Why a proximity-induced Diels-Alder reaction is so fast.

Unlike normal Diels-Alder reactions of acyclic alkadienes with alkenes, the vinylbicyclo[2.2.2]octene employed in the Baran total synthesis of vinigrol undergoes a quantitative Diels-Alder reaction with a tethered alkene at room temperature. Density functional theory calculations reveal that this unprecedented reactivity originates from a combination of preorganization, diene strain, and tether stabilization.