Diastereodivergent and Enantioselective Organocatalytic Synthesis of Spiro-Fused Coumarins via [4+2] Cycloadditions

A highly enantioselective, organocatalytic, diastereodivergent synthesis of spiro-fused coumarin derivatives via trienamine-mediated Diels-Alder reactions with cyclic 2,5-dienones is reported. Using a cinchonidine-based primary amine and either <i>p</i>-methylbenzoic acid or triethylamine enables reversible diastereoselectivity, providing complementary enantioenriched diastereoisomers. The influence of electron-withdrawing groups at C3 of coumarins is delineated, revealing distinct reactivity patterns. Computational studies provide insight into the mechanism and additive-controlled diastereodivergence.