Asymmetric synthesis of chiral arsines and phosphines and their stability investigation

Abstract

The organopalladium complex containing ortho-metalated (S)-[1-(dimethylamino)ethyl]naphthalene (+)-41 as the chiral auxiliary has been successfully used as the chiral template to promote the asymmetric cycloaddition reactions between 3,4-dimethyl-1-phenylarsole (DMPA) and several kinds of vinylphosphines [diphenylvinylphosphine, (Z/E)-diphenyl-1-propenylphosphine, (Z/E)-diphenyl-1-styrylphosphine, phenyldivinylphosphine, diphenylvinylphosphine oxide, diphenylvinylphosphine sulphide], diphenylvinylarsine and ethyl vinyl ketone. For example, a diphenylphosphino-substituted asymmetrical heterobidentate arsanorbornene (As–P) ligand (–)-46 was obtained stereoselectively via asymmetric cycloaddition reaction between DMPA and diphenylvinylphosphine. In contrast to their reported P–P analogue, the arsenic donor in the dichloro complex [(As–P)PdCl2] (–)-45 could be eliminated stereospecifically under mild reaction conditions to generate the corresponding 1-(diphenylphosphino)-3,4-dimethyl-2,4-cyclohexadiene, which remained as a bidentate ligand at the PdCl2 unit via phosphorus and the η2-C4–C5 double bond [(+)-118]. The arsenic–elimination process was found to be influenced by the halo ligand in [(As–P)PdX2] [X = Cl, Br or I]. We then investigated further the template, metal ion and substituent effects on the similar asymmetric cycloaddition reactions.