Benzo biphenylenes

Benzo[ ]biphenylene [259-56-3] M 202.2. Purified by sublimation under reduced pressure. 

Benzo[ ]biphenylene [259-56-3] M 202.2,242.6-243.6 . It forms yellow ciystals from C6H6/cyclohexane m 234-245° (sublimation). The 2,4,7-trinitrofluorenone complex ciystallises as red needles from C6H6/MeOH m 214-216°. It has been sublimed in vacuo. [Jensen Coleman Tetrahedron Lett No 20 7 1959, Barton et al. J... 

Rates of detritiation of the 1 and 2 positions of biphenylene and the 5 position of benzo [bjbiphenylene by lithium cyclohexylamide at 50 °C relative to benzene have been determined as 490, 7.0, and 1,865, respectively and the enhanced reactivity of the position a to the strained 4-membered ring has been attributed to the enhanced electronegativity of the strained bridgehead carbon atom. The same... 

Bei der Reduktion von 1,2-Dibrom-benzocyclobuten wird als einziges Dimerisations-produkt 6a,lOb-Dihydro-(benzo-[a]-biphenylen) isoliert5 ... 

Perchlorotriphenylene has been reported in the literature and said to show severe molecular twisting, however, recent work suggests this molecule has not actually been isolated with perchlorofluorene-9-spirocyclohexa-2, 5 -diene being formed instead. The X-ray stmcture of the linear [3]phenylene (benzo[3,4]cyclobuta-[l,2-b]biphenylene, 44) has been obtained, and it shows a relatively large degree of bond alternation while the center distorts to a cyclic bis-allyl frame. ... 

In a conventional seven-step synthesis beginning with biphenylene, biphenylene-2-acetonitrile (100), mp. 105—107°, was prepared. It condenses readily with (7) to the orange-yellow aminonitriles (101) (not isolated). In accordance with the MO calculation the ring-closure to the benz(b)biphenylene-6-carbonitriles (102) is strongly favored, theoretically by 0.211 / (Section II. C., Fig. 1 VIII), over the isomeric benzo(a)biphenylenes of which no traces could be detected in the reaction products59. By hydrolysis and decarboxylation (102 a) was converted to benzo(b)-biphenylene, mp. 236-237°, Ref. 242-243°60). 

R —Benzo(b)biphenylene-6-carbonitrile Yield Components (°C) Time... 

This method was first applied to relative electron affinities of substituted nitro-benzenes. All but one of these has been measured by HPMS TCT studies. However, the Ea of s-butyl nitrobenzene has only been determined by collisional ionization and is still listed in the NIST tables as 2.17(20) eV. This value is referenced to a high value for nitrobenzene and should be about 1 eV lower [60]. The electron affinities of aromatic hydrocarbons have been reported using the collisional ionization method. The value for biphenylene is larger than that obtained from half-wave reduction potentials. The values for pyrene, anthracene, and c-CgHg are consistent with other reported values, but the values for benzanthracene, coronene, and benzo[ghi]perylene are significantly lower than the largest precise value and are attributed to excited states. 

The mass spectrum of benzo[c]cinnoline ° shows a main initial loss of N2 from the molecular ion (m/c 180) to give a biphenylene radical ion mje 152 base peak), which probably has the open structure 39, as postulated... 

The ready loss of nitrogen from the parent ion in the mass spectrum of benzo [c] cinnoline (Section III,D) has a parallel in its thermal decomposition on vacuum pyrolysis at temperatures above 800°C it is converted into biphenylene (86) in high yield [Eq. (15)]. The absence of by-products in... 

Phenazine is similarly unreactive toward benzyne (by oxidation of 9), which gave only biphenylene and small amounts of unidentified highly colored products.81 On the other hand, the benzo[h]quinolizinium salt 175 reacts like anthracene with benzyne (generated by aprotic diazotization of anthranilic acid in refluxing acetonitrile) to give the Diels-Alder adduct 176 (78%).100 Aromatization of 176 to 9-(2-pyridyl)anthracene (177) is accomplished in refluxing acetic anhydride in the presence of sodium acetate. 

The simplest 4 system is cydobutadiene (in which n = 1), which is an extremely unstable compound. It can be stabilized by metal complexation. One method of stabilizing cydobutadiene is by means of weU-chosen substituents, for example, diethyl 2,4-bis (diethylamino)cyclobutadiene-l,3-dicarboxylate (20) is reasonably stable, melting at 52 °C, and the ring is square planar. Benzo-annelation has also been used as a method of stabihzation. Biphenylene (21) has long been known, and l,2-diphenylnaphtho[f)]cydobutadiene (22) is now known (Figure 7.10). 

In the linear isomer the naphthalene moiety is fused by its 2,3-bond to the four-membered ring and in the angular isomer by its 1,2-bond. The 1,2-bond of naphthalene has more double-bond character than the 2,3-bond, hence angular annelation of a benzene ring onto biphenylene will tend to induce more double-bond character into the four-membered ring compared to biphenylene itself. The converse situation obtains in linear annelation. Since increase in double-bond character in the four-membered ring lowers its stability we can simplistically predict that benzo[6]biphenylene (XXVII) will be more stable than biphenylene which is in turn more stable than benzo[a]biphenylene. This argument is supported by molecular orbital calculations [187]. 

Bicyclo[6.3.0]undecapentaenium salts, 390 Biphenylene, 221 preparation, 222 reactions, 224 acylation, 226 with carbenes, 228 electrophilic substitution, 224 halogenation, 225 homolytic substitution, 228 lithiation, 227 mercuriation, 226 nitration, 224 with nucleophiles, 227 oxidation, 224 photolysis, 228 reduction, 224 thermolysis, 228 Biphenylenes, benzo, 230 Biphenylene dianion, 229 Biphenylene dication, 229 Biphenylenes, heterocyclic analogues, 233... 

Vacuum pyrolysis of benzo[c]cinnoline provides biphenylene in high yield [143] ... 

Benzo[fl]biphenylene [252-47-1] M 202.2, m 72-73° (compare with p-isomer). It forms yellow needles from MeOH and snblimes in vacuo (m 72.0-72.8°). The 2,4,7-trinitrofluorenone complex crystallises as black needles m 201.5-202.5°. [Cava Stacker JAm C/zem 80c 77 6022 7955, Barton et al. JChemSoc(C) 1276... 

Thus, by measuring the values for Jz -i and in any benzannulene 25 and use of this equation to calculate bond orders and then Q, a statement as to whether the annulene is aromatic, antiaromatic, or nonaromatic in nature can be made. From a simple viewpoint, if in 25 J2.3 > Jza (see naphthalene, for example, in Scheme 10), then the [A/ -annulene is aromatic, while if J3 4 > 2,3 (for example, the values in biphenylene (28) are 8.24 and 6.80 Hz, respectively), then the [A/ -annulene is antiaromatic (in that case the [A/ -annulene is benzocyclobutadiene). In the subsequent paper,this method was used to compare the ions of small benzannulenes, including benzan-nelated cyclopentadiene (indenyl anion, 29), benzo-tropylium ion (30), and benzocyclooctatetraene dianion (31), which all had Rvalues indicating strongly aromatic systems. That found for benzocyclooctatetraene itself (32) fell in to the nonaromatic range, as might be expected for the tub structure (Scheme 13). 

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