Phenanthrene addition reactions

Both phenanthrene and anthracene have a tendency to undergo addition reactions under the eonditions involved in eertain eleetrophilic substitutions. For example, in the nitration of anthracene in the presence of hydrochloric acid, an intermediate addition product can be isolated. This is a result of the relatively close balance in resonance stabilization to be regained by elimination (giving an anthracene ring) or addition (resulting in two benzenoid rings). 

The only reported 1,2-addition providing a relatively stable adduct is that of a 1,2-cycloaddition of phthalazinedione to indene (Scheme 40). Compound 162 was isolated and characterized (66JOC3862 71CC695). A similar 1,2-addition reaction to the 9,10-double bond of phenanthrene was also reported but not firmly documented (66JOC3862). 

Although naphthalene, phenanthrene, and anthracene resemble benzene in many respects, they are more reactive than benzene in both substitution and addition reactions. This increased reactivity is expected on theoretical grounds because quantum-mechanical calculations show that the net loss in stabilization energy for the first step in electrophilic substitution or addition decreases progressively from benzene to anthracene therefore the reactivity in substitution and addition reactions should increase from benzene to anthracene. 

Previously, Ohashi and his co-workers reported the photosubstitution of 1,2,4,5-tetracyanobenzene (TCNB) with toluene via the excitation of the charge-transfer complex between TCNB and toluene [409], The formation of substitution product is explained by the proton transfer from the radical cation of toluene to the radical anion of TCNB followed by the radical coupling and the dehydrocyanation. This type of photosubstitution has been well investigated and a variety of examples are reported. Arnold reported the photoreaction of p-dicyanobenzene (p-DCB) with 2,3-dimethyl-2-butene in the presence of phenanthrene in acetonitrile to give l-(4-cyanophenyl)-2,3-dimethyl-2-butene and 3-(4-cyanophenyl)-2,3-dimethyl-l-butene [410,411], The addition of methanol into this reaction system affords a methanol-incorporated product. This photoreaction was named the photo-NO-CAS reaction (photochemical nucleophile-olefin combination, aromatic substitution) by Arnold. However, a large number of nucleophile-incorporated photoreactions have been reported as three-component addition reactions via photoinduced electron transfer [19,40,113,114,201,410-425], Some examples are shown in Scheme 120. 

Because they are not as strongly stabilized as benzene, anthracene and phenanthrene can undergo addition reactions that are more characteristic of their nonaromatic polyene relatives. Anthracene undergoes 1,4-addition at the 9- and 10-positions to give... 

As noted above, the first definition of "aromaticity" was in terms of substitution rather than addition. This is certainly true for many benzene derivatives. However, it must be used with some care since thiophene is by most criteria about as "aromatic" as benzene, but when treated with chlorine or bromine it gives an addition product. The latter is, however, the kinetically controlled product, for when heated or treated with base it loses hydrogen halide and gives the 2-halothiophene.20 Compounds such as anthracene and phenanthrene, which are recognized as having considerable resonance stabilization, also undergo addition reactions. 

In photochemical reactions, some examples have been known of fragmentation of cation radicals of silyl compounds into carbon radicals. Mizuno and colleagues reported a photochemical addition reaction of allylsilane to dicyanophenylethene. Photochemical electron transfer between excited phenanthrene E50 and dicyano-... 

Explain why triphenylene resembles benzene in that it does not undergo addition reactions with Br2, but phenanthrene reacts with Br2 to yield the addition product drawn. (Hint Draw resonance structures for both triphenylene and phenanthrene, and use them to determine how delocalized each iz bond is.)... 

In the presence of secondary amines, 9-cyanophenanthrene undergoes reduction and addition reactions on irradiation to yield 9,10-dihydro-9-cyano-phenanthrene and (63), respectively. The reaction has been studied in considerable detail in order to elucidate the effect of arene structure"" and amine structure " on aminyl and a-aminoalkyl radical formation. It is deduced that in benzene solution diethylamine undergoes exclusive N-H atom transfer to give... 

Formation by a radical addition reaction Wlien phenanthrene and antlrracene are assumed to be formed by the reaction of naphtlialene with a 1,3-butadienylene biradical, tire estimated yield relations would be phenanthrene > anthracene furthermore, a phenantlirene molecule could be formed by the addition of a biphenyl molecule with an acetylene molecule, but an anthracene molecule would not be formed through tire same patliway. These expectations arc in agreement witli tire experimental results. 

