Asymmetric synthesis of 3-substituted 3,4-dihydroisocoumarins via stereoselective addition of laterally lithiated chiral 2-(o-tolyl)oxazolines to aldehydes followed by diastereomer-selective lactonization
作者:Yuji Kurosaki、Tsutomu Fukuda、Masatomo Iwao
DOI:10.1016/j.tet.2005.01.103
日期:2005.3
Lateral lithiation of (S)-4-isopropyl-2-(o-tolyl)oxazoline in diethyl ether followed by the reaction with aldehydes in the presence of TMEDA produced the addition products with stereoselectivities up to 84% de. Utilization of TMEDA as a ligand is essential for the good selectivity. Rationale for the stereoselectivity is proposed based on ab initio calculation of the lateral lithio species. The major
(S)-4-异丙基-2-(邻甲苯基)恶唑啉在乙醚中的侧向锂化,然后在TMEDA存在下与醛反应,产生了立体选择性高达84%de的加成产物。使用TMEDA作为配体对于良好的选择性至关重要。基于侧向硫基物质的从头算,提出了立体选择性的理由。在酸性条件下,主要的(S,S)产物内酯化的速度比次要的(S,R)产物内酯化更快。因此,(3 S通过顺序应用这些匹配的立体选择性反应,可以得到高达97%ee的高光学纯度的)-3,4-二氢异香豆素。