1.3.5- Cycloheptatrien compounds

SAMPLE SOLUTION (a) Cycloheptatriene (compound A) is not aromatic because, although it does contain six it electrons, its conjugated system of three double bonds does not close on itself—it lacks cyclic conjugation. The CH2 group prevents cyclic delocalization of the tt electrons. ... 

Complexes containing CHT may be obtained by reactions of cycloheptatriene compounds with triphenylmethyl tetrafluoroborate ... 

If triphenylmethyl chloride in ether is treated with sodium, a yellow colour is produced due to the presence of the anionic spiecies PhsC". Alternatively, if triphenylmethyl chloride is treated with silver perchlorate in a solvent such as THF, the triphenylmethyl cation is obtained. More conveniently, triphenylmethyl salts, PhsC X", can be obtained as orange-red crystalline solids from the action of the appropriate strong acid on triphenylcarbinol in ethanoic or propanoic anhydride solution. The perchlorate, fluoroborate and hexafluoro-phosphate salts are most commonly used for hydride ion abstraction from organic compounds (e.g. cycloheptatriene gives tropylium salts). The salts are rather easily hydrolysed to triphenylcarbinol. 

The following compounds have been obtained from thiete 1,1-dioxide Substituted cycloheptatrienes, benzyl o-toluenethiosulfinate, pyrazoles, - naphthothiete 1,1-dioxides, and 3-subst1tuted thietane 1,1-dioxides.It is a dienophile in Diels-Alder reactions and undergoes cycloadditions with enamines, dienamines, and ynamines. Thiete 1,1-dioxide is a source of the novel intermediate, vinylsulfene (CH2=CHCH=SQ2). which undergoes cyclo-additions to strained olefinic double bonds, reacts with phenol to give allyl sulfonate derivatives or cyclizes unimolecularly to give an unsaturated sultene. - Platinum and iron complexes of thiete 1,1-dioxide have been reported. 

Although the chemistry of zirconium in its lower oxidation states is still relatively unexplored, it is developing. Examples which offer the possibility of further exploitation include the blue, paramagnetic zirconium(III) compound 32) [L2Zr(/r-Cl)2ZrL2] L = C5H3(SiMe3)2-l,3, and the sandwich and half-sandwich compounds derived from cycloheptatriene red... 

One compound, either 7-bromo-1,3,5-cycloheptatriene or 5-bromo-1,3-cyclopentadiene, dissociates into ions when dissolved in water. Which molecule do you think displays this behavior How do you think the other molecule behaves when mixed with water ... 

Oxepin and its derivatives have attracted attention for several reasons. Oxepin is closely related to cycloheptatriene and its aza analog azepine and it is a potential antiaromatic system with 871-elcctrons. Oxepin can undergo valence isomerization to benzene oxide, and the isomeric benzene oxide is the first step in the metabolic oxidation of aromatic compounds by the enzyme monooxygenase. 

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. 

Diazomalonic esters serve as intermediates for the synthesis of a wide variety of compounds including cyclopropanes, cyclo-propenes, cycloheptatrienes, sulfur ylides, lactones, and substituted malonates. ... 

Only one example is known so far, namely the parent compound 22. As already mentioned, cycloheptatriene affords the norcaradiene endoperoxide (Eq. 13) and the tropilidene (2 + 4)-endoperoxide (Eq. 15) however, another major product is the tropilidene (2 + 6)-endoperoxide (Eq. 17)... 

With l,3>5-cycloheptatriene 2 can be trapped to yield four isomeric [2+2] adducts and the exo/endo isomeric [6+2] compound 16. Heating this mixture to 110°C leads to the complete transformation of the silacyclobutanes into 16 via a dipolar intermediate. The attempted synthesis of the diphenyl derivative of the [2+2] products leads to the stereospecific formation of endo-Yl which could be characterized by X-ray diffraction analysis [4]. 

On the other hand, the anodic oxidation of 1,3,5-cycloheptatrienes is one of the most powerful key tools for the preparation of a variety of non-benzenoid aromatic compounds such as tropylium salts, tropones, tropolones, 2H -cyclohcpta h furan-2-oncs and azulenes14. 

The parent 1,2,3-cycloheptatriene (82), generated as a reactive intermediate from tricy-clus 81, can be trapped with various dienes, but it does not dimerize58. In the presence of Ni(PPh3)4, however, the dimer, i.e. radialene 83 is formed59. Similar to the parent compound (2), it polymerizes on contact with oxygen within a few hours. 

This kind of compound was obtained in the reaction of cycloheptatriene with dichloroazine CF3CC1=NN=CC1CF3 when heated at 70°C. A 1 1 mixture of rearranged adducts 31 and 32 was isolated and this latter compound was obtained as a mixture of two diastereomers in the ratio 77 23 (NMR spectroscopy, yield not given). The formation of these two compounds requires considerable skeletal rearrangement of any initial [3+2] or [3+6] cycloadduct and a satisfactory mechanism cannot be proposed. It was not possible to differentiate between structures 31 and 32 on the basis of the spectral data obtained (Equation 3) <1995JFC203>. 

Homoaromaticity may still result if the delocalization in an aromatic compound is interrupted by more than one saturated linkage. In this case a bis-, tris-, or tetra-, etc., homoaromatic compound results. In the notation of Winstein (1967) the size of the saturated linkage (e.g. -CH2- and -CH2CH2-) is not considered in classifying the degree of homoaromaticity. Only the number of interruptions to delocalization is taken into account. Thus, if cycloheptatriene [5] were homoaromatic, it would be monohomobenzene. Similarly, all m-l,4,7-cyclononatriene [8] could be named trishomobenzene if homoaromatic. 

TABLE 4. 13C chemical shifts of cycloheptatriene and norcaradiene compounds... 

Conjugated dienes yield mono-adducts with dihalocarbenes at the more electron-rich C=C bond further reaction at the less reactive bond may also occur [e.g. 4,8,19, 23, 31, 37, 49, 62, 69, 94]. Cycloheptatriene yields the syn- and nnti-1,2 5,6-bis-adducts (14.5 and 22.9%) and the syn-1,2 5,6-ann -3,4-tris-adduct with dichloro-carbene [62], The facile reaction of cyclopropylethenes with dihalocarbenes produces dicyclopropyl compounds [53, 117]. Isoprene reacts with chloro(phenylthio)carbene across the more reactive 1,2-bond (51%) [146]. 

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