Cycloheptatriene hydrogenation

In contrast to the resistance of cycloheptatriene systems (e.g., tropolone) towards hydrogenation, 3-benzothiepin 3,3-dioxide is readily hydrogenated at atmospheric pressure in the presence of Raney nickel to give l,2,4,5-tetrahydro-3-benzothiepin 3,3-dioxide in 78% yield.82... 

A suspension of 100 g (0 48 mole, 33% excess) of phosphorus pentachloride in 800 ml of carbon tetrachloride is prepared in a 1-1 flask equipped with an efficient stirrer and an exit valve for the hydrogen chloride that is evolved ( ote 1) Tropilidene (cycloheptatriene, 24.2 g of 91% mateiial, 0.24 mole) (Note 2)... 

For instance, cycloheptatriene has been selectively hydrogenated at 1 bar H2 pressure at 20 °C, yielding cycloheptene. The selectivity depended largely on the solvent used, ranging from 100% when n-hexane was used, or 99.5% in THF, to very low values when ethanol was employed. The conversion is quantitative in THF and ethanol, but in n-hexane it did not exceed 65% consequently, the authors concluded that THF gives the best combination of selectivity and conversion. In this case, the formation of cycloheptane was observed only after the substrate cycloheptatriene had completely been consumed. 

It was shown that [1,5]-hydrogen shift occurs in this case about 30 times more quickly than that in the cycloheptatriene, while the butadienylcyclopropane rearrangement proceeds 3 x 10 9 slower than the Cope rearrangement of the isomeric 2,5-diene 11054. 

For cycloheptatriene and a series of its derivatives various thermal unimolecular processes, namely conformational ring inversions, valence tautomerism, [1,5]-hydrogen and [l,5]-carbon shifts, are known. An example of such multiple transformations was described65 which can provide a facile approach to new polycyclic structures by a one-step effective synthesis (yields up to 83%) of the two unique ketones 156 and 157. The thermolysis of the neat ether 151 at 200 °C for 24 h gives initially the isomeric allyl vinyl... 

Cyclohexa-1,3-diene is readily hydrogenated to cyclohexene, but cycloheptatriene is hydrogenated more slowly to give a mixture of cycloheptene and cyclohepta-1,3-and 1,4-diene. Further hydrogenation of the conjugated diene is extremely slow. Cyclohepta-1,4-diene and cyclo-octatetraene are not hydrogenated. 

The molecular ions of toluene and cycloheptatriene are capable of mutual isomerization prior to dissociation. [49,53,56] It has been known for long that hydrogen loss from toluene molecular ions takes place as if all eight positions within these ions were equivalent, and this has been interpreted in terms of complete hydrogen scrambling prior to dissociation. [57] The extent of isomerization becomes apparent from the close similarity of the toluene and cycloheptatriene El mass spectra... 

Reaction of CF with benzene generates the 7-fluoronorcaradien-7-ly radical (39), which abstracts hydrogen (from added isobutane) and opens to 7-fluorocyclohepta-triene (40). Cycloheptatriene (10) is trapped as tropylium fluoroborate (41) by the addition of BF3 (Eq. 21)P An additional product of CF + benzene is fluorobenzene (42), in which labeling studies demonstrate that the attacking carbon contains the fluorine in 42. The interesting transfer of CH in Eq. 28 is proposed to account for the formation of 42. " ... 

The reactions of cycloheptatriene with transition metal atoms are similar to those of cyclopentadiene. In both cases, the reactions can involve extensive migration of hydrogen in the formation of the final product (9, 10, 133, 136) ... 

Thermal 1,5 hydrogen shift of cyclopentadiene and 1,3,5-cycloheptatriene, and methyl shifts in the corresponding methyl-substituted derivatives and in methyl-1,3-... 

Hydrocarbons with easily abstractable hydride ion such as 1,4-cyclohexa-diene,227 cycloheptatriene,223 or compounds possessing tertiary or benzylic hydro-gen217,218,223 230 231 are suitable substitutes for silanes. In fact, this was the case in the first ionic hydrogenation observed by Ipatieff and coworkers. In an attempt to carry out alkylation of p-cymene with 3-methylcyclohexene, hydrogenation of the latter occurred, where p-cymene was the hydride ion source ... 

The most prevalent base-catalyzed reaction of an endoperoxide is the Kornblum-DeLaMare decomposition [97a] which leads to a hydroxy ketone by removal of a proton from the carbon adjacent to the peroxy linkage [9b,90b,97], The formation, in a basic solvent as acetone, of hydroxyfuranones 69 (Sch. 38) in the photo-oxygenation of a,a -unsubstituted furans might occur via a similar rearrangement [60e]. Attempts to induce asymmetry in endoperoxides with enantiotopic hydrogens or with chiral bases have led to moderate success [98]. The Et3N-catalyzed rearrangement of substituted cycloheptatriene endoperoxides 92 leads to... 

Reaction with cyclopentadienones or their acetals also occurs readily hydrolysis of the acetals and decarbonylation also leads to cycloheptatrienes, while hydrogenation prior to the elimination produces cyclohepta-1,4-dienes 221 222) ... 

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