A reliable phosphonium-based PTC: For the first time a chiral quaternary tetraalkylphosphonium salt has successfully been used as a phase-transfer catalyst (PTC) for asymmetric amination of β-keto esters, in high yield and with high ee (see scheme). Asymmetric amination of a cyclic five-membered β-keto ester is a valuable method for preparing a key intermediate for asymmetric synthesis of aldose reductase inhibitor AS-3201 (Ranirestat).
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