Carbocyclic synthesis aromatic compounds

The success of the strategy is further applied for the synthesis of carbo-and spiro-aimulated aromatic compounds [146,147] by the intramolecular cyclization of silyl enolethers to PET-generated arene radical cations. Two types of carbocyclic compounds (170 and 173), varying in ring sizes, may be synthesized [146] starting from the same ketone (i.e., 169), as two types of silyl enol ethers can be produced using either thermodynamic or kinetic enolisation procedures. The core spiro structure (177) of the anticancer antibiotic ffed-ericamycin is also prepared [147] by the PET cyclization of 176 (Scheme 36). 

Among the photochemical reactions of aromatic compounds, the photocycloadditions are most frequently applied to the synthesis of complex polycyclic compounds [6, 9]. The [2+3] or meta photocycloaddition of aromatic compounds and alkenes is the most prominent example [10]. This transformation also demonstrates complementarities between photochemical and ground state reactions since such reactions are almost impossible using conventional activation. A [2+2] ot ortho photocycloaddition between carbocyclic aromatic compounds and alkenes is observed as well. It is often competitive with other cycloaddition modes, in particular the [2+3] mode [11]. Many of these reactions are reversible, and photostationary equilibria are involved. This reaction was much less applied to organic synthesis. Recently, it was found that an acidic reaction medium may have an influence on the outeome of the reaction. The intramolecular photocycloaddition of resorcinol derivatives such as 1 is difficult due to its reversibility (Scheme 29.1). However, in an acidic reaction medium, the cycloadducts 2a,b are protonated at the oxygen atom of the tetrahydrofuran moiety... 

Many 1,2,3-selenadiazoles have been prepared as intermediates for the ultimate preparation of other organic compounds or for biological activity evaluation [6], The most general, extensively applied method is based on the oxidation of semicar-bazones, mostly derived from aromatic and carbocyclic ketones, by selenium dioxide [6, 14, 188-191], Synthesis of 4-(2-naphthyl)-l,2,3-selenazole (117) from semicarbazone (116) is an example (Scheme 36). 

Several other important compounds found in the common aromatic amino acid pathway whose overproduction has been studied are shikimic acid (61) and, to a lesser extent, quinic acid (62) (Scheme 19.41).323 Both 61 and 62 are naturally occurring, highly functionalized carbocyclic rings with asymmetric centers, which can be used as starting material for the synthesis of GS4104 (63), a neuraminidase inhibitor discovered by Gilead Sciences and developed by Roche Pharmaceuticals under the trade name of Tamiflu .324 325 Manipulation of the aromatic amino acid pathway in E. coli has allowed for numerous strains to be assembled that produce both 61 and 62 as well as other intermediates.326 327 As reported by Chandran and co-workers, an E. coli strain has been constructed that synthesized 87 g/L (0.5m) of 61 in 36% (mol/mol) yield with a maximum productivity of 5.2 gL- lr1.328... 

Especially in the case of enaminones bearing a substituent at the nitrogen, side reactions90 become predominant and open a method for synthesis of carbocyclic compounds, which can be aromatized to substituted diphenyl derivatives91. An interesting azocine ring is produced in a side reaction91 (equation 63). 

Because of their aromatic character, pyrones undergo annulation reactions and the introduction of substituents less readily than do most cyclic a,B-unsaturated carbonyl compounds. Nevertheless, some suitable modifications have been developed that allow these compounds to be used effectively in annulation reactions. Some reviews about synthesis of 2-pyrones with 3,4-fused carbocyclic ring systems are currently available (82S337 86G109 92T9111). 

This family of foidamers consists of two, three, or five alternating aromatic heterocydes (pyridazine, pyrimidine, or pyrazine) and methyl-substituted aromatic carbocycles (tolyl, o-xylyl, or m-xylyl) cormected via urea groups (8 Figure 9.3) [14]. In a typical synthesis, heterocyclic diamine compounds were treated with aryl diisocyanate compounds to install a urea linkage between aromatic heterocyde and aromatic carbocyde (Umax = 5). 

A brief summary has appeared on the use of carbohydrate precursors for the synthesis of chiral acyclic, heterocyclic, and carbocyclic compounds. The reaction of monosaccharides (e.g. o-mannose) with benzene or toluene in liquid hydrogen fluoride yielded l,l,2-triaryl-l,2-dideoxyalditols [e.g. (658)] that were further transformed into condensed aromatic hydrocarbons [e.g. (659) and purpuricene (660)]." ... 

Carbopalladation of Arynes by Arylpalladium Complexes Pd-Catalyzed Annulation Reactions of Arynes. Whereas the Pd-catalyzed annulation of alkynes by aiyl halides has proven to be an effective method for the construction of a wide variety of hetero- and carbocycles similar carbopalladation of arynes were unprecedented until Larock and Zhang reported the synthesis of flu-oren-9-ones 115 through the annulation of arynes by o-haloarenecarboxaldehydes (Scheme 12.57) [100]. Larock s group has also developed a Pd-catalyzed annulation of arynes by 2-halobiaryls, affording polycyclic aromatic and hetCToaromatic compounds such as 116 from simple starting materials. Larock and Cheng have independently reported the related double annulation of arynes by simple aryl halides as an efficient route to functionalized triphenylenes (Scheme 12.57) [101]. 

The first five chapters of the Report cover all the possible interconversions between the major functional groups, and Chapter 6 reports specifically on the application of organometallic compounds in synthesis. Two other chapters (Chapters 7 and 8) deal with developments in the synthesis of saturated and partially unsaturated i.e. non-aromatic) carbocyclic and heterocyclic rings, and the final chapter highlights trends and developments in strategy and design of synthesis. A list of reviews on General Synthetic Methods is collected at the end of the Report. 

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