作者:Maryellen Nerz-Stonies、Edward R. Thornton
DOI:10.1016/s0040-4039(00)84131-3
日期:1986.1
Directed aldol reactions of chiral (Me2CHO)3Ti-enolates give the opposite diastereofacial selectivity compared with the corresponding boron enolates. This stereochemical reversal is best explained if the Ti reactions involve chelation (not possible with boron, and previously thought to be unfavorable with (Me2CHO)3Ti-enolates). Changing the solvent from THF to diethyl ether significantly enhances the
与相应的硼烯醇酸酯相比,手性(Me 2 CHO)3钛烯醇酸酯的直接醛醇缩合反应具有相反的非对面选择性。如果Ti反应涉及螯合(对于硼是不可能的,以前被认为对(Me 2 CHO)3 Ti-烯酸酯不利),则最好解释这种立体化学逆转。将溶剂从THF更改为二乙醚显着增强了假设的螯合效果。因此,使用Ti或硼可以方便地合成任何一种产物对映异构体,从该手性助剂开始,该手性助剂的构型易于并廉价地衍生自天然来源。