Ethylene → Methyl (2S)-2-(tert-butoxycarbonylamino)-3-[4-(1,3,4-trimethyl-2,6-dioxo-pyrimidin 5-yl)phenyl]propanoate

Participants

Reaction Steps

To a suspension of zinc dust (800 mmol, 52.29 g) in THF (26.0 mL) was added 1,2-dibromoethane (53.2 mmol, 4.58 mL) at room temperature. This suspension was heated to 60-65° C. with a heat gun until evolution of ethylene gas ceased (observed). The suspension was cooled to room temperature, trimethylchlorosilane (26.6 mmol, 3.38 mL) was added and the mixture was stirred for 15 min. A suspension of 5-iodo-1,3,6-trimethyl uracil (266 mmol, 74.6 g) in DMA (225 mL) was warmed to obtain a clear solution and was added in one portion to the reaction mixture. After addition, the mixture was heated to 70° C. The internal temperature of the reaction mixture rose to 80-85° C. due to the exothermic reaction. The reaction mixture was stirred at 70° C. for 3-4 h at which time TLC of an aliquot which had been quenched with saturated ammonium chloride indicated the absence of starting material. The reaction mixture was diluted with THF (140 mL), was cooled to room temperature and the excess zinc dust was allowed to settle over 2-3 h. This solution containing the zinc compound (266 mmol) was added to a solution of Pd(dba)2 (8 mmol, 4.6 g), tri-o-tolylphosphine [P(Tol)3] (29.6 mmol, 9.0 g) and N-[(1,1-dimethylethoxy)carbonyl]-4-iodo-L-phenylalanine methyl ester (186 mmol, 75.56 g) in THF (280 mL) at room temperature and the light yellow mixture was stirred for 48 h at 50-55° C. The reaction mixture was poured into a saturated ammonium chloride solution and was extracted with ethyl acetate (3×750 mL). The combined extracts were washed with brine solution (1.5 L) and dried over anhydrous magnesium sulfate. Filtration of the drying agent and concentration gave the crude product which was purified by silica gel column chromatography using a Biotage (75m) column to obtain 57.88 g (72% yield) of N-[(1,1-dimethylethoxy)carbonyl]-4-(1,3,6-trimethyl-2,4-dioxo-5-pyrimidinyl)-L-phenylalanine methyl ester as an amorphous white solid. EI-HRMS m/e calcd for C22H29N3O6 (M+) 431.2056, found 431.2054.

Provenance & Evidence