Complex fused ring systems

The term polycyclic pigments refers to pigments which are derived from the an-thraquinone skeleton, either by chemical structure or by synthesis. The complex fused-ring systems which are discussed in this context are all at least remotely related to the parent anthraquinone structure. 

A further addition-cyclization process that leads to complex fused-ring systems is the dicobalt octacarbonyl-mediated Pauson-Khand reaction which, applied to enynes 209 and 211, gives respectively and in modest yields the tricyclic cyclopentenones 210215 and 212.216... 

When the enediyne substrate has functional groups that can trap the initially formed Bergman diradical, the rapid construction of complex fused ring systems becomes feasible. J.E. Anthony and co-workers prepared an acenaphthene derivative as well as a substituted perylene using this concept. " ... 

Several elegant examples of a double Michael addition sequence (inter-molecular followed by intramolecular) leading to complex fused-ring systems have been published this year (Scheme and Ghatak et al. ° describe... 

Cholesterol is a principal component of animal cell plasma membranes, and much smaller amounts of cholesterol are found in the membranes of intracellular organelles. The relatively rigid fused ring system of cholesterol and the weakly polar alcohol group at the C-3 position have important consequences for the properties of plasma membranes. Cholesterol is also a component of lipoprotein complexes in the blood, and it is one of the constituents oiplaques that form on arterial walls in atherosclerosis. 

In addition, these fused-ring systems allow a one-step syntheses of mixed arene-dienyl complexes (136) ... 

Photolysis of 2-substituted cyclopropyl carbyne complexes afforded 4-substituted cyclopentenones (equation 115). Irradiation of the diastereomeric mixture of either cis- or /ra j,-2,3-dimethylcyclopropyl carbyne complexes gave selectively the irons-3,4-dimethylcyclopentenone, indicating a rapid cyclopropane photoisomerization prior to photooxidation (equation 116). The cis configuration is, however, retained in fused ring systems. Thus photooxidation of bicyclo[4.1.0]hept-7-yl carbyne complex results in... 

Annulation of furans via electrochemical oxidation at the anode has become an important process for the synthesis of complex polycycles, and was covered in a review <2000T9527>. Furans tethered at the 3-position to electron-rich alkenes, enol ethers, or vinyl sulfides were converted to [6,5] and [7,5]-fused ring systems <1996JOC1578, 2002OL3763, 2004JOG3726, 2005JA8034>, as illustrated in Scheme 20. Analysis of crude reaction mixtures and side... 

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