Chiral squaramides as highly enantioselective catalysts for michael addition reacions of 4-hydroxycoumarins and 4-hydroxypyrone to β,γunsaturated α-keto esters

摘要

(Figure Presented) Distance brings forth beauty: The first highly enantioselective organocatalytic Michael addition of 4-hydroxycoumarins and the analogous 4-hydroxy-6methyl-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).