remarkable use of intramolecular ene reactions to form cycloheptanes and cyclooctanes. Pyrolysis of (216) in toluene at 200 C gives 97% of the cycloheptane (215). Reaction of (216) with SnCU in THF gives 85% of cyclooctane (217), which is an intermediate in the synthesis of cycloaraneosene. 

From another viewpoint, the value of the arene-alkene meta cycloaddition arises from its capacity to produce a cycloadduct (66 equation 14) with three new rings and up to six new stereocenters, an impressive feat even when compared with the highly regarded Diels-Alder cycloaddition. Moreover, the cycloadduct can be used in the synthesis of a variety of commonly encountei structural types including cyclopentanes, cycloheptanes, bicyclo[3.2.1]octanes and bicyclo[3.3.0]octanes. While fr uently overlooked in some discussions of reaction classification, the overall processes leading to cycloheptanes, bi-cyclo[3.2.1]octanes and bicyclo[3.3.0]octanes are clearly classifiable as [5C + 2C], [3C + 2C] and [3C + 2C] cycloadditions, respectively. Examples of these types will be given in the following section. 

Cycloheptanes.—Two full papers have appeared on subjects mentioned in Vol. 1 Demole and Enggist s karahanaenone synthesis,and the irradiation of eucarvone. " Another paper concerning the irradiation of eucarvone has appeared in this case the substrate was protonated by carrying out the reaction in fluorosulphonic acid at — 78 °C. The products obtained after quenching the reaction with potassium carbonate in methanol are shown in Scheme 5, together... 

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