Organopalladium complex promoted asymmetric cycloaddition reactions involving 3,4-dimethyl-1-phenylphosphole 1-sulfide as the heterocyclic diene

Abstract

3,4-Dimethy]-l-phenylphosphole 1-sulfide (DMPPS) reacted as a heterocyclic diene in the asymmetric Diels-Alder reaction with diphenylvinylphosphine in the presence of an organopalladium(II) complex derived from the enantiomerically pure ortho-metalated (R)-(l-(dimethylamino)ethy)naphthalene. The cycloaddition reaction proceeded at room temperature via an intramolecular mechanism in which the cyclic diene and the dienophile were coordinated simultaneously on the chiral palladium template. The (Rp)-exo cycloadduct was obtained with high stereoselectivity as a P-S bidentate chelate on the palladium template. When DMPPS was treated with the heterodienophile thiobenzophenone at 50 °C in the presence of the organopalladium(II) complex, the corresponding heterocycloaddition reaction proceeded to generate the expected cycloadduct as a rigid S-S bidentate chelate on the palladium template. However, the cyclic adduct was obtained as a racemic mixture. The low stereoselectivity in the heterocycloaddition reaction is attributed to the kinetic instability of S→Pd coordination bonds in the intermediate template complex. Both the P-S and S-S cycloadducts could be liberated from the corresponding template complexes by treatment of the template complexes with aqueous potassium cyanide.