Other workers also have applied the Diels-Alder addition reaction to the preparation of angular-substituted derivatives of phenanthrene possibly obtainable as products of degradation of the morphine alkaloids. 

Addition Reactions.- The photoelectron transfer process of the iminium salt (38) with the 3-butenoate anion results in the formation of the allylated product (39). The reaction involves decarboxylation of the 3-butenoate followed by a radical coupling reaction. The photoaddition of halogenated alkenes to the tetraraza phenanthrene (40) yields products (41) of (2+2)-addition. The Eu(III)/Eu(II) photoredox system has been studied with regards to its reactivity toweu ds a-methylstyrene. Irradiation of the system at > 280 nm in methanol yielded the products (42) and(43). ... 

Addition Reactions.- The irradiation through Pyrex of the electron-acceptor alkenes (20) in acetonitrile solution with phenanthrene and hexamethyl disilane brings about a regio-... 

Fused polycyclics also have an increased tendency to undergo addition reaction, which are rare for benzene itself. As a general rule of thumb, additions occur in such a way as to preserve intact benzene rings as much as possible. So, additions to both anthracene and phenanthrene occur at the 9,10 positions, leaving two simple benzene rings intact. 

Both phenanthrene and anthracene have a tendency to undergo addition reactions under the conditions involved in certain electrophilic substitutions. Halogenation and nitration may proceed in part via addition intermediates ... 

Polycyclic aromatic hydrocarbons (PAHs) or polyacenes " like naphthalene, anthracene, phenanthrene etc. are aromatic systems with fused rings (Fig. 5). Since Hiickel s MO theory is mainly developed for monocyclic systems the (An +2)n electrons rule for aromaticity is not directly applicable to PAHs. Number of Clar s k sextet " (benzenoid rings) present in a PAH may give an indication towards its aromaticity. Although sometimes it is termed as superaromaticity (with more than one benzene ring) actually they are not so. Molecules like naphthalene and phenanthrene undergo addition reactions in addition to substitution reactions. The 3D aromatic system " " like fullerene exhibits exclusively addition reactions with hardly any signature of substitution reaction. 

To the organic chemists of the early 1900s and before, an aromatic compound was one that underwent substitution reactions, as opposed to the addition reactions of ordinary alkenes and polyenes. They also noted that if one had fused benzene rings in different arrangements, such compounds were by and large aromatic. Smaller members of this group included naphthalene, anthracene, phenanthrene, and coronene (Structure 4) ... 

Acrylic esters, thioesters and A-acryloyl pyrrole have been identified by Dixon and Rigby as elfective electrophiles in the enantioselective Michael addition reaction with p-keto esters catalysed by a cinchona alkaloid bearing a bulky phenanthrene group (Scheme 1.27). High yields combined with excellent enantioselectivities of up to 96% ee were obtained in almost all cases of substrates. 

The first step in a one-pot formation of a phenanthrene ring system from an enantiomericaUy pure rhenium-bound naphthalene is a TBDMS triflate-promoted Michael addition to 3-penten-2-one (eq 26). Electron-rich rhenium-bound naphthalenes also undergo TBDMS triflate-promoted conjugate addition reactions to less-activated Michael acceptors such as methyl acrylate, leading to the formal Diels-Alder cycloaddition product of naphthalene with this dienophile. ... 

Substituted benzene compounds belong to a class of conjugated compounds called arenes. Examples include benzene, naphthalene, anthracene, and phenanthrene. The common structural feature of arenes is a monocyclic or polycyclic system of k electrons that results in a special stability called aromaticity. As a result, aromatic compounds are much less reactive in electrophilic addition reactions than we would expect based on the reactivity of polyenes. 

In this section we must also mention the syntheses of cyclopentano-phenanthrene derivatives described in Scheme 88. These include, in the first place, attempts to apply the Robinson synthesis (Chapter II, Schemes 24 and 25) to the preparation of tetracyclic products with an angular methyl group at CiQ. By this method, for example, from the acetylmethylcyclo-hexene (63) and 1,5-decalindione (4) it was expected to obtain the diketone (65) through a sequence of Michael addition reactions and intramolecular crotonic condensation. However, it was found that the presence of the ce-methyl group in the acetylcyclene (63) suppressed the Michael reaction and... 

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