Thionyl Chloride → (S)-benzyl-{1-[[2-(o-fluorobenzoyl)-4-nitrophenyl]carbamoyl]ethyl}carbamate

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Reaction Steps

120 g of carbobenzoxy-L-alanine are dissolved in 800 ml of absolute tetrahydrofuran, treated dropwise while cooling with ice with 70 g of thionyl chloride and stirred for 40 minutes while cooling with ice. There is then rapidly added dropwise thereto a suspension of 100 g (0.38 M) of 2-amino-5-nitro-2'-fluorobenzophenone in 400 ml of absolute tetrahydrofuran and the mixture is stirred at room temperature for 24 hours. The solution obtained is concentrated and the residue is treated with ice and 10% sodium bicarbonate solution and extracted with methylene chloride. The organic solution is dried over sodium sulphate, filtered and concentrated. The residue is dissolved in a small amount of methylene chloride and treated with ether. There is obtained (S)-benzyl-{1-[[2-(o-fluorobenzoyl)-4-nitrophenyl]carbamoyl]ethyl}carbamate. A further recrystallisation from methylene chloride/ether yields a product which melts at 158°-160° C. and shows a rotation of [α]25D =-23.4° (in methylene chloride; 1%). The mother liquors are purified on a 600 g in silica gel column using methylene chloride as the eluting agent, an additional amount of the aforementioned product being obtained.

Provenance & Evidence