Synthetic Approach To Substituted Cyclopropanes Based on the Coupling Reaction of Lithiated Chloroalkyloxazolines with Fischer Carbene Complexes
作者:Saverio Florio、Filippo M. Perna、Renzo Luisi、José Barluenga、Félix Rodríguez、Francisco J. Fañanás
DOI:10.1021/jo049613a
日期:2004.8.1
Regioselective addition of lithiated oxazoline 2a, easily available from 2-(1-chloroethyl)-4,4-dimethyl-2-oxazoline 1a (LDA, THF, −98 °C), to α,β-unsaturated Fischer carbene complexes 3 afforded cyclopropylcarbene complexes 4 as sole diastereoisomers. Exposure of carbene complexes 4a−c (M = Cr) to air and sunlight gave cyclopropane carboxylate derivatives 5a−c. A plausible mechanistic explanation is
区域选择性加成锂化恶唑啉2a中,容易获得,由2-(1-氯乙基)-4,4-二甲基-2-恶唑啉1A(LDA,THF,-98℃),α,β -不饱和的费卡宾络合物3,得到环丙基卡宾配合物4是唯一的非对映异构体。卡宾络合物4a - c(M = Cr)暴露于空气和阳光下,得到环丙烷羧酸酯衍生物5a - c。提出了一个合理的机械解释。此外,当在卡宾配合物3a存在下由1b生成锂化的恶唑啉2b时,b,恶唑啉基环丙烷羧酸酯6a,b以非对映异构体的1:1混合物形式形成。手性锂化的恶唑啉2c区域选择性地和非对映地添加至铬配合物3a,b和钨配合物3d,e,在金属片段氧化后,以良好的非对映选择性(dr = 4:1)形成酯7a,b。锂化的恶唑啉2d与铬配合物3b和钨配合物3e的反应非对映选择性较低,在两种情况下氧化后均提供酯7c 作为3:2非对映选择性混合物。