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DOI: 10.1055/s-2007-992432
Diels-Alder Reaction of Nitroolefins
Contributor(s):Benjamin List, Corinna ReisingerStockholm University, Sweden
Direct Enantioselective Synthesis of Bicyclic Diels-Alder Products
Adv. Synth. Catal. 2007, 349: 2549-2555
Publication History
Publication Date:
23 January 2008 (online)
Key words
Diels-Alder reaction - nitroolefins - aminocatalysis - Michael addition
Significance
The diastereoselective and enantioselective formation of bicyclic Diels-Alder products 4 starting from α,β-unsaturated cyclic ketones 1 of different ring sizes and (hetero)aromatic nitroolefins 2 is described. Aliphatic nitroolefins give only traces of product. Commercially available, chiral diamine 3 in combination with DNBSA was used as catalyst. In accordance with the observed absolute stereochemistry, the reaction is suggested to proceed via a stepwise domino double Michael addition pathway. Alternatively, a concerted Diels-Alder mechanism may be considered.
Comment
Domino reactions are a powerful tool for assembling complex molecules in a single operation. The dual, yet interdependent activation ability of amines (enamine and iminium-ion formation) makes amine catalysts ideal for application in domino reactions (see review below). Current limitations of the method presented by the Córdova group are the moderate enantioselectivities (ee values mostly in the seventies) and the restriction to (hetero)aromatic nitroolefins. A conceptually similar aza-Diels-Alder reaction has earlier been developed by the same group (Angew. Chem. Int. Ed. 2005, 44, 4877).
Review
B. List Chem. Commun. 2006, 819.