1,5-Cyclooctadienes Subject

The mercuration-demercuration reaction of cw,cw-l,5-cyclooctadiene (3) has been widely studied in order to get some insight into the synthesis of 9-oxa and 9-azabicyclo-nonane derivatives. However, the results of the reaction have often been the subject of some controversy since the ratio of the two isomeric bicyclo[3.3.1]- [199 and 201] and [4.2.1]- [198 and 200] nonanes, after reduction (equation 166), strongly depended on the reaction conditions of the mercuration step168,169. 

The selective hydrogenation of 1,5-cyclooctadiene (1,5-COD) and 1,5,9-cyclodode-catriene (1,5,9-CDT), cyclic oligomers of 1,3-butadiene, to the corresponding monoenes has been the subject of considerable interest, since the hydrogenation may constitute one of the steps leading to the synthesis of C8 and C12 lactams, dicarboxylic acids, and their derivatives. 

The bridging chloride ligands in these [Ir(olefin)2Cl]2 compounds are susceptible to metathesis reactions, yielding new dimeric compounds of the form [Ir(olefin)2B]2 where B represents a new bridging ligand. AUcoxides, thiolates, and carboxylates have all been employed successfully in the replacement of chloride. The complexes with B = Br, I have also been prepared, both by metathesis reactions and by direct reaction of cyclooctene or cyclooctadiene with IrBrs or Iris The olefin complexes also provide excellent starting materials for the syntheses of arene and cyclopentadienyl iridium complexes, a subject that will be discussed in the next section. 

Oxidation of [CpCo(CO)2] and [CpCo(CO)(PPh3)] in the presence of PPh3 rapidly produces the radical species [CpCo(CO)(PPh3)] and [CpCo(PPh3)2]. Neither reaction occurs thermally under the conditions used. For reasons outlined previously, these reactions are not subject to electrocatalysis. [Rh(CO)2(j8-diketone)] suffers associative loss of CO in the presence of cyclooctadiene to give [Rh(COD)(j3-diketone)]. ... 

Pyridone photochemistry has been extensively studied because of the important and interesting P-lactam and cyclooctadiene products (see Scheme 2), the dominance of a short-lived singlet excited state in most of the photochemistry, interesting substituent effects, and an absence of solvent effects. A number of reviews have included aspects of pyridone photochemistry - but no comprehensive discussion has been published. The breadth of 2-pyridone photoreactivity stands in contrast to its thermal stability, reluctant partners in Diels-Alder reactions, for example. " The 4-pyridones have provided less useful photochemical reactivity and, consequently, have been the subject of fewer studies. 

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