I was looking at the synthesis of corallopyronin A in the following paper by Rentsch and Kalesse: Angew. Chem. Int. Ed. 2012, 51 (45), 11381–11384.
There is one reaction which is described as
oxidation and a retro Diels–Alder reaction generated pyrone
I understand that the DMP oxidises the secondary alcohol to a ketone, and at the end there is an intramolecular esterification to produce the lactone, but I don't quite understand how the retro Diels–Alder reaction works. Could someone explain the reaction steps?