Application of β‑Keto\nAcylpyrazoles as\n2C Synthons in Asymmetric Cyclizations of <i>ortho</i>-Hydroxychalcones:\nStereoselective Construction of <i>trans</i>-3,4-Dihydrocoumarins

An\nasymmetric tandem esterification/Michael addition reaction of\nβ-keto acylpyrazoles with <i>o</i>-hydroxychalcones\nhas been established under the catalysis of a bifunctional squaramide-tertiary\namine. A wide variety of biorelevant 3,4-dihydrocoumarin derivatives\nwere generally obtained in high yields (up to 93%) with excellent\ndiastereo- and enantioselectivities (>19:1 dr, up to 93% ee) under\nmild reaction conditions. This reaction represents the successful\napplication of β-keto acylpyrazoles as 2C building blocks in\ncatalytic asymmetric cyclizations.