Dibenzo systems

Reductive cyclization of 2-(o-benzoylphenyl)benzotriazole with triethyl phosphite gives the phenyl derivative of the isomeric dibenzo system (176) (74CL951). 

Direct X-ray evidence shows that iV-methyl-5,6-dihydro-7//,12//-dibenz[c,/]azocine exists in the crystalline phase as the rigid plane-symmetrical boat-chair (468) (74AX(B)1670). In contrast, the iV-t-butyl analog exists as enantiomeric pairs or twist-boats (469) (74AX(B)1674>. The first observations of dynamic NMR effects in the angularly fused dibenzo system were made on compounds closely related to (468) and (469), namely (470a-c) (70T1275). 

Pyridine, the diazines, 1,3,5-triazine, 1,2,4,5-tetrazine, quinoline, isoquinoline, quinolizinium ion and the benzodiazines are HtiCKEL-aromatic systems (heteroarenes). 2//-Pyrane, 4//-pyrane and the corresponding benzo compounds, 1,4-dioxin, 1,4-dithiin and 1,4-oxathiin are not aromatic. However, the cations derived therefrom, like pyrylium and thiinium cations or dioxinium and dithiinium dications are aromatic the same is true for the corresponding benzo or dibenzo systems (e.g., benzopyrylium). Phosphinin is characterized by a specific heteroaromatic situation. 

It is interesting to compare the dimensions of the monocyclic systems with those recorded for their dibenzo counterparts where the aromatic nature of the heterocyclic ring is expected to be much diminished. Comparison of the data in Table 4 with that in Table 2 shows that... 

These results the authors consider cannot be aeeounted for on the basis of a 6-membered ring B and the adoption of a 5- or 7-membered ring B introduces a difficulty in explaining the formation of 2 3 4 7-tetramethoxyphenanthraquinone in the oxidation of deaminocolchinol methyl ether. There is, however, a precedent in Weitzenbock s oxidation of 4 5 6 7-dibenzo-d -c /cZoheptatriene-l-aldehyde (X) to phenanthraquinone, for representing the a -unsaturated ketone as 9 12 13 14-tetramethoxy-3 4 5 6-dibenz-d -c /cZoheptatriene-7-one (XI CH2 at —> CO), using the system of numbering adopted by... 

The oxoaporphine alkaloids Teliglazine (126), Corunnine (127), Nandazurine (128), PO-3 (129), A-Methylliriodendronine (130), and A,(9-Dimethylliriodendronine (131) contain the 6-methyl-7-oxo-dibenzo [Je,g]quinolinium-l-olate ring system 125 which is isoconjugate with the l-methyl-7-methylene-7H-benzo[Je]anthracene anion (Scheme 46). Therefore, these alkaloids belong to class 1, i.e., heterocyclic mesomeric betaines isoconjugate with odd alternant hydrocarbon anions. Another... 

The central C-C double bond of dibenz[, /]oxepin displays the properties of an activated aromatic system and undergoes substitution reactions. Nitration and acid-catalyzed dcutcration gives the dibenzo[i>,/]oxepins 1 with the respective substituent in position 10.161... 

According to the Hantzsch-Widman system, the seven-membered unsaturated hcterocyclc with one sulfur atom is named thiepin (1). The three different benzothiepins are assigned by the position of sulfur 1-benzothiepin (2), 2-benzothiepin (3) and 3-benzothiepin (4). Of the four possible dibenzothiepins only dibenzo[6,r/]thiepin (5) and dibenzo[A,/]thiepin (6) are of importance for synthesis, while the other two isomers, which contain unfavorable o-quinoid structures, exist mainly as the stable dihydro compounds, i.c. 5,7-dihydrodibenzo[c,t ]thiepin (7) and 6,1 l-dihydrodibenzo[6,c ]thiepin (8). Benzannulation over all double bonds results in tri-benzo[6,(7,/]thiepin (9). 

Reduction should result in l,2-dihydro-l,2-diazocine (2) which formally contains a cyclic, conj ugatcd 10 7r-electron system and potentially possesses aromatic character. To date, however, only the synthesis of a dibenzo derivative has been described (see Section 1.2.1.3.). 

Hydrazine reacts with biphenyl-2,2 -dicarbaldehyde (3, R = H). under elimination of nitrogen, to give phenanthrene,17 most probably not via the intermediate formation of a diazocine system. With other 2,2 -diacylbiphenyl compounds the expected dibenzo[[Pg.520]

Reaction of the biphenyl-2,2 -diamine 1 with oxalyl chloride leads to the dibenzo[< ,g][l,4]di-azocine system 2.19... 

The unsubstituted parent 1,5-diazocine (1) is hitherto unknown. Benzannulated systems, however, have been prepared, particularly dibenzo f>,/][l, 5]diazocine and its derivatives which have been intensively investigated due to their pharmacological properties. So far, all compounds synthesized show no evidence for delocalization of the 7t-electrons. One special review on the chemistry of 1,5-diazocines is available.1... 

From the general structure of 1,2-diheterocines 1 with identical heteroatoms other than the scries with two nitrogen atoms (X — NR, which have already been discussed in Section 1.2. as they can be regarded as 1,2-dihydro-l, 2-diazocines), only one other example of such a 1,2-di-hcterocine system exists i.e. dibenzo derivative 4 containing the 1,2-dithiocin system 2.1... 

Dibenzo[c,g][l,2]dithiocin (4) can be readily prepared by reductive cyclization of the dithiol 3. On the basis of the electronic spectrum analysis it can be concluded that there is no conjugation in the 8-membered ring system of dibenzo[c,g][l,2]dithiocin (4).1... 

The dibenzannulated system dibenzo[ /]thionin (6) is prepared by a twofold Wittig reaction... 

The only 5//-1,3,6-triazonine system which has been reported and is fully supported by spectral data and elemental analysis is obtained by reaction of the imine 1 with chloroacetic acid and polyphosphoric acid.22 From a mixture of products, 2-chloro-6-(chloromethyl)-13-phenyl-dibenzo[e/, h [, 3,6]triazonine (2) was separated by silica-gel flash chromatography in poor yield. 

The 3,4-didehydro-27f-l-benzopyran (4), generated when 3,4-dibromochromenes are treated with organometaUic reagents, reacts with dienes to give the dibenzo[6,d]pyran system <96TL1313>. 

Kuhn s carbanion, the all-hydrocarbon anion tris(7//-dibenzo[c,g]-fluorenylidenemethyl)methanide ion [2 ] (Kuhn and Rewicki, 1967a,b), is a stabilized system with tt electrons widely spread over the sp hybridized carbon framework, and was isolated as the potassium salt. It also appears in DMSO solution by dissolving the parent hydrocarbon, resulting in a deep green colour. The pKg value of the precursor hydrocarbon [2]-H is 5.9 in aqueous HCl-DMSO (Kuhn and Rewicki, 1967a,b), and its enormous stability, as compared with cyclopentadiene [9]-H, pKa 18 in DMSO... 

The chemical name of A9-THC according to the dibenzopyrane numbering system is 3-pentyl-6,6,9-trimethyl-6fl,7,8,10fl-tetrahydro-6H-dibenzo-[b, d]pyran-l-ol as depicted in 1.1 (Fig. 1). 

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