Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 18, Issue 21, Pages 6679-6687Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201103293
Keywords
butendiones; conjugate addition; organocatalysis; oxindoles; Paal-Knorr cyclization
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Funding
- National Natural Science Foundation of China [20802074]
- National Basic Research Program of China (973 Program) [2010CB833300]
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An asymmetric conjugate addition of 3-monosubstituted oxindoles to a range of (E)-1,4-diaryl-2-buten-1,4-diones, catalyzed by commercially available cinchonine, is described. This organocatalytic asymmetric reaction affords a broad range of 3,3'-disubstituted oxindoles that contain a 1,4-dicarbonyl moiety and vicinal quaternary and tertiary stereogenic centers in high-to-excellent yields (up to 98?%), with excellent diastereomeric and moderate-to-high enantiomeric ratios (up to 99:1 and 95:5, respectively). Subsequently, cyclization of the 1,4-dicarbonyl moiety in the resultant Michael adducts under different PaalKnorr conditions results in two new kinds of 3,3'-disubstituted oxindoles3-furanyl- and 3-pyrrolyl-3-alkyl-oxindolesin high yields and good enantioselectivities. Notably, the studies presented here sufficiently confirm that this two-step strategy of sequential conjugate addition/PaalKnorr cyclization is not only an attractive method for the indirect enantioselective heteroarylation of 3-alkyloxindoles, but also opens up new avenues toward asymmetric synthesis of structurally diverse 3,3'-disubstituted oxindole derivatives.
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