Hetero‐Diels−Alder Reactions of Ketones — A Challenge for Chemists

The recent developments of mainly catalytic and enantioselective hetero‐Diels−Alder reactions of ketones are presented. First, direct reactions of unactivated ketones are presented, focusing on the recent hydrogen bond‐promoted hetero‐Diels−Alder reactions with activated conjugated dienes. Then, direct catalytic enantioselective hetero‐Diels−Alder reactions of activated ketones with conjugated dienes are outlined. The use of different chiral copper( II ) and zinc( II ) catalysts are shown and the use of the hetero‐Diels−Alder adducts in organic synthesis presented. Finally, the inverse‐electron demand hetero‐Diels−Alder reactions of α,β‐unsaturated ketone functionalities are discussed. The different chiral Lewis‐acid complexes and chiral amines used for catalytic asymmetric hetero‐Diels−Alder reactions are presented and the scope of these reactions in the synthesis of optically active α‐hydroxy lactones, formyl esters and carbohydrates are demonstrated. The mechanistic aspects of the catalytic enantioselective hetero‐Diels−Alder reactions are also discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)