Asymmetric Formal [4 + 2] Annulation of o‑Quinone Methides with β‑Keto Acylpyrazoles: A General Approach to Optically Active trans-3,4-Dihydrocoumarins

An asymmetric cascade reaction between β-keto acylpyrazoles and o-quinone methides in a formal [4 + 2] fashion to access potentially pharmacological active trans-3,4-dihydrocoumarins has been achieved efficiently by using a quinine-based chiral squaramide as the catalyst. The desired products were obtained in high yields with excellent diastereo- and enantioselectivities (up to 96% yield, >19/1 dr and 96% ee) under mild reaction conditions.以基于奎宁的手性方酰胺为催化剂，可高效实现β-酮酰基吡唑与邻醌甲基化物之间以形式[4+2]环加成模式进行的不对称级联反应，从而获得具有潜在药理活性的反式-3,4-二氢香豆素类化合物。在温和反应条件下，目标产物可获得高收率以及优异的非对映选择性和对映选择性，产率最高达96%，非对映选择性比例>19/1，对映体过量值为96%。