Synthesis of Substituted Phenanthrenes

CH2CI2, rt, 20 min., then DDQ, CgHg, reflux (82% over 2 steps). 

SCHEME 17.8 Synthesis of substituted naphthalenes from 1,2-diiodobenzenes—application of allylboronic acid pinacol ester. (Adapted with permission from Ref. [10]. Copyright (2009) American Chemical Society). 

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A synthesis of substituted phenanthrenes has been reported using the bicyclooctadienes (61) as starting material. The process makes use of the nucleofugal group on C-8 and follows the path outlined in Scheme 3. This involves a di-rr-methane bridging process followed by the collapse of the intermediate biradical (62). Normal di-Ti-methane behaviour is reported in the acetophenone-sensitized irradiation of the isoquinolinone derivative (63a). This yields the two products (64) and (65) as a 3 1 mixture in a total yield of 75%. An N-oxide derivative gave a brown polymer with little evidence for the formation of di-n-methane products. The influence of ring substituents was also studied for the derivatives (63b, d) and the results of this are shown in Scheme 4. The authors conclude that the cyclization process is under LUMO control. Irradiation of the dihydropyridine (66) affords the oxidised pyridine (67) as the major product. A minor product (68) is also formed by a di-ir- methane process. ... 

A domino synthesis of substituted phenanthrenes 28 was achieved by Dalle-magne and coworkers [28] through reaction of 2-(2-bromophenyl)acetates 26 and cyanoboronic ester 27 (Scheme 12.10). The reaction resulted in the desired products in 60-87% yields through a Suzuki-Miyaura cross-coupling followed by a Dieckmann-Thorpe ring-closure reaction. 

Scheme 6/1.86. Synthesis of substituted 5,6-dihydro-8/-/-[5,7-a]diazacyclohepta[/7c] phenanthrene-4,7-diones.

The method has been applied to the synthesis of a range of substituted phenanthrenes and has the merit that it involves fewer steps than, for example, the Haworth synthesis. Good results are not always obtained, however, when some electron-withdrawing substituents (e.g. N02, Me CO) are present. 

The reaction of ozone with an aromatic compound is considerably slower than the reaction with an alkene. Complete ozonolysis of one mole of benzene with workup under non-oxidative conditions will yield three moles of glyoxal. The selective ozonolysis of particular bonds in appropriate aromatic compounds is used in organic synthesis, for example in the synthesis of a substituted biphenyl 8 from phenanthrene 7 ... 

General procedure for the reaction of an o-substituted aryl iodide with a diarylacetylene. Synthesis of phenanthrene derivatives. 

The synthesis of li7-cyclopropa[/]phenanthrene (142) presented unexpected difficulties and met many failures. Early approaches used a variety of schemes which were not adequate for this highly reactive compound and invariably produced ring-opened products. Thus irradiation of the substituted indazole 138 resulted in nitrogen extrusion and formation of the biradical 139, which reacted with the solvent, benzene, to form 140. The desired cycloproparene 141 was not formed. Ring contraction of 144, in turn, produced derivatives of 9-phenanthroic acid, the formation of which was shown not to involve phenanthrocyclopropenone (143). °° The attempted 1/3/elimination of 145 was similarly unsuccessful and afforded no 142. ... 

The attempted synthesis of [njcyclophenacenes has also been reported. Kuwata-ni and coworkers reported the synthesis of a pentabenzo[20]annulene, as a possible precursor to [10]cyclophenacene (Scheme 2.3) [16]. Light-induced electrocycli-zation of the precursor was unsuccessful because of isomerization of the (Z)-olefin into the (E)-olefin, which undergoes an undesirable transannular reaction [17]. St. Martin and Scott tried to synthesize [12]cyclophenacene, but attempts at the macrocyclic oligomerization of substituted naphthalene and phenanthrene building blocks by flash vacuum pyrolysis method were unsuccessful [18]. 

A general method for biaryl coupling has been limitedly used for tri-ort o-substituted biaryls. A phenanthrene-based ligand exceptionally allowed the synthesis of sterically hindered biaryls where each reactant possesses two ortfo-substituents (Equation (205)).879... 

Pschorrphenanthrene synthesis. Although use of sodium iodide rather than copper powder generally improves the yield in the synthesis of phenanthrenes from diazonium 2-amino-a-phenylcinnamic acids (3, 267), yields are poor when the acceptor ring is substituted by electron-donating alkoxy groups, which are often present in natural phen-... 

