N-Phenylmaleimide undergoes Diels-Alder cycloaddition predominantly to the face of cis- cyclohexa-3, 5-diene-1, 2-diol (3) syn to the oxygen functions. Derivatization can be used to alter the π-facial diastereoselectivity in a synthetically useful manner. The best cases are the exclusive, high yield, production of the syn-addition product with the trimethylsilyl ether derivative (8), and the exo-benzylidine derivative (26) gave a 96: 4 anti/syn ratio of ...
