Activation of the Dienophilicity of Indoles in Normal Electron Demand [4 + 2] Cycloadditions under High Pressure

[reaction: see Text] Activation by either high pressure or a combination of Lewis acid catalysis and high pressure allows indole derivatives to behave as dienophiles in [4 + 2] cycloaddition reactions under mild conditions. The biactivation mode has the highest impact on the stereoselectivity of the reaction. The cycloadducts resulting from these reactions are characterized by boat-shape conformations that bear well-defined orthogonal planes.