Additions to Benzene

Additions to Benzene.—Stereoselectivity in 1,2-, 1,3-, and 1,4-photoadditions to benzene has been surveyed. Irradiation of benzene and cis-cyclo-octene with a low-pressure mercury arc gives both the exo- and endo-1,3-adducts (473) and a single 

2- adduct which was selectively converted into a maleimide adduct shown by X-ray analysis to be (474). The 1,2-adduct is therefore endo, in accord with the theory of endo-benzene-alkene association in the ground state of the reactants.  

A number of methylenebicyclo[3,2,l]octadienes (509) have been prepared and shown to rearrange to the tetracycloalkenes (511) [presumably via thermal cycloaddition of initially produced allenes (510)] in a manner directly analogous to the known rearrangement of bicyclo-octadienones with the same bonding system. However, (509 = Me, = H) gives three products, (511 R = H), (513), and (514). 

Irradiation of triptycene (531) gives only the isomer (533). This behaviour should be compared with that of barrelene and its mono- and dibenzo-derivatives which undergo di-7i-methane rearrangements, which in the case of (531) would be expected to give (532). It has been suggested that the formation of (533) involves a 1,5-sigmatropic 

Photolysis of 4-methylverbenene (542), however, gives 3-methylenelimonene (543), and a biradical intermediate analogous to (541) is suggested.  

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In addition to benzene and naphthalene derivatives, heteroaromatic compounds such as ferrocene[232, furan, thiophene, selenophene[233,234], and cyclobutadiene iron carbonyl complexpSS] react with alkenes to give vinyl heterocydes. The ease of the reaction of styrene with sub.stituted benzenes to give stilbene derivatives 260 increases in the order benzene < naphthalene < ferrocene < furan. The effect of substituents in this reaction is similar to that in the electrophilic aromatic substitution reactions[236]. 

The antineoplastic agent mitindomide (160) in fact represents the well-known product from irradiation of maleimide in benzene [30]. The activity of this old compound was uncovered by one of the large antitumor screens maintained by the National Cancer Institute, The structure is sufficiently complex and the starting materials sufficiently available to lead one to suspect that the product is still produced photochemically. The product can be rationalized by assuming successive 1,4 and 1,2 additions to benzene. Intermediate 159a involves the 1,4 followed by 1,2 addition intermediate 159b presupposes the steps occur in the reverse order. 

The products consistently exhibit retention of the original olefin stereochemistry and are probably formed in a concerted manner. An exciplex formed from singlet excited benzene and the ground state olefin (allowing relaxation of the orbital symmetry requirements for concerted 1,3- and 1,4-cycloaddition) has been proposed to account for these products/126 Srinivasan and Hill reported an unusual photochemical addition to benzene to form cycloadduct (52)<74) ... 

Intramolecular amine addition to benzene has been reported in the phenyl-alkylamines 368 to give the meta adducts 369 in low yield,306 whereas the [co-(anilino)alkoxy]nitrobenzenes 370 undergo photocyclization in acetonitrile to give heterocycles 371.307... 

In addition to benzene and alkylbenzenes several other aromatics (nitrobenzene, aniline, anisole, benzoic acid, etc.) were hydrogenated, usually with much lower rates. Benzoic acid and benzoates gave the corresponding cyclohexyl derivatives, however, in case of acetophenone some deoxygenation was also observed with the Ru-3 catalyst [158]. This latter observation raises some doubts regarding the truly homogeneous nature of the reaction. 

In addition to benzene compounds, pyridine, thiophene, furan and naphthalene sulfonylureas are also active. Compounds with the unmodified sulfonylurea bridge are generally more active than compounds with substituted bridging groups. Compounds with the bridges shown in Figure 14 have shown some activity. 

Linear alkylbenzenes are made from -paraffms (Cio-Cu) by either partial dehydrogenation to olefins and addition to benzene with HF as catalyst (60%) or chlorination of the paraffins and Friedel-Crafts reaction with benzene and an aluminum chloride catalyst (40%). See Chapter 24 for more information. 

Diazomethyl)-1,4-diphenyl-1,2,3-triazole (354) reacts with 1,4-disubstituted benzenes or naphthalenes to give a mixture of carbene derived norcaradiene/cycloheptatriene products (355) and (356) (Scheme 68). Attack is favored adjacent to the more highly branched substituent. When R = = Pr, a mixture of triazole derivatives (357) and (358), formed by addition to benzene and... 

Another reactive carbonyl compound is formaldehyde. Draw out the first step of its addition to benzene in acid solution. 

In connection with reactions where a solvent is required, it must be noted that all transformations promoted by chiral Mo catalysts may be carried out in toluene (in addition to benzene) or various alkanes (e.g., n-pentane) with equal efficiency (see below for specific examples). Moreover, although 5 mol % catalyst is typically used in our studies, 1-2 mol % loading often delivers equally efficient and selective transformations. 

