Carbocyclic compounds ring strain

The degradation of xanthone by Arthrobacter sp. strain GFBIOO closely resembled the pathways used for carbocyclic compounds. In a yeast-supplemented medium, initial dioxygenation to the 3,4-dihydrodiol was followed by dehydrogenation to 3,4-dihydroxyxanthone and extradiol ring fission to a coumarin and subsequent production of 2,5-dihydroxybenzoate (Figure 10.38) (Chen and Tomasek 1991 Tomasek and Crawford 1986). 

A sequence of an inter- and an intramolecular Heck coupling has been used to construct the 26-membered carbocyclic compound 60 from an acyclic precursor 59, which presents half of the target molecule (Scheme 20). The first step of this twofold coupling is favored to occur inter- rather than intramolecularly, because the latter would lead to a highly strained 13-membered ring system with a biaryl unit and a frans-configmed double bond. In the cyclizing second step, polymerization is disfavored by the orientation of the two side arms in the 3- and 3 -positions of the initially formed 1,1 -biaryl derivative. 

Sh2 and Sh2 reactions have been devised to prepare sulfides or sulfones. The former ones are limited to highly strained carbocyclic compounds [6d-e, 76]. The latter ones are more common, and various vinylic or allylic derivatives including stan-nanes and cobaloximes are known to react with sulfur-centered radicals [77]. A representative example is shown in Eq. (32), where the three-membered ring in IH-cyclopropabenzene opens upon attack by various thiyl radicals to give the corresponding ort/zo-substituted toluenes. 

This chapter deals with the names, physical properties, structural features, and conformational characteristics of the cycloalkanes. Because of their cyclic nature, members of this class of compounds can exhibit new types of strain, such as ring strain and transannular interactions. We end with the biochemical significance of selected carbocycles and their derivatives, including steroids. 

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... 

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