PALLADIUM-CATALYZED ASYMMETRIC ARYLATION OF 2,3-DIHYDROFURAN WITH PHENYL TRIFLATE - A NOVEL ASYMMETRIC CATALYSIS INVOLVING A KINETIC RESOLUTION PROCESS

The reaction of phenyl triflate and 2,3-dihydrofuran in benzene in the presence of a base and a palladium catalyst coordinated with (R)-BINAP gave optically active (R)-2-phenyl-2,3-dihydrofuran (1a) and a small amount of (S)-2-phenyl-2,5-dihydrofuran (2a). The two regioisomers have configurations opposite to each other. A clear correlation was observed between the enantioselectivity and the regioselectivity. Thus, the enantiomeric purity of (R)-1a increases as the ratio of (S)-2a to (R)-1a increases. A catalytic mechanism involving a kinetic resolution process is proposed to account for the relation. Factors controlling the regio- and enantioselectivities are discussed in detail using molecular models based on the X-ray structure of PdCl2-{(R)-BINAP}. Crystal data for PdCl2{(R)-BINAP}: C44H32Cl2P2Pd, a = 11.751(1) angstrom, c = 26.538(3) angstrom, V = 3664.2 angstrom3, tetragonal, P4(1), Z = 4.