PALLADIUM-COMPLEX-PROMOTED ASYMMETRIC-SYNTHESIS OF STEREOISOMERIC P-CHIRAL PYRIDYLPHOSPHINES VIA AN UNUSUAL EXO-ENDO STEREOCHEMICALLY CONTROLLED ASYMMETRIC DIELS-ALDER REACTION BETWEEN 2-VINYLPYRIDINE AND COORDINATED 3,4-DIMETHYL-1-PHENYLPHOSPHOLE

The organopalladium complex containing ortho-metalated (S)-( 1-(dimeth ylamino)ethyl)naphthalene as the chiral auxiliary has been used succes sfully to promote the asymmetric [4 + 2] Diels-Alder reaction between 3,4-dimethyl-1-phenylphosphole and 2-vinylpyridine. The pyridyl group in the resulting phosphanorbornene cycloadducts can be located stereos pecifically in the exo or endo position by controlling the electronic properties of the organopalladium promoter. In the exo-cycloaddition p rocess, the P-N bidentate ligand (-)-2-[(1 alpha,2 alpha(S),4 yl-7-pho sphabicyclp[2.2.1]hept-5-ene-2-yl]pyridine was produced stereoselectiv ely. In the endo-cycloaddition process, however, a pair of separable d iastereomeric palladium template complexes containing the naphthylamin e auxiliary and the enantiomeric forms of 2-[(1 alpha,2 beta(R/S),4 l- 7-phosphabicyclo-[2.2.1]hept-5-ene-2-yl]pyridine were obtained. In the se diastereomeric complexes, the endo-cycloadducts coordinated on pall adiun as monodentate ligands via only their phosphorus donor atoms. Th e pyridyl-nitrogen atoms are not involved in metal complexation. The a bsolute configurations and the coordination properties of the exo- and endo-pyridylphosphines have been established by single-crystal X-ray analyses.