Reactivity Enhancement of Noncovalent Catalysts by Molecular Iodine

Thioureas and related noncovalent catalysts constitute a key pillar of stereoselective catalysis, yet their practical utility is often limited by high catalyst loadings or modest reactivity. Here we introduce a simple and broadly applicable strategy to enhance both the activity and selectivity of these catalysts through the addition of small amounts of molecular iodine (typically 10 mol% relative to the organocatalyst). The concept is effective across multiple classes of organic reactions and applies to hydrogen-bond, halogen-bond, and chalcogen-bond donors alike. Mechanistic and computational studies support the formation of an iodine-thiourea complex as the catalytically active species, providing a coherent rationale for the observed rate and selectivity enhancements.