The following transformation involves a series of

Concept:

Cycloaddition Reaction:

• The cycloaddition reaction is a chemical reaction in which two or more unsaturated molecules combine with each other to form a cyclic compound, with a reduction of bond multiplicity.
• In other words, cycloaddition reaction indicates the addition of two or more π-bonds to form a cyclic adduct with the formation of bonds at the end of the pi bonds.

Explanation: 

• The reaction is a [4+2]π cycloaddition reaction followed by a cycloreversion reaction, in which 5-oxo-3-phenyl-4,5-dihydro-1,2,3-oxadiazol-3-ium-4-ide acts as a dipolarophile. whereas the (1Z,5Z)-cycloocta-1,5-diene acts as a dienophile. The dipolarophile reacts in a cycloaddition reaction with 1,3-dipoles.

• The reaction proceeds through the following mechanism

Conclusion:

Hence, the following transformation involves a series of ​​cycloaddition and cycloreversion reactions.