Bicyclo octatriene complexes

Fig. 15 [4+2] Cycloaddition reactions of r -anisole complexes via a 4H-anisolium intermediate and the formation of various bicyclo[2.2.2]octadiene and bicyclo[2.2.2.]octatriene complexes...

Thermal rearrangement of the iron tetracarbonyl complex of syn-tricyclo-[4,2,0,0 ]octa-3,7-diene to a bicyclo[4,2,0]octatriene complex is believed to proceed by loss of CO followed by a concerted disrotatory ring-opening (Scheme 59) in which the metal plays an important role in overcoming the forbidden nature of... 

The more activated TpRe(CO)(MeIm)(q -anisole) complex has demonstrated a slightly broader range of cycloaddition reactivity. The anisole complex 110 cychzes with DM AD to give the diastereomeric bound bicyclo [2.2.2] octatriene 111 isolated as a 1 1 ratio of coordination diastereomers (Fig. 23). Oxidation of these complexes liberates the corresponding triene 112 as well as the disubstitut-ed anisole 113, which presumably is generated with acetylene from the cycloreversion of 112. 

Dicyclopentadiene has two cyclopentene rings with different reactivities. In the reaction with nickel complexes and carbon dioxide only the more reactive norbornene ring couples with CO2, whereas the unstrained ring proved to be unreactive [14,16]. The last example in Figure 6 is cyclooctatetraene, which stands in a temperature-dependent equilibrium with bicyclo[4.2.0]octatriene. Both isomers undergo an oxidative coupling with nickel and CO2. Decomposition by hydrochloric acid leads to cycloocta-2,4,6-triene-carboxylic acid and bicyclo-[4.2.0]octa-2,4-diene-7-carboxylic acid [14]. 

---