Chiral Squaramides as Highly Enantioselective Catalysts for Michael Addition Reactions of 4‐Hydroxycoumarins and 4‐Hydroxypyrone to β,γ‐Unsaturated α‐Keto Esters

Abstract

Distance brings forth beauty: The first highly enantioselective organocatalytic Michael addition of 4-hydroxycoumarins and the analogous 4-hydroxy-6-methyl-2-pyrone to β,γ-unsaturated α-keto esters by using chiral squaramides as the organocatalysts is disclosed. The efficiency of the process is attributed to the hydrogen-bonding activation (see scheme). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.