Good yields of addition to benzene and its derivatives have also been reported under both thermal and photochemical conditions [202,203],... 

Bradshaw [74] reported in 1966 that maleimide undergoes sensitized photochemical addition to benzene, producing the imide analog of the corresponding maleic anhydride photoadduct. The author observed that the reaction probably proceeds by the addition of electronically excited maleimide to benzene. The photoaddition proved successful also with toluene, /-butylbenzene, and ethylbenzene. Simultaneously, Bryce-Smith and Hems [75] reported that 2 1 photoadducts are formed from maleimide, iV-n-butyl-,. V-benzyl-, iV-o-tolyl-, and iV-2,6-xylylmaleimide with benzene.. V-Phenyl, N-p-tolyl-, and A-p-methoxyphenylmaleimide did not form photoadducts. Trifluoroacetic acid was found to be virtually without effect on the photoaddition of N-n - bulyI maleimide No phenyl-A- -butylsuccinimide was detected [36], It was concluded that a dipolar intermediate is not involved. When N-n-bulylmalcimide and benzene were irradiated in the presence of tetra-cyanoethylene, a 1 1 1 adduct was formed [37],... 

On the basis of these observations, Bryce-Smith et al. [115] introduced a rule stating that for addition to benzene, Pmeta when 9.6 eV < IP (alkene) <8.65 eV. They concluded that if this rule is correct, ortho addition of ethylenes to Si benzene necessarily involves an element of charge transfer to or from the ethylene. Indeed, a marked effect of polar solvents (methanol or acetonitrile) in promoting the ortho addition of benzene to ethyl vinyl ether and tetramethylethene was observed (portho increased by 20-50%, whereas cpmeta was unaffected. One exception to this rule was found by Heine and Hartmann [10], who discovered that vinylene carbonate (IP = 10.08 eV) undergoes mainly meta photocycloaddition to benzene, accompanied by some para addition. Bryce-Smith and Gilbert [46] commented that their rule referred to quantum yields and not chemical yields, whereas no quantum yields were given for the vinylene carbonate additions. Moreover, quantum yield measurements should be made at low conversions because most ortho cycloadducts are photolabile. 

In addition to benzene rings, cycloheptatriene is activated or protected by forming the stable if complex 300. An example of the strong stabilization effected by coordination is shown by isolation of the optically active l,3,5-cycloheptatrien-3-ols 301, 304 and 305 as their enol forms. l,3,5-Cycloheptatrien-3-ol was isolated as complex 301 by hydrolysis of silyl enol ether 300. The triene system is stabilized by coordination,... 

The reaction of ozone with benzene and phenol was studied for the first time by ab initio methods <2003PCA7574>. The addition to benzene had the largest calculated activation energy (15.8 kcal mol the experimental value is... 

A number of by-products may be isolated from sodium stannite reductions. In addition to benzene, aniline gives phenol, azobenzene, phenyl azide, and phenylhydrazine.107 10 108 109 The danger of hydrolytic cleavage in alkaline media, previously discussed in connection with the... 

The small amount of naphthylbiphenyl probably forms from an addition to benzene and insertion in biphenyl. 

Tomat R, Yecchi E. Electrocatalytic production of OH radicals and their oxidative addition to benzene. J Appl Electrochem 1971 1 185-188. 

Case studies involving individuals who were previously chronically exposed to benzene report significant chromosomal aberrations in bone marrow and lymphocytes (Fomi and Moreo 1967, 1969 Hartwich et al. 1969 Major et al. 1992 Picciano 1979 Sellyei and Kelemen 1971 Tough and Court-Brown 1965 Tough et al. 1970 Van den Berghe et al. 1979 Yardley-Jones et al. 1990). Other mutagens in addition to benzene may have been involved since most of the workers were occupationally exposed to more than one chemical. 

Insertion reactions [81], alkene additions [82] and even additions to benzene and hexafluorobenzene [83] have been observed using these sources of carbenes, as shown in Figure 6.53. 

The outstanding dienophilicity of benzynes is highlighted by their Diels-Alder additions to benzenes. Tetrachlorobenzyne (520), easily generated by lithiation of hexachlorobenzene (519), smoothly reacted with benzene to afford tetrachlorobenzobarrelene (521) in -60% yield (Scheme 122). The parent benzyne (478) underwent similar addition to benzene, although not so efficiently. ... 

Many compounds in addition to benzene are aromatic. Several examples are presented in Section 17.8. 

In addition to benzene and its derivatives, there exist other aromatic hydrocarbons, containing two or more rings of carbon atoms. Naphthalene, CioHg, is a solid substance with a characteristic odor it is used as a constituent of moth balls, and in the manufacture of dyes and otlier organic compounds. Anthracene, and phenanthrene,... 

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