Dibenzobicyclo octatrienes

The dibenzobicyclo[2.2.2]octatriene system (71) essentially involves interaction of three composite n orbitals, i.e., the olefinic n orbital as the reaction center, and two aromatic k orbitals. A simplified interaction network, i.e., two n component systems free from steric bias, is intriguing. In this context the facial selectivities of... 

The Diels-Alder reactions of anhydrides based on a dibenzobicyclo[2.2.2]octatriene motif 88a-88e, as non-sterically biased dienophiles, were studied [151]. 

Therefore, the preference of the cycloadditions is opposite in direction to the biases observed in nucleophilic additions of 2-substituted 9,10-dihydro-9,10-ethanoanthracen-11-ones (34) (dibenzobicyclo[2.2.2]octadienones) and in electrophilic additions of 2-substituted 9,10-dihydro-9,10-ethenoanthracenes (dibenzobicyclo[2.2.2]octatrienes) 71 [103]. 

Isolation of another set of three rotamers, but without recourse to optical resolution, was accomplished by Yamamoto and Oki (143) by suitably modifying the dibenzobicyclo[2.2.2]octatriene. The constitution of the compound separated is dimethyl 2,3-dichloro-9-(l,l-dimethyl-2-phenylethyl)-9,10-dihydro-9,10-eth-enoanthracene-11,12-dicarboxylate (100). It should possess three diastereomeric... 

Recently the group of D. W. Armstrong exploited the enantiopure ionic liquid 76 in the photoisomerization of dibenzobicyclo[2.2.2]octatrienes, and up to 12% ee was reported (Scheme 83). The obtained ee was possible due to the addition of base in order to deprotonate the carboxylic acid function of 74 resulting in a strong anion-chiral cation interaction. In the absence of a base, lower values of ee were obtained, and in the case that ester functions instead of carboxylic acid groups were present in the molecule, only racemic product was found. Ionic liquid 77 gave up to 6.8% ee. 

The effect of a remote substituent on the facial selectivities in a nucleophilic conjugate addition has been investigated for the reaction of EtSH with a series of dibenzobicyclo[2.2.2]octatrienes (84). Syn-addition proved to be favoured for nitro substituent and polar solvents increased the selectivity (Table 5).19... 

Distortion of olefin tr-orbitals in dibenzobicyclo[2.2.2]octatrienes 4 has been detected37. Thus, nitro and fluoro groups give large to moderate bias with preferred syn attack (with... 

Both trans and cis adducts can be formed in reactions of bicyclo[ 2.2.2]octene ° and related bicyclooct-2-enes °, bicyclo[2.2.2]octadiene °, homobarrelenes or dibenzobicyclo[2.2.2]octatrienes ... 

Skeletal rearrangements are rare, but are found for strained bi- and polycyclic alkenes, e.g., bullvalene , bicyclo[4.2.2]deca-2,4,7,9-tetraene , 4,5-exo-trimethylene-2-norbornene , 6-methylenebicyclo[3.1.1]heptane ", 5-methylbicyclo[2.1.1] hexene N-benzyl-9-aza-bicyclo[4.2.2]deca-2,4,7-triene , dibenzobicyclo[2.2.2]-octatriene derivatives and bornylene ... 

Jie Ding, Vasumathi Desikan, Xinxin Han, et al. Use of chiral ionic liquids as solvents for the enantioselective photoisomerization of dibenzobicyclo[2.2.2]octatrienes. Org. Lett. 2005. 7, 335-337. 

A Japanese group has published several papers on the restricted rotation about the single bond of bridgehead-substituted triptycenes and dibenzobicyclo[2,2,2]-octatrienes, and conformer distributions and structural assignments have been made on the basis of the n.m.r. characteristics. In the 9-benzyltriptycenes, a single pen-substituent relative to the benzyl group results in frozen C-9—C enzyi rotation at low temperatures, and two such substituents hinder rotation at room temperature. " In the case of 9-o-tolyl and 9-o-anisyl triptycene derivatives, e.g. (24), the spectra are interpreted in terms of a back-and-forth rotation rather than a full 360" rotation. " The synclinal rotamer (25) is sufficiently stable to permit resolution [by way of the mono-(—)-menthyl ester] into a pair of enantiomer ([a] + 24.7°). The... 

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