Tris(1,1-dimethylethyl)phosphine → 4-[4-(4-(Benzyloxycarbonyl)piperazin-1-yl)phenyl]-3,4-dihydro-2H-quinoxaline-1-carboxylic acid tert-butyl ester

Participants

Reaction Conditions

Reaction Steps

8.43 g of 4-(4-bromophenyl)piperazine-1-carboxylic acid benzyl ester are placed in a 500 ml three-necked flask under a nitrogen atmosphere. 170 ml of anhydrous o-xylene, 5.01 g of 3,4-dihydro-2H-quinoxaline-1-carboxylic acid tert-butyl ester and then 3.08 g of sodium tert-butoxide are added, followed by 0.48 g of palladium acetate, and then the addition is completed with 0.53 ml of tri(tert-butyl)phosphine. The reaction mixture is heated at 150° C. for 18 h. Heating is halted and the mixture is brought back to ambient temperature. The o-xylene is evaporated and the mixture is taken up in ethyl acetate before filtering it through celite. The organic phase is washed with water and then with a saturated aqueous sodium chloride solution. The aqueous phase is extracted with ethyl acetate. The organic phases are combined and then dried over sodium sulphate, filtered through a sintered glass filter and concentrated under vacuum. 8.9 g of 4-[4-(4-(Benzyloxycarbonyl)piperazin-1-yl)phenyl]-3,4-dihydro-2H-quinoxaline-1-carboxylic acid tert-butyl ester are obtained after purification on a silica column, elution being carried out with a gradient of heptane/ethyl acetate solvent varying from 95/5 to 60/40).

Provenance & Evidence