Many completely aromatic polynuclear hydrocarbons are readily formed by cyclization of aryl-substituted aldehydes, ketones, or related compounds. The simplest case is the formation of naphthalene by refluxing (fi-styrylacetaldehyde, C HsCH = CHCH2CHO, with hydrobromic acid-acetic acid mixture. " The ring closure has found extensive use in the synthesis of 9-alkyl- and 9 aryl-anthracenes and phenanthrenes. " ... 

Therefore, the method described allows a novel economic as well as ecologically sound synthesis of quinone derivatives. Higher condensed arenes, e.g., anthracene, are converted to the quinones or cleaved to dicarboxylic acids, as in the case of phenanthrene (yield ca. 50 %). Besides MTO, in principle all alkyl- and to some extent also aryl-substituted trioxorhenium compounds, e.g., cyclopropylrhenium trioxide or cyclopentadienylrhenium trioxide, can be used as active catalysts. However, until now MTO apparently constitutes the most active and easy-to-handle catalyst (see Figure 1, p. 439). The solvent of choice for the reaction and the workup procedure, is concentrated acetic acid, also used to dilute the H2O2 (85 wt.%), yielding a water-poor reaction medium which is advantageous for the catalyst lifetime. 

Table 1 IRa Spectroscopic data and melting points,6 and references for the synthesis and crystallography of substituted phenyl (pcydH), biphenyl (bpcydH), naphthalene (nacydH), phenanthrene (phcydH), pyrene (pycydH) and fluoren-9-one (flcydH) cyanamides, substituted 1,4-dicyanamidebenzene (dicydH2) derivatives, 4,4 -biphenyldicyanamide (bpdcydH2) and azo(diphenyl) mono- (apcH) and di-cyanamides (adpcH2).

Synthesis of polycyclic compounds. 2,2 -Bisbramomethyldiphenyl (1) reacts with 1 mole of triphenylphosphine to give the phosphonium salt (2), which is converted into the ylide (3) on treatment with base (sodium methoxide). The ylide (3) is not isolated but undergoes intramolecular C-alkylation to form the phosphonium salt (4). This salt on treatment with phenyllithium gives the ylide (5). This ylide is readily transformed into phenanthrene or 9-substituted phenanthrenes.3... 

Substituted phenanthrenecarboxylic acids can be obtained in this way and yield the phenanthrene hydrocarbons on decarboxylation. Weisbach and his co-workers803 applied this reaction to synthesis of aporphine. 

Electrocyclization - helicenes. Brief cover reviews of the synthesis of helicenes were published.In the formation of helicenes and substituted phenanthrenes via the photochemical electrocyclization of diaryl-ethenes in the presence of iodine as an oxidant, the addition of THF... 

In all cases presented above, annulation reactions were limited to intramolecular arrangements. There are also transformations involving two independent reaction partners. In 2005 a Cr-mediated synthesis of PAHs from halobiaryls was published [94]. The 2,2 -dihalobiaryl starting material 150 is first treated with BuLi before addition of the Cr reagent. Final treatment with an acetylenic reaction partner delivers the phenanthrene core 151 (Scheme 38). Recently, Wu and coworkers presented a Pd-catalyzed version starting from 2,2 -diiodobiphenyls to access substituted phenanthrenes [95]. 

With unsymmetrical olefins, formation of multiple products is possible due to the availability of multiple sites for cyclization as illustrated in the synthesis of [6]helicene (Scheme 16.12) [15]. Out of the four possible products (bond formation between a-c, a-d, b-c, and b-d), two are formed (bond formation between a-c and b-c) of which one of them is [6]helicene (Scheme 16.12). When a more symmetrical phenyl-substituted derivative was used, [6]helicene was formed exclusively (Scheme 16.12) [15]. Synthesis of the higher homologue, namely, [ll]hehcene, is illustrated in Scheme 16.13. From both the reactions given in Scheme 16.13, it is evident that the bay region carbons of phenanthrene and benzophenanthrene are more reactive for electrocychzation [16]. 

The King group has used the same principle for the synthesis of phenanthrene 52 from 53, using both 2-Ru and 3-Mo as catalysts for the RCM reaction. Initially, a Suzuki-Miyaura coupling strategy, as shown in Scheme 17.9, was utilized between the substituted styrenes 54 and 55 to synthesize the biphenyl 53, which was subsequently cyclized [24] (see Ref. [25] for a related strategy). 

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