Asymmetric Diels‐Alder Cycloadditions with Chiral Carbamoyl Dienophiles

Chiral acylnitroso dienophiles 14, which were obtained from L‐proline and from D‐mandelic acid, reacted with cyclohexa‐1,3‐diene to give the expected diastereoisomers 15 and 16 (Scheme 2 and Table 1). The d.e. values for these Diels‐Alder reactions were moderate; they are related to the molecular stiffness of the dienophiles. The absolute configuration of the major cycloadducts was interpreted in terms of HOMO/LUMO interactions, the approach being ‘endo’ and the acylintroso dienophiles reacting from their s‐cis‐conformation.