Background and overview[1]
Racemic or chiral diphosphine 5,5′-bis(diphenylphosphonium)-tetrafluoro-di-1,3-phenylenedioxetane is used as a bidentate ligand in the synthesis of metal complexes The isomer, used as a catalyst for asymmetric catalytic hydrogenation, has the advantage that the asymmetric induction directly leads to the preparation of optically pure isomers without the need for resolution of the racemic mixture.
Preparation[1]
5,5′-Bis(diphenylphosphorus)-tetrafluoro-bis-1,3-benzenedioxeterocycle can be prepared according to the following steps:
1) Place 5g benzodioxane and 100ml anhydrous tetrahydrofuran under argon in the dark. Then add 5.12g dibromodimethylhydantoin, stir the reaction mixture at room temperature in the dark for 18 hours, evaporate half of the tetrahydrofuran of the smooth opening agent, add 50ml pentane, filter, repeat the operation three times, and then The solvent was evaporated under reduced pressure. The obtained oily residue was purified by silica gel column chromatography, eluting with a mixture of cyclohexane/ethyl acetate 8/2, v/v (yield = 90%), to prepare 4-bromo-1,2-ethylenedioxy benzene.
2) Place 4-bromo-1,2-ethylenedioxybenzene, chlorodiphenylphosphine and 200 ml of anhydrous dimethylformamide under argon at 0°C. Then 54.9 g of bromosuccinimide was added in portions. After gradually returning to room temperature, the reaction mixture was stirred for 24 hours. The solvent was evaporated under reduced pressure and the white solid obtained was washed with dichloromethane. The filtrate was treated with 50 ml of saturated aqueous sodium sulfate solution, washed with 50 ml of saturated aqueous sodium chloride solution, and dried over magnesium sulfate. After evaporation of the solvent under reduced pressure, 5,5′-bis(diphenylphosphorus)-tetrafluoro-bis-1,3-benzenedioxeterocycle was obtained as a yellow oil (quantitative yield).
