Question

Would you expect the following reaction to proceed in a conrotatory or
disrotatory manner? Show the stereochemistry of the cyclobutene product, and explain your answer.

Short answer

The reaction happens through disrotatory mode which yields the fused cyclobutene with 2 hydrogen at the ring junction cis to each other.

Step-by-step solution

HOMO photochemical reaction

The two electron pairs in the electrocyclic reaction can be involved. The HOMO for photochemical reaction can be given below.

Bonding is in disrotatory mode

It shows that the bonding is disrotatory mode. Thus, the reaction happens through disrotatory mode which yields the fused cyclobutene with 2 hydrogen at the ring junction cis to each other.

The reaction which involves the diene cyclization ring under photochemical reaction.