Reaction with aromatic rings

The reactions with aromatic rings were discovered first and are quite interesting. Battersby and Yoewell36 correctly interpreted the structure given earlier as 711 to be the bicyclic isopavine (25). It was later suggested50 that 6 should be the 4-hydroxytetrahydroisoquinoline (8) and that 25 was formed by a nucleophilic attack on the 4-hydroxyl group. Several alkaloids have now been synthesized by this same route.37,71 ... 

Electrophilic aromatic substitution is by far the most common mechanism for reactions with aromatic rings, but in some situations, aromatic rings react with nucleophiles. 

Arylidene-5-oxazolones undergo a ring-opening reaction with aromatic thiols and a second mole of thiol is then incorporated to give products such as 48. ... 

Isopropoxycarbonyloxy radicals undergo facile reaction with aromatic substrates (e.g. toluene) by reversible aromatic substitution. 94 Isopropoxycarbonyloxy radicals react with S to give ring substitution (ca 1%) as well as the expected double bond addition.40 ... 

An application of this reaction to aromatic ring extension is noteworthy. As shown in Eq. 2.43, zirconacydopentadienes couple with diiodobenzene (63) to afford naphthalenes 64. When tetraiodobenzene (65) is used, octasubstituted anthracene derivatives 66 are obtained [7c],... 

In contrast with aliphatic nucleophilic substitution, nucleophilic displacement reactions on aromatic rings are relatively slow and require activation at the point of attack by electron-withdrawing substituents or heteroatoms, in the case of heteroaromatic systems. With non-activated aromatic systems, the reaction generally involves an elimination-addition mechanism. The addition of phase-transfer catalysts generally enhances the rate of these reactions. 

Gierer, J., Yang, E. and Reitberger, T. (1992). The reactions of hydroxyl radicals with aromatic rings in lignins, studied with creosol and 4-methylveratrol. Holzforschung, 46(6), 495-504. 

Sulfonylnitrenes are formed by thermal decomposition of sulfonyl azides. Insertion reactions occur with saturated hydrocarbons.168 169 With aromatic rings, the main products are formally insertion products, but they are believed to be formed through addition intermediates. 

Unsaturated 5(4H)-oxazolones undergo a Friedel-Crafts reaction with aromatic hydrocarbons in the presence of a Lewis acid. In particular, a 2-aryl-4-benzylidene-5(4H)-oxazolone 598 reacts with o- or p-xylene in the presence of aluminum chloride via ring opening and subsequent dearylation to yield 599 as indicated in Scheme 7.191. ... 

For the kinetics and mechanisms of the gas-phase reactions of other 2- to 4-ring PAHs with OH radicals, N03 radicals, and 03, see, e.g., phenanthrene, Kwok et al. (1994a), and indan, indene, fluorene, and 9,10-dihy-droanthracene, Kwok et al. (1997) for dibenzo-thiophene, a volatile S-PAC that is ubiquitous in polluted ambient air environments and forms mutagenic photooxidation products, see Kwok et al. (1999) see also Kwok et al. (1994b) for a review of gas-phase NO-, radical reactions with aromatics. 

Radicals react with aromatic rings by substitution in a manner superficially resembling electrophilic or nucleophilic substitution. The reaction proceeds in... 

Very little work has been done on reactions involving nucleophiles formed from hydrocarbons.124-142 The limitation on basicity of the carbanion, so that it does not react with solvent, has led to use of conjugated hydrocaibons, such as dienes or alkenes conjugated with aromatic rings. When initiated by dissolving alkali metal in liquid ammonia, complex mixtures are often produced on account of reduction processes,124 and regiochemistry and multiplicity of arylation in conjugated systems also create prob-... 

In contrast, the reactions with aromatic ketones are rather complex and hardly predictable. In some cases, only the [2 + 2] cycloadducts were formed, but they isomerized in the dark to the bicyclic [4 + 2] isomers. Thus, mesitylsilene 349 gives with benzophe-none the 2-siloxetane 470, which undergoes spontaneously a ring expansion reaction at room temperature in the dark to give a 1.8 1 mixture of 471 and unchanged 470 (equation 155)235. 

Burgess reagent, (methoxycarbonylsulfamoyl)triethylammonium hydroxide, usually used for the dehydration of secondary or tertiary alcohols, was successfully employed in the formation of cyclic sulfamidates from the corresponding epoxides. It was further shown that the same reaction with aromatic epoxides resulted in the formation of seven-membered ring systems, for example, 57 (Figure 23) <2003SL1247>. 

In summary, intramolecular radical cyclization reactions onto aromatic rings can provide quick access of otherwise not so easily assembled Ca0. -C.ryi bonds, although the yields are generally low and the process suffers from a lack of regioselectivity. Noticeably, Crich found that a catalytic amount of benzeneselenol, which can also be generated in situ reduction of diphenylselenide with stannane [57]. This method should find synthetic utility in intramolecular radical addition to arenes. 

The electron-deficient nature of C60, and its behaviour as an alkene rather than as an aromatic was clearly shown by reaction with ris-Cr)Me5Ru(MeCN)J(CF.jSOa)., a reagent which invariably reacts with aromatic rings, losing all three cyanomethane... 

Trifluoromethyl benzocyclobutenol derivatives 595 undergo ring opening upon treatment with LiTMP followed by reaction with aromatic aldehydes to furnish highly substituted isochroman-l-ols 596 via a laterally-lithiated trifluoromethylketone intermediate (Equation 246, Table 27) <1996SL57>. 

Acid chlorides can be treated with aromatic rings in the presence of a Lewis acid to give aromatic ketones (Following fig.). The reaction involves formation of an acylium ion from the acid chloride, followed by electrophilic substitution of the aromatic ring. 

V-JO Reaction of aromatic rings with ZnCi2, CHjO (formaide-iiydc) and HCI. 

---