Trimethyl borate → (1S,4S)-1,4-bis(4-chloro-3-nitrophenyl)butane-1,4-diol

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(R)-(+)-α,α-Diphenyl-2-pyrrolidinemethanol (1.08 g, 4.28 mmol) was dissolved in 70 mL of THF at ambient temperature in a dry flask under nitrogen and trimethyl borate (650 uL, 5.54 mmol) was added dropwise. The resulting solution was stirred for 1 hour. The solution was cooled in a cold bath to ˜10° C. and the N,N-diethylaniline borane (9.18 mL, 51.6 mmol) was added dropwise with some bubbling. After 15 minutes, this solution was transferred to an addition funnel and added dropwise to 1,4-bis(4-chloro-3-nitrophenyl)butane-1,4-dione (Intermediate 5B) (10.0 g, 25.2 mmol) suspended in 200 mL of THF and cooled to ˜10° C. Bubbling was observed. After the addition, the mixture was stirred at ambient temperature for 4 hours. The mixture was cooled in an ice bath and 30 mL or methanol was added dropwise until bubbling stopped, then the mixture was allowed to stir at ambient temperature for 30 minutes. The mixture was filtered to get rid of a trace of insoluble unreacted starting material. The filtrate was concentrated, poured into 1 M HCl and extracted into ethyl acetate, dried over sodium sulfate, and concentrated to give the title compound (9.9 g, 99%) as a yellow waxy solid. Chiral HPLC e.e. >99.9% (RR diol was undetectable). 1H NMR (400 MHz, DMSO-d6) δ ppm 7.94 (d, J=1.9 Hz, 2H), 7.69 (d, J=8.4 Hz, 2H), 7.60 (dd, J=8.4, 1.9 Hz, 2H), 4.65 (m, 2H), 1.62 (m, 4H).

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