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The electrocyclic reaction of a polyene, which results in a closed (ring) system, is referred to as the thermal electrocyclic ring closure reaction.

The polyenes having an odd number of pi electrons undergo disrotation, and the ones having an even number undergo conrotation in an electrocyclic reaction.

Step 2: Thermal electrocyclic ring closure of a

The decatetraene consists of an even number of pi bonds and hence, will undergo conrotation under thermal conditions.

The electrocyclic ring closure of the given decatetraene under thermal conditions yields a trans product.

Thermal electrocyclic ring closure of a

The electrocyclic ring closure of the given decatetraene under thermal conditions yields a cis product.

Thermal electrocyclic ring closure of b