The following two molecules can undergo a thermally allowed cycloaddition reaction. Show the reaction, and explain why it is allowed.

Diagram showing molecular orbitals and thermal cycloaddition reaction with products below.

Diagram of molecular orbitals and thermal cycloaddition reaction with different products below.

Diagram of molecular orbitals and thermal cycloaddition reaction with products below, showing structural changes.

Diagram of molecular orbitals and thermal cycloaddition reaction with products below, highlighting structural changes.