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

The organoplatinum complex containing ortho-metalated (S)-(l-(dimethylamino )ethyl)naphthalene as the chiral auxiliary has been used efficiently to pro mote the asymmetric [4 + 2] Diels-Alder reaction between diphenylvinylphosp hine and 2-diphenylphosphinofuran to generate the chelating diphosphine exo -cycloadduct, 4(R),5(R)-bis(diphenylphosphino)-7-oxabicyclo [2.2.1]hept-2-e ne in 70% isolated yield. At room temperature, the reaction was. complete i n 5 d. However, the cycloaddition reaction proceeded at a significantly slo wer:rate and exhibited a markedly lower stereoselectivity when the chiral p latinum template was replaced by its organopalladium counterpart. The dipho sphino-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 diphenylvinyl phosphine and 2-diphenylphosphinofuran.