Inverting the reactivity of troponoid systems in enantioselective higher-order cycloaddition.

By the replacement of the oxygen with the sulfur atom in tropone, a novel reactivity pattern of troponoid systems in enantioselective transformation was achieved. It utilizes tropothione as an 8π-component in the [8+2]-cycloaddition involving α,β-unsaturated aldehydes. The stereochemistry of the process is governed through the aminocatalytic LUMO-activation of the carbonyl reactant. It is in marked contrast to recently developed aminocatalytic higher-order cycloadditions proceeding via HOMO-activation strategies.