Optically Active 3,4-Dihydrocoumarins via Organocatalyzed Asymmetric [4+2] Annulation of ortho-Hydroxyl Functionalized p-Quinone Methides with β-Keto Acylpyrazoles

An organocatalyzed asymmetric formal [4+2] annulation of ortho-hydroxyl functionalized p-quinone methides with beta-keto acylpyrazoles has been developed, which provides an efficient approach to access optically active 3,4-dihydrocoumarins. Under the catalysis of a quinine-derived bifunctional squramide, the reactions of a wide range of ortho-hydroxy-phenyl substituted p-quinone methides and beta-keto acylpyrazoles took place smoothly to generate the corresponding polysubstituted 3,4-dihydrocoumarins in good yields with high levels of diastereo- and enantio-selectivities (up to 96% yield, >19/1 dr and 98% ee) under mild reaction conditions.

Automated summary

An organocatalyzed asymmetric formal [4+2] annulation of ortho-hydroxyl functionalized p-quinone methides with beta-keto acylpyrazoles has been developed, providing an efficient approach to access optically active 3,4-dihydrocoumarins. The reactions demonstrate good yields, high levels of diastereo- and enantio-selectivities under mild reaction conditions.