DIANANE‐CrIII‐salen Complexes as Highly Enantioselective Catalysts for Hetero‐Diels–Alder Reactions of Aldehydes with Dienes

A new type of chromium‐salen complex bearing DIANANE ( endo , endo ‐2,5‐diaminonorbornane) as chiral backbone has been synthesized and applied to the hetero‐Diels–Alder reaction of Danishefsky’s diene with various aldehydes. The reactions afford the corresponding 2‐substituted 2,3‐dihydro‐4 H ‐pyran‐4‐ones in high yields and enantioselectivities (up to 96 % ee ). The effect of different counteranions of the complex on reactivity as well as enantioselectivity has been investigated. Besides Danishefsky’s diene, reaction of the less reactive 1‐methoxybutadiene with benzaldehyde and ethyl glyoxylate can be effected by the chromium catalysts as well.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)