MOLECULAR-SIEVE CONTROLLED DIASTEREOSELECTIVITY - EFFECT IN THE PALLADIUM-CATALYZED CYCLIZATION OF CIS-1,2-DIVINYLCYCLOHEXANE WITH ALPHA-OXYGEN-SUBSTITUTED ACIDS AS CHIRAL NUCLEOPHILES

Molecular sieves have been shown to improve greatly the stereoselectivity in the palladium(II)-catalyzed reaction of cis-1,2-divinylcyclohexane with chiral acids. Reactions run with molecular sieves and derivatives of (R)-lactic acids as nucleophiles always yielded products with S configuration at the newly formed chiral center in contrast to reactions without molecular sieves that gave products with either S or R configuration at this chiral center. It appears that this effect has not been observed previously. Only water-containing molecular sieves increased the stereoselectivity. A chiral palladium complex was formed faster in the presence of molecular sieves, but use of this complex as catalyst in the cyclization did not result in increased selectivity. The best stereoselectivity was found for molecular sieves with a high sodium content (Lancaster 13X and 4-angstrom sieves).