C₂-symmetric bisamidines: Chiral Brønsted bases catalysing the Diels- Alder reaction of anthrones

• Deniz Akalay,
• Gerd Dürner,
• Jan W. Bats and
• Michael W. Göbel

Beilstein J. Org. Chem. 2008, 4, No. 28, doi:10.3762/bjoc.4.28

• compounds 2 could be introduced by a Mitsunobu alkylation of maleimide [12]. Alternatively, substituted maleimides were prepared by reaction of maleic anhydride with the corresponding amines followed by ring closure [13][14]. Cycloaddition kinetics of 1a and 2a was examined first by 1H NMR in CD2Cl2 at room

• yields and with moderate values of ee. A remarkable increase in enantioselectivity was observed using maleimide 2i. The steric hindrance imposed by the large 2,6-diisopropylphenyl moiety of 2i resulted in 76% ee at −70 °C but also lowered reaction rates. Only 13% yield could be obtained under such