Practical enantioselective synthesis of beta-substituted-beta-amino esters |
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Authors: | Awasthi Alok K Boys Mark L Cain-Janicki Kimberly J Colson Pierre-Jean Doubleday Wendel W Duran Joseph E Farid Payman N |
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Institution: | Pfizer Global Research & Development, Pfizer Inc., Ann Arbor, Michigan 48105, USA. alok.k.awasthi@pfizer.com |
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Abstract: | reaction: see text] A practical, large-scale synthesis of a beta-amino ester 1 was developed. A chiral imine derived from (S)-phenylglycinol and 3-trimethylsilylpropanal was coupled with the Reformatsky reagent 3 with high diastereoselectivity (de > 98%) to give (SS)-4a as the major isomer. The amino alcohol residue of the coupling product 4 was oxidatively cleaved with sodium periodate in the presence of methylamine. An unusual selective oxidative cleavage of the (SS)-isomer was observed and the imine 6 was obtained with ee > 99% while the (RS)-4b isomer was not cleaved. Reaction with p-toluenesulfonic acid monohydrate allowed for the hydrolysis of the imine and the isolation of the amine as its salt. The title compound 1 was then obtained by transesterification, desilylation, and hydrochloride salt formation in a one-pot process. The method was successfully applied toward the synthesis of a wide variety of beta-amino esters. |
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