Triphenylenes, formation

Figure 47 Mechanism of triphenylene formation in polymer 343. (From Ref. 212.)...

Acetylene dicarboxylate and maleic anhydride failed to react with simple methylene cyclopropenes, but reacted readily with calicene derivatives, as shown by Prinz-bach293. Thus ADD combined with benzocalicene 497 to give the dimethyl tri-phenylene dicarboxylate 499, whose formation can be rationalized via (2 + 2) cycloaddition across the semicyclic double bond as well as (4 + 2) cycloaddition involving the three-membered ring (498/501). The asymmetric substitution of 499 excludes cycloaddition of ADD to the C /C2 triafulvene bond (500), which would demand a symmetrical substituent distribution in the final triphenylene derivative. 

For the triphenylenes discussed above, the only interactions that are involved in the formation of the columns are the arene-arene interactions which, although being strong, are generic and do not have positional information. Additional specific interactions are necessary to keep the molecules positionally ordered with respect to each other and to create chiral columns, as will be discussed in the next sections. 

The photolysis of 4-nitroanisole in degassed acetonitrile or benzene yields 4-nitro-soanisole and 2-nitro-4-methoxyphenol is). Triphenylene (Et = 67 kcal mole i 4-nitroanisole t=59.5 kcal mole i has been used to sensitize the reaction, which is suppressed completely by nitric oxide. A rationale for the formation of the products observed is given below. 

The products formed upon direct irradiation of 1 include 9-phenanthrol and fluorene. The former is believed to be formed in a triplet process. This is supported by the capacity to quench phenanthrol formation with tram-1,3-pentadiene and to circumvent the rearrangement to 292 (R = H) by utilization of sensitizers such as benzophenone or triphenylene. In an attempt to confirm that the chemically significant excited state in the conversion of 1 to 292... 

Bushby has examined the FeCl3-mediated oxidation of hexyl-protected (Hex) phenol ether units in the preparation of triphenylene-based liquid crystals [63]. This strategy allows the formation of unsymmetrically substituted products 75a-l (Table 18) [64]. The use of methanol in the work-up is critical in order to obtain the products in good yield. If the protecting group on the phenol component is isopropyl (74m), the coupling reaction occurs to give the unprotected phenols 76a-c directly (Scheme 17) [65]. 

An organocopper intermediate was detected by Lewin and Cohen in the reaction of / -iodotoluene with copper in a good complexing solvent (184). Analysis of protonated aliquots from a reaction performed in quinoline indicated an accumulation of />-tolylcopper to a maximum of 43% after 95 hours, at which point the iodide was consumed, and then a slow decrease to by dimerization. Other experiments also indicate the formation of an arylcopper compound in Ullmann reactions (127,141, 210). The isolation of deuterated products, presumably from the decomposition of an intermediate organocopper species in deuterated benzene and cyclohexane, suggested decomposition to free radicals (127). Decompositions of certain o-haloarylcopper intermediates by a benzyne mechanism cannot be totally excluded. The formation of a dichlorobenzene and by-products such as dibenzofuran and triphenylene from only the ortho isomer of the chloroiodobenzenes in Ullmann coupling reactions (210)... 

These systems exhibit considerable affinity for halide anions. X-ray analysis ascertained the formation of an anionic 2 1 chloride adduct of (1) where the chloride is simultaneously bound by four mercury atoms. In the crystal structures of (2) Cl and (2) l2, the anions are located within the macrocycle and complexed cooperatively by the four mercury(II) centers. Several anionic complexes of (3), including bromide, iodide, and thiocyanide salts, have been isolated. The compounds adopt multidecker stmctures with the hexacoordinated anions effectively sandwiched between two successive molecules of (3). The Lewis acidity of perfluoro-ortAo-phenylenemercury (3) has also been substantiated by its ability to form stable adducts with neutral substrates (HMPA, DMSO, ethyl acetate, and acetonitrile) and arenes. The (3) -CeHe adduct exists as extended stacks of nearly parallel, staggered molecules of (3), which sandwich benzene molecules. Similar structures have been reported for the corresponding adducts with biphenyl, naphthalene, pyrene, and triphenylene. 

Irradiation of the pyrimidines (241a,b) using triphenylene-sensitization in tetrahydrofuran results in their conversion to the spirotriketones (242). The path by which this occurs involves fission of bond a in (241) affording a biradical which cyclizes to the observed products (242). The evidence for a biradical intermediate is supported by the formation of (243) from the irradiation of pyrimidine (241c). This product arises by hydrogen abstraction within the biradical formed by the fission of a followed by a free radical hydroxyl at ion. The source of the hydroxyl radical is thought to be the peroxide of tetrahydrofuran produced in the reaction mixture. ... 

The coelectrolysis of veratrole with anisole derivatives afforded in TFA-CH2CI2 good yields of aryl-substituted triphenylene derivatives (Table 4, number 9). Product formation probably occurs by initial coupling of the veratrole cation radical with anisole to an unsymmetrical dimer. This is followed by coupling of the dimer and intramolecular cyclization to the product. 

A special reaction of this type is the formation of benzyne. o-Fluorobromobenzene reacts with lithium amalgam in ether or furan with an intermediate formation of benzyne. In the former medium, diphenylene and small amounts of triphenylene and 9,10-dimer-cura-9,10-dihydroanthracene were formed, whereas the major product (76%) in furan was 1,4-dihydronaphthalene-1,4-endoxide [64]. 

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