Lawesson's reagent → methyl (2S)-4-[bis(2-{[(tert-butoxy)carbonyl]amino}ethyl)carbamothioyl]-2-{[(tert-butoxy) carbonyl]amino}butanoate

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Reaction Steps

To the solution of methyl (2S)-4-[bis(2-{[(tert-butoxy)carbonyl]amino}ethyl)carbamoyl]-2-{[(tert-butoxy)carbonyl]amino}butanoate XIV (610 mg, 1.12 mmol) in THF (10 mL) under argon was added Lawesson's reagent (680 mg, 1.68 mmol) and DMAP (13 mg, 0.11 mmol). The mixture was stirred at r.t. for 2 h and then refluxed over weekend. An additional two portions of Lawesson's reagent (900 mg, 2.24 mmol) and was added and the reaction was refluxed for another 4 h. The solvent was evaporated under reduced pressure and the crude product was purified on a silica gel column (1:6 EtOAc/hexane) to give methyl (2S)-4-[bis(2-{[(tert-butoxy)carbonyl]amino}ethyl)carbamothioyl]-2-{[(tert-butoxy)carbonyl]amino}butanoate XV (290 mg, 0.51 mmol, 45% yield). ESIMS found for C25H46N4O8S m/z 563 (M+H).

Provenance & Evidence