Phenanthrene cyclization

Calculations at the 4-31G level of theory found that the 1,2-bis-carboxonium ion (72) is significantly more stable than the carbenium-carboxonium dication (73). Thus, when compared with the 1,1-dihydroxylie structure 73, the 1,2-dihydroxy lie structure 72 is more effective at stabilizing the 1,2-ethylene dication. This effect leads to the stabilization of dication 71 (eq 16), and not to phenanthrene cyclization. 

Photocyclization of 1-benzylideneisoquinolines to the Aibexao[d,e,g -quinolines is a well-studied example of the above stilbene-phenanthrene cyclization and therefore has been extended to the development of new photochemical methods for the synthesis of aporphine alkaloids (11-14). In this section, photocyclization of 2-acyl-1 -benzylideneisoquinolines to dehy-droaporphines and their subsequent conversion to aporphines and oxo-aporphines are summarized. 

All the previously reported examples of photoaddition of acetylenes to benzene involve 1,2-cycloaddition and subsequent formation of cyclo-octatetraenes10 (but see ref. 43 for a discussion of the addition of perfluorobut-2-yne to benzene). The report of 1,3-cycloaddition of diphenylacetylene to the trimethyl ester of trimesic acid, is, therefore, of interest as this leads directly to the semibullvalene system.44 The reaction apparently requires 6 days, the yield of the product is low, and the adduct (28) is not isolable in the pure state. The triethyl ester and the acetylene also yield (29) via a stilbene-phenanthrene cyclization of the primary... 

Many heterocyclic analogues of the stilbene-phenanthrene cyclization have been reported, and the utility of enamide and dienamide photocyclizations has been dealt with in comprehensive reviews. Only a few selected examples will be mentioned here. 

This cyclization also gives good results in the case of derivatives of naphthalene, anthracene, phenanthrene, and other aromatic substrates [76]... 

Cyclization reactions of unsubstituted phenanthrene-9,10-dicarbonitriles or of 2,7-di-/erf-butyl-phenanthrene-9,10-dicarbonitrile lead to phenanthrenocyanines. 

Poly(arylene ether ketone)s can also be modified by introducing the functional groups using similar approaches to polysulfones. For example, poly(arylene ether ketone)s were sulfonated.189 In addition, o-dibenzoylbenzene moieties in the poly(arylene ether)s can be transformed to heterocycles by cyclization with small molecules. These polymers can react with hydrazine monohydrate in the presence of a mild acid in chlorobenzene or with benzylamine in a basic medium.190 Another example of the use of the o-benzyl cyclization strategy is the intramolecular ring closure of poly(arylene ketone)s containing 2,2/-dibenzoylbiphenyl units to form poly(arylene ether phenanthrenes).191... 

PET reactions [2] can be considered as versatile methods for generating radical cations from electron-rich olefins and aromatic compounds [3], which then can undergo an intramolecular cationic cyclization. Niwa and coworkers [4] reported on a photochemical reaction of l,l-diphenyl-l, -alkadienes in the presence of phenanthrene (Phen) and 1,4-dicyanobenzene (DCNB) as sensitizer and electron acceptor to construct 5/6/6- and 6/6/6-fused ring systems with high stereoselectivity. 

Catalytic quantities of transition- or non-transition metals promote the cyclization of 2-alkynynylbiphenyl analogs to phenanthrene or fulvene analogs. The mechanism is thought to involve activation of the alkyne by metal coordination, prior to cyclization (Equations (179) and (180)).146... 

Takasu et al. found that at high temperature a free radical reaction of polyolefinic vinyl iodides leads to phenanthrene derivatives via a 6-endo-6-exo-polycyclization while at low temperature a mono-cyclized product is obtained through a 5-exo mode.1501... 

The ability to cyclize to a phenanthrene has been employed in analytical procedures for tamoxifen (69). The drug was irradiated at 254 nm in dioxane-heptane solution and the assay based on the fluorescence of the product (70) [57]. Another group ran the tamoxifen on a TLC plate which was exposed to a UV lamp for some minutes before assaying in a densitometer [58]. 

Oxidative cyclization, substituted stil-benes to phenanthrenes, 46, 91 4-Oxo-l, 1-dimethyIpiperidinium salts, 46,82... 

Several tetra- and pentacyclic systems were prepared from Pro, which was first -substituted with naphthalene or phenanthrene rings whereupon the cyclization took place. Such reactions were used for synthetic ap-proaehes toward alkaloids vinceten from Cynachum vincetoxicum (the tetrahydrobenzo /]pyrrolo[l,2-Z ]isoquinoline system 146) (79LA1212 84AJC819) or tylophorine (65T2573). 

The valence tautomerism 251 257 has been proposed to account for the formation of iV-methylthiobenzamide by irradiation (2537 A) in methyl cyanide solution. The valence tautomer 257, R = Me, = Ph, has been detected spectroscopically (p , 2060 cm —N=C=S) either during photolysis at 25° or by heating at 160°. Photochemical oxidative cyclization of 4,5-diaryl derivatives (251, R = R = Ar) analogous to the formation of phenanthrene from stilbene has been reported. Thus, irradiation of the 4,5-diphenyl derivative 251, R = R = Ph, yields the tetracyclic meso-ionic compound (258). ... 

In the presence of an oxidizing species (oxygen, iodine, tetracyanoethylene and others) DHP is dehydrogenated into phenanthrene. This oxidation can also be thermal or photochemical. In general, meta substituted stilbenes give rise to two isomeric substituted phenanthrenes ortho-substituted stilbenes can lose the substituent on cyclization. 

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