Asymmetric synthesis of the stereoisomers of 2-amino-5-carboxymethyl-cyclopentane-1-carboxylate
作者:Julio G. Urones、Narciso M. Garrido、David Díez、Mohamed M. El Hammoumi、Sara H. Dominguez、J. Antonio Casaseca、Stephen G. Davies、Andrew D. Smith
DOI:10.1039/b313386a
日期:——
The stereoisomers of 2-amino-5-carboxymethyl-cyclopentane-1-carboxylate may be prepared stereoselectively from diester derivatives of (E,E)-octa-2,6-diendioc acid, with the key step utilising the conjugate addition of homochiral lithium N-benzyl-N-α-methylbenzylamide. The trans-C(1)–C(2)-stereoisomers are readily prepared via a diastereoselective tandem conjugate addition cyclisation protocol with lithium (R)-N-benzyl-N-α-methylbenzylamide, with subsequent hydrogenolysis and ester hydrolysis giving the (1R,2R,5R)- and (1R,2R,5S)-β-amino diacids in good yields. The preparation of the cis-C(1)–C(2)-stereoisomers utilises a protocol involving N-oxidation and Cope elimination of the major diastereoisomeric product arising from conjugate addition and cyclisation, giving homochiral (R)-5-carboxymethyl-cyclopentene-1-carboxylate. Conjugate addition of either lithium (R)- or (S)-N-benzyl-N-α-methylbenzylamide to (R)-5-carboxymethyl-cyclopentene-1-carboxylate, and diastereoselective protonation with 2,6-di-tert-butyl phenol gives, after hydrogenolysis and ester hydrolysis, the (1S,2R,5R)- and (1R,2S,5R)-β-amino diacids in good yield. The use of (S)-N-benzyl-N-α-methylbenzylamide in the initial conjugate addition and cyclisation reaction, and subsequent repetition of the elimination and conjugate addition strategy allows stereoselective access to all stereoisomers of 2-amino-5-carboxymethyl-cyclopentane-1-carboxylate.
2-氨基-5-羧甲基环戊烷-1-羧酸酯的立体异构体可以通过对(E,E)-辛烯-2,6-二羧酸的二酯衍生物进行立体选择性合成,关键步骤是利用手性锂N-苄基-N-α-甲基苄胺的共轭加成。trans-C(1)–C(2)-立体异构体通过与锂(R)-N-苄基-N-α-甲基苄胺的非对映选择性串联共轭加成环化反应容易制备,随后进行氢解和酯水解,从而良好收率地得到(1R,2R,5R)-和(1R,2R,5S)-β-氨基二酸。cis-C(1)–C(2)-立体异构体的制备涉及N-氧化和主要的由共轭加成和环化反应生成的非对映异构体的科普消除反应,得到手性(R)-5-羧甲基环戊烯-1-羧酸酯。无论是锂(R)-还是(S)-N-苄基-N-α-甲基苄胺与(R)-5-羧甲基环戊烯-1-羧酸酯进行的共轭加成,经过2,6-二-tert-丁基苯酚的非对映选择性质子化后,经过氢解和酯水解,能够以良好收率得到(1S,2R,5R)-和(1R,2S,5R)-β-氨基二酸。在初始的共轭加成和环化反应中使用(S)-N-苄基-N-α-甲基苄胺,并随后重复消除和共轭加成策略,可以立体选择性地获得所有2-氨基-5-羧甲基环戊烷-1-羧酸酯的立体异构体。