Cationic Palladium/Boxax Complexes for Catalytic Asymmetric Wacker-Type Cyclization

Catalyticasymmetric Wacker-type cyclization of 2-(2,3-dimethyl-2-butenyl)phenol ( 1a ) was efficiently catalyzed by 1 or 2 mol % of a cationic palladium−boxax complex generated in situ by mixing Pd(CH 3 CN) 4 (BF 4 ) 2 with ( S, S )-ip-boxax ( 3a ) in the presence of p -benzoquinone to give ( S )-(−)-2-isopropenyl-2-methyl-2,3-dihydrobenzofuran ( 2a ) in 94−96% ee and 45−85% yield. An X-ray diffraction study of the crystal structure of Pd(OCOCF 3 ) 2 {( S, S )-ip-boxax} ( 6 ) revealed that the orientation of alkyl substituents on the boxax ligand is perpendicular to the plane of the square planar complex.