Asymmetric hetero Diels-Alder reaction using chiral cationic metallosalen complexes as catalysts

Chiral cationic (R,S)- or (R,R)-(salen)-manganese(III) and -chromium(III) complexes served as the catalysts for asymmetric hetero Diels-Alder reaction of Danishefsky's diene with aldehydes, achieving high enantioselectivity (up to 97% ee at 0 degreesC). The reactions of aldehydes bearing no precoordinating functional group were well effected by using (R,R)-complexes as catalysts, while those of aldehydes bearing a precoordinating functionality were better effected by using (R,S)-complexes. (C) 2001 Elsevier Science Ltd. All rights reserved.