A comparison of palladium complexes of BINAP and diphenylphosphinooxazoline ligands in the catalytic asymmetric synthesis of cis-decalins

BINAP and a range of oxazoline-containing phosphinamine ligands were screened in the palladium-catalysed asymmetric intramolecular Heck cyclisation to form cis-decalins. Complexes formed from Pd2(dba)3 and BINAP gave cyclised products in up to 65% yield and 85% ee. The t-leucine-derived diphenylphosphinoferrocenyloxazoline ligand afforded our optimal enantioselectivity of 85% for the range of phosphinamine ligands tested. Variation of solvent and base appears to indicate that this system is sensitive to catalyst deactivation and that a combination of either toluene or N-methylpyrrolidine with potassium carbonate as base was required for acceptable catalytic activity. Catalysts prepared from palladium complexes of diphenylphosphinoaryloxazoline ligands were less reactive than the corresponding BINAP catalysts as the optimal yield obtained was 47%.