Triphenylphosphine → (S)-3-[5-(1-t-butoxycarbonylamino-2-biphenyl-4-yl-ethyl)tetrazol-1-yl]-propionitrile

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Reaction Steps

To a stirred solution of (S)-2-t-butoxycarbonylamino-3-biphenyl-4-yl-N-(2-cyanoethyl)-propionamide (18 g, 45.7 mmol) in THF (375 mL) under nitrogen is added triphenylphosphine (12 g, 45.7 mmol). The solution is cooled to 0° and treated with diethyl azodicarboxylate (DEAD, 7.2 mL, 24.3 mmol) followed by trimethylsilyl azide (3.2 mL, 24.3 mmol). The solution is warmed up to room temperature and stirred for 18 hours. One additional equivalent of triphenyl phosphine (12 g, 45.7 mmol), DEAD (7.2 mL, 24.3 mmol) and trimethylsilyl azide (3.2 mL, 24.3 mmol) are added and stirring is continued for 3 days. The solution is cooled to 0°. Ceric ammonium nitrate (2.2 L; 10% aqueous solution) is added dropwise. After 20 minutes of stirring, extraction is carried out with methylene chloride (3×200 mL). The combined organic layers are dried over anhydrous sodium sulfate, then filtered and concentrated in vacuo. The residue is taken up in ethyl acetate (500 mL) and hexane (50 mL). A small amount of (S)-3-[5-(1-t-butoxycarbonylamino-2-biphenyl-4-yl-ethyl)-tetrazol-1-yl]-propionitrile crystallizes out. The filtrate is concentrated and the residue purified by flash-chromatography eluting with a gradient of ethyl acetate in hexane (30% to 50%). The pure fractions of product (Rf=0.6 in 1/1 ethyl acetate/hexane) are combined and concentrated under reduced pressure to give (S)-3-[5-(1-t-butoxycarbonylamino-2-biphenyl-4-yl-ethyl)-tetrazol-1-yl]-propionitrile as a colorless crystalline solid, m.p. 184°-185°, [α]D =-2.90° (c 0.89, CHCl3).

Provenance & Evidence