Diastereoselective alkylation of β-amino esters:: Structural and rate studies reveal alkylations of hexameric lithium enolates

被引:46
作者
McNeil, AJ
Toombes, GES
Gruner, SM
Lobkovsky, E
Collum, DB [1 ]
Chandramouli, SV
Vanasse, BJ
Ayers, TA
机构
[1] Cornell Univ, Dept Chem & Chem Biol, Baker Lab, Ithaca, NY 14853 USA
[2] Cornell Univ, Dept Phys, Ithaca, NY 14853 USA
[3] Aventis, Proc Dev Chem, Bridgewater, NJ 08807 USA
关键词
D O I
10.1021/ja045144i
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Alkylation of beta-amino ester enolates proceeds with high diastereoselectivity. Single crystal, powder, and solution X-ray diffraction studies of the enolate show that the racemic enolate forms prismatic hexamers. Li-6 NMR spectroscopic studies on partially racemic enolates reveal complex mixtures of homo- and heterochiral hexamers. An implicit fit of the aggregate populations to the Boltzmann distribution provides the free energy differences and equilibrium constants for the ensemble. Rate studies show that enolate alkylation occurs directly from the hexamer with participation by THF. A mechanism based on the alkylation of a ladder-like aggregate is proposed.
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页码:16559 / 16568
页数:10
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