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Diels-Alder reaction was discovered by the German chemists Otto Diels and Kurt-Alder in 1928. Diels-Alder reaction is an important organic reaction which includes a substituted alkene in the form of a dienophile and a conjugated diene. It proceeds via concerted mechanism. Diels alder reaction can be used to generate 6 membered rings since there is a simultaneous construction of two new Carbon-carbon bonds.

Diene is an organic compound which comprises of two conjugated pi bonds (4 pi bonds) while dienophile is a diene loving compound containing 2 pi electrons. When the interaction between them, occurs a transition state without any additional energy barrier, is obtained.

Here in the question given, pyrone is the diene

while the alkyne is dienophile.

First of all, the Diels-Alder reaction of given diene and dienophile generates a product in which double bonds are not conjugated.

Diels-Alder reaction

so a more stable product can be formed by the loss of on heating.