Application of β-Keto Acylpyrazoles as 2C Synthons in Asymmetric Cyclizations of -Hydroxychalcones: Stereoselective Construction of -3,4-Dihydrocoumarins.

An asymmetric tandem esterification/Michael addition reaction of β-keto acylpyrazoles with -hydroxychalcones has been established under the catalysis of a bifunctional squaramide-tertiary amine. A wide variety of biorelevant 3,4-dihydrocoumarin derivatives were generally obtained in high yields (up to 93%) with excellent diastereo- and enantioselectivities (>19:1 dr, up to 93% ee) under mild reaction conditions. This reaction represents the successful application of β-keto acylpyrazoles as 2C building blocks in catalytic asymmetric cyclizations.