Diels–Alder reaction of maldoxin with an isopropenylallene

The Diels–Alder reaction of maldoxin with an isopropenylallene at 60–75 °C afforded an adduct closely related to chloropestolide A (24%) and a second adduct (0–11%) that underwent an ene reaction to generate the chloropupukeanolide D (11–22%) skeleton. The Diels–Alder reaction occurred with good selectively (>5:1) from a single face of maldoxin under much milder conditions than previously reported for the analogous dimethoxycyclohexadienone. Furthermore, the ene reaction took place under mild conditions, whereas the analogous Diels–Alder adduct from the dimethoxycyclohexadienone did not undergo an ene reaction.