The first Diels–Alder reaction of vinyl arenes with ene systems catalyzed by MOFs is reported. Maleimides and maleic anhydride were annulated/dehydrogenated on styrenes in the presence of a mixed-metal (FeNi)MIL-88A catalyst. Neither an additional oxidant nor a source of halogen is needed to drive this oxidative [4 + 2] cyclization reaction. Kinetic evidence such as activation entropy corroborates the proposed concerted mechanism. The reaction proceeds merely through a cost-effective catalyst in water as the greenest solvent. The product of annulation of styrene with maleic anhydride was used for the first L-selective annulative π-extension on naphthalene.