Double diastereoselection in asymmetric [2+3] cycloaddition of chiral oxazoline N-oxides: application to the kinetic resolution of a racemic α,β-unsaturated δ-lactone
作者:Olivier Dirat、Cyrille Kouklovsky、Yves Langlois、Philippe Lesot、Jacques Courtieu
DOI:10.1016/s0957-4166(99)00317-1
日期:1999.8
The asymmetric [2+3] cycloaddition reaction between chiral oxazoline N-oxide 1 and α,β-unsaturated lactone 2 was studied. A double diastereoselection was observed, (1R)-1 and (R)-2 gave a mismatched pair with almost no cycloadduct obtained. A transition state model is proposed, accounting for the destabilization of transition state in the cycloaddition reaction. This result has led to kinetic resolution
研究了手性恶唑啉N-氧化物1与α,β-不饱和内酯2的不对称[2 + 3]环加成反应。观察到两次非对映选择性,(1 R)-1和(R)-2产生不匹配的对,几乎没有获得环加合物。提出了过渡态模型,该模型考虑了环加成反应中过渡态的不稳定。该结果导致了动力学拆分研究,其中两个对映异构体1与外消旋内酯2反应。回收的内酯2的对映体过量被确定为不超过70%ee在手性液晶溶剂中的13 C- 1 H} NMR分析。实验结果与预测的对映异构体过量一致并且与过渡态模型一致。