Metal template effects on the asymmetric cycloaddition reaction between diphenylvinylphosphine and 2-diphenylphosphinofuran

Abstract

The organoplatinum complex containing ortho-metalated (S)-(1-(dimethylamino)ethyl)-naphthalene as the chiral auxiliary has been used efficiently to promote the asymmetric [4 + 2] Diels-Alder reaction between diphenylvinylphosphine and 2-diphenylphosphinofuran to generate the chelating diphosphine exo-cycloadduct, 4(R)-bis(diphenylphosphino)-7-oxabicyclo[2.2.1]hept-2-ene in 70% isolated yield. At room temperature, the reaction was complete in 5 d. However, the cycloaddition reaction proceeded at a significantly slower rate and exhibited a markedly lower stereoselectivity when the chiral platinum template was replaced by its organopallodium counterpart. The diphosphino-substituted oxanorbornene metal complexes are stable and the oxygen-carbon bonds are inert toward treatments with strong acids. Upon liberation from the metal ions, however, the chiral cycloadduct becomes unstable and undergoes the retro Diels-Alder reaction slowly to regenerate diphenylvinylphosphine and 2-diphenylphosphinofuran.