Level 1 – Case 4
26
In Summary
The nature of the Lewis acid is determinant in the control of the diastereoselectivity of the hydride reductions of E-ketoesters 1. Strongly chelating TiCl 4 leads
mainly to the syn-alcohol 2 with BH 3 ·py as the reducing agent, while the antiisomer 3 is obtained in preference during the reduction of 1 with CeCl 3 /LiEt 3 BH.
The differences in the chelating ability of the metal can explain the reversed
stereochemistry observed in the reaction.
Additional Comments
This problem is based on the work by Marcantoni E, Alessandrini S, Malavolta M,
Bartoni G, Belluci MC, Sambri L, Dalpozzo R (1999) J. Org. Chem. 64:19861992.
Subjects of Revision
Models for the diastereoselectivity of additions to C=O groups. Parameters of solvent polarity.
26
In Summary
The nature of the Lewis acid is determinant in the control of the diastereoselectivity of the hydride reductions of E-ketoesters 1. Strongly chelating TiCl 4 leads
mainly to the syn-alcohol 2 with BH 3 ·py as the reducing agent, while the antiisomer 3 is obtained in preference during the reduction of 1 with CeCl 3 /LiEt 3 BH.
The differences in the chelating ability of the metal can explain the reversed
stereochemistry observed in the reaction.
Additional Comments
This problem is based on the work by Marcantoni E, Alessandrini S, Malavolta M,
Bartoni G, Belluci MC, Sambri L, Dalpozzo R (1999) J. Org. Chem. 64:19861992.
Subjects of Revision
Models for the diastereoselectivity of additions to C=O groups. Parameters of solvent polarity.