Benzenemethanethiol, alpha,alpha-diphenyl- → (2S,4R)-4-Tritylsulfanyl-pyrrolidine-1,2-dicarboxylic acid 1-tert-butyl ester 2-methyl ester

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A solution of 76 g (0.68 mol) potassium-tert.-butylate in 1.5 l DMF was cooled (−3° C.) and treated slowly (1.5 h) with 202 g (0.73 mol) triphenylmethanethiol in 0.8 l DMF (at max 1° C.). After 2.5 h at 0° C., a solution of 161 g (0.61 mol) of (2S,4S)-4-Chloro-pyrrolidine-1,2-dicarboxylic acid 1-tert-butyl ester 2-methyl ester in 0.35 l DMF was added. The reaction was stirred over night at 2° C., evaporated, dissolved in 1.5 l EtOAc, poured into 2.7 l aqueous saturated NH4Cl solution and extracted with EtOAc (2×). The organic phase was washed with aqueous saturated NaHCO3, dried over Na2SO4 and evaporated. Chromatography on silicagel with hexane/EtOAc (95:5 to 7:3) gave 268 g (87%) (2S,4R)-4-Tritylsulfanyl-pyrrolidine-1,2-dicarboxylic acid 1-tert-butyl ester 2-methyl ester, MS: 504 (MH+).

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