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Article

Concerning the Application of the ¹H NMR ABX Analysis for Assignment of Stereochemistry to Aldols Deriving from Aldehydes Lacking β-Branches

Supporting Info

Luiz C. Dias,*^§ Andrea M. Aguilar,^§ Airton G. SallesJr.,^§ Leonardo J. Steil,^§ and William R. Roush*^‡;

Instituto de Qumica, Universidade Estadual de Campinas, UNICAMP, C. P. 