Seven-membered, Medium, and Large Rings

The arene-olefin cycloaddition has been used in a synthesis of the 

Diels-Alder reaction and ozonolysis of the product (67) leads to a 

An important achievement is the synthesis of optically active fusicoccane, in which the key reaction is cyclization of the bis aldehyde (69). 118 Ring closure of the cobalt complex propargyl derivative (70), involving reaction via a cobalt stabilized carbocation gives access to eight-membered rings117 which are also the product of the nickel(0) catalysed [4+4]cycloaddition of the tetraene (71).118 

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