Aromatic compounds, fused alkyl

The latter reagent also methylates certain heterocyclic compounds (e.g., quinoline) and certain fused aromatic compounds (e.g., anthracene, phenanthrene). The reactions with the sulfur carbanions are especially useful, since none of these substrates can be methylated by the Friedel-Crafts procedure (11-12). It has been reported that aromatic nitro compounds can also be alkylated, not only with methyl but with other alkyl and substituted alkyl groups as well, in ortho and para positions, by treatment with an alkyllithium compound (or, with lower yields, a Grignard reagent), followed by an oxidizing agent such as Bra or DDQ (P- 1511). 

This reaction is most often carried out with R = aryl, so the net result is the same as in 14-17, though the reagent is different. It is used less often than 14-17, but the scope is similar. When R = alkyl, the scope is more limited. Only certain aromatic compounds, particularly benzene rings with two or more nitro groups, and fused ring systems, can be alkylated by this procedure. 1,4-Quinones can be alkylated with diacyl peroxides or with lead tetraacetate (methylation occurs with this reagent). 

The six points of the hexagon represent the six carbon atoms, with the hydrogen atoms omitted for simplicity. The circle represents the de-localized tt electrons, which are spread out evenly over the ring. The molecules of other aromatic compounds contain benzene rings with various side groups or two (or more) benzene rings linked by alkyl chains or fused side by side, as in naphthalene (CioHg) ... 

The Catellani s alkylation-alkenylation sequence using norbomene offers a useful synthetic method for 2,6-dialkylated 1-substituted benzenes. Lautens applied the reaction to the synthesis of fused aromatic compounds using ort/jo-substituted iodobenzenes and bromoalkenes. Reaction of o-iodotoluene (11) with ethyl 6-bromo-2-hexenoate (13) afforded the benzocarbocycle 14 via monoalkylation and intramolecular Heck reaction. It is important to use tri-2-furylphosphine (1-3) as a ligand [4]. Similarly the 2,5-disubstituted 4-benzoxepine 17 was obtained in 72% yield by the reaetion of 1-iodonaphthalene (15) with the unsaturated bromo ester 16 [5]. 

Kantlehner et reported the formylation of (hetero)aromatic compounds including unsubstituted and alkyl-substituted aromatics, aromatic ethers, tertiary aromatic amines, fused aromatic rings and thiophenes using new formylating agents (Scheme 1.1) based on formamide derivatives in the presence of Lewis acids. 

Fused aromatic compounds such as polyacenes have attracted much attention as organic conductive materials. However, established methods are very limited. Lack of general and convenient synthetic methods for fused aromatic compounds and their very poor solubility in organic solvents are the most serious problems that control further advances in this very important field. Taka-hashi and coworkers have recently developed a synthetically useful method for preparation of fused aromatic compounds, by using the zirconocene-mediated aromatization of alkynes. In order to solve the solubility problem, alkyl substituents are introduced into to the skeletons. In principle, two types of synthetic protocols have been used. Type I protocol is via the homologation starting from a functionalized benzene derivative (Scheme 3) [75] the Type II protocol is via the intermolecular cycloaddition of two alkynes to an arene (Scheme 4) [76]. 

Fused pyrazole compounds have been prepared from A-alkyl substituted pyrazoles. For example, a palladium-catalyzed/norbornene-mediated sequential coupling reaction involving an aromatic sp2 C-H functionalization as the key step has been described, in which an alkyl-aryl bond and an aryl-heteroaryl bond were formed in one pot <060L2043>. A variety of highly substituted six-membered annulated pyrazoles 59 were synthesized in a one-step process in moderate yields from IV-bromoalkyl pyrazoles 57 and aryl iodides 58. 

The fact that most alkylated benzenes show the same tendency to soot is also consistent with a mechanism that requires the presence of phenyl radicals, concentrations of acetylene that arise from the pyrolysis of the ring, and the formation of a fused-ring structure. As mentioned, acetylene is a major pyrolysis product of benzene and all alkylated aromatics. The observation that 1-methylnaphthalene is one of the most prolific sooting compounds is likely explained by the immediate presence of the naphthalene radical during pyrolysis (see Fig. 8.23). 

Thiophene sulfones show no aromatic character, they behave as dienes and also show reactions of compounds containing a C = C bond conjugated with an electron-withdrawing group. Thiophene sulfone itself is highly unstable, but alkyl and aryl groups and fused benzene rings increase the stability. 

Oxidations of alkylated fluoroaromatic compounds arc mostly applied in the syntheses of the corresponding aromatic mono-, di- and tricarboxylic acids. The reactions in this section also include aromatization (i.e., dehydrogenation) of polyhydroaromatic compounds and epoxi-dation of unsaturated benzo-fused bicyclic compounds. 

The photolysis of nitrosopregnone steroid (117) afforded the 18,20-benzo-fused compound (118) as the major product (24%) along with the diol (119) (6%), whilst the expected C(18) rearranged product (120) is not isolated (Scheme 17).277 Reaction proceeds via the C(18) alkyl radical (121), formed in accordance with the accepted C(ll) O—NO bond homolysis and H-abstraction pathway, before either addition of C(11) radical (121) to the aromatic ring to afford (118) or H abstraction to give (119). 

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