Parallel kinetic resolution of tert-butyl (RS)-3-alkyl–cyclopentene-1-carboxylates for the asymmetric synthesis of 3-alkyl–cispentacin derivatives
作者:Stephen G. Davies、A. Christopher Garner、Marcus J. C. Long、Andrew D. Smith、Miles J. Sweet、Jonathan M. Withey
DOI:10.1039/b407560a
日期:——
The double mutual kinetic resolution of tert-butyl (RS)-3-benzylâcyclopentene-1-carboxylate with a 50 : 50 mixture of lithium (RS)-N-benzyl-N-α-methylbenzylamide and lithium (RS)-N-3,4-dimethoxybenzyl-N-α-methylbenzylamide gives, after protonation with 2,6-di-tert-butylphenol, a 50 : 50 mixture of the readily separable N-benzyl-(1SR,2RS,3RS,αRS)- and N-3,4-dimethoxybenzyl-(1SR,2RS,3RS,αRS)-β-amino esters in >98% de in each case. This product distribution indicates that these amides react at very similar rates and with no mutual interference to furnish readily separable products, and are thus ideal for parallel kinetic resolution. The efficient parallel kinetic resolution (E > 65) of a range of tert-butyl (RS)-3-alkylâcyclopentene-1-carboxylates with a pseudoenantiomeric mixture of homochiral lithium (S)-N-benzyl-N-α-methylbenzylamide and lithium (R)-N-3,4-dimethoxybenzyl-N-α-methylbenzylamide gives, after separation and N-deprotection, a range of carboxylate protected 3-alkylâcispentacin derivatives in >98% de and >95% ee.
(RS)-3-苄基环戊烯-1-甲酸叔丁酯与(RS)-N-苄基-N-δ-甲基苄基酰胺锂和(RS)-N-3,4-二甲氧基苄基-N-δ-甲基苄基酰胺锂的 50 : 50 混合物进行双互动力学解析,在与 2,6-二叔丁基苯酚质子化后,得到 50 :50 的混合物,其中 N-苄基-(1SR,2RS,3RS,δRS)-和 N-3,4-二甲氧基苄基-(1SR,2RS,3RS,δRS)-δ-氨基酯的分离度均大于 98%。这种产物分布表明,这些酰胺的反应速度非常接近,而且没有相互干扰,生成的产物很容易分离,因此非常适合平行动力学解析。用同手性的(S)-N-苄基-N-δ-甲基苄基酰胺锂和(R)-N-3-苄基-N-δ-甲基苄基酰胺锂的假对映体混合物对一系列(RS)-3-烷基环戊烯-1-甲酸叔丁酯进行高效的平行动力学解析(E > 65)、4-二甲氧基苄基-N-δ-甲基苄酰胺的假对映体混合物,经分离和 N-脱保护后,得到一系列羧酸盐保护的 3-烷基肉毒碱衍生物,de>98%,ee>95%。