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Asymmetric oxa‐Michael‐aza‐Henry Cascade Reaction of 2‐Hydroxyaryl‐Substituted α‐Amido Sulfones and Nitroolefins Mediated by Chiral Squaramides
Author(s) -
Zheng Bo,
Hou Wenduan,
Peng Yungui
Publication year - 2014
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201402236
Subject(s) - squaramide , acetophenone , diastereomer , chemistry , yield (engineering) , michael reaction , catalysis , enantiomer , organocatalysis , organic chemistry , enantiomeric excess , enantioselective synthesis , medicinal chemistry , materials science , metallurgy
Abstract A series of chiral squaramides were employed in the oxa‐Michael‐aza‐Henry cascade reaction of 2‐hydroxyaryl‐substituted α‐amido sulfones and nitroolefins. In the presence of 10 mol % of a squaramide catalyst and K 2 CO 3 (aq) in CHCl 3 at 0 °C, this reaction proceeded smoothly to afford chiral multisubstituted 4‐amino‐3‐nitrobenzopyrans, bearing a readily removable N‐Boc protecting group (Boc= tert ‐butoxycarbonyl), in excellent yields (up to 98 %) and enantioselectivity [up to 98:2 enantiomeric ratio ( er ) and 93:7 diastereomeric ratio ( dr )]. The 4‐amino‐3‐nitrobenzopyrans were converted into chiral 3,4‐diamino chromanes, which were further exploited as chiral ligands in the asymmetric transfer hydrogenation of acetophenone, providing 1‐phenylethanol in up to 84 % yield and 93.5:6.5 er .