The diene lactone shown in part (a) has one electron-donating group and one electron-wi...

The diene lactone shown in part (a) has one electron-donating group and one electron-withdrawing group .This diene lactone is sufficiently electron-rich to serve as the diene in a Diels–Alder reaction. (a) What product would you expect to form when this diene reacts with methyl acetylenecarboxylate, a strong

dienophile?

(b) The Diels–Alder product A is not very stable. Upon mild heating, it reacts to produce CO2 gas and methyl benzoate (PhCOOCH₃), a very stable product. Explain how this strongly exothermic decarboxylation takes place. (Hint: Under the right conditions, the Diels–Alder reaction can be reversible.)