Enantioselective elimination reaction of a 6,6-membered bicyclic allylic carbonate. Importance of chirality reversal depending on the palladium-chiral phosphine ratio

Reaction of (±)-8α-methoxycarbonyloxy-4aβ-methyl-2,3,4,4a,5,6,7,8-octahydronaphthalene ( 1 ) in the presence of a palladium-chiral phosphine catalyst gave 4a-methyl-3,4,4a,5,6,7-hexahydronaphthalene ( 2 ) enantioselectively. When the reaction was carried out using Pd(OAc) 2 and ( S )-(−)-BINAP, the enantioselection was influenced by the phosphine to palladium ratio, because ( S )-BINAP oxide generated in situ acted as a ligand causing the opposite enantioselectivity. High enantioselectivity (86% ee) was obtained when (1-Me-C 3 H 5 -PdCl) 2 and ( S )-(−)- p -Tol-BINAP were used.