Diastereofacial selectivity in Diels-Alder reactions of a diene having a stereogenic centre carrying a silyl group adjacent to the diene system

The dienylmethylsilane (3) reacts with N-phenylmaleimide to give the adducts (4) and (5) in a ratio of 82:18, the major product having come from reaction with diastereoface selectivity in the sense (18). The same diene, however, reacts with dimethyl acetylenedicarboxylate in the opposite sense (19) to give only the adduct (25). These results are not only complementary to each other but are also complementary to the reactions of the dienes (6) and (22), having an oxygen substituent on the stereogenic centre in place of the silyl group, where the major reaction of (6) with N-phenylmaleimide is known to take place in the sense (20), and the major reaction of (22) with dimethyl acetylenedicarboxylate in the opposite sense (21).