Subscribe to RSS
DOI: 10.1055/s-0034-1378950
Highly Enantioselective Route to Chromenes
Brønsted Acid Catalyzed, Conjugate Addition of β-Dicarbonyls to In Situ Generated ortho-Quinone Methides–Enantioselective Synthesis of 4-Aryl-4H-Chromenes.
Angew. Chem. Int. Ed. 2014;
53: 7923-7927
Publication History
Publication Date:
18 August 2014 (online)
Significance
An asymmetric synthesis of chromenes 3 is reported by the Schneider group. The reaction is catalyzed by phosphoric acid catalyst A and couples ortho-hydroxy benzhydryl alcohols 1 with various β-dicarbonyl compounds 2. The proposed reaction mechanism relies on a dual role of the chiral catalyst. It initially promotes the dehydration of the alcohol delivering the reacting ortho-quinone methides and subsequently catalyzes the asymmetric Michael addition. The final cyclization step is successfully achieved by the in situ addition of a stronger achiral acid (PTSA).
#
Comment
Because the chromene motif is an important framework in natural products and pharmacologically active molecules, the development of asymmetric routes for its preparation is of high interest. The authors describe an operationally simple organocatalytic strategy which delivers the desired products in good yield and in good to excellent enantioselectivity. The remarkably wide scope of the transformation, which allowed the authors to generate a library of differently substituted compounds, further underlines the synthetic usefulness of such an approach.
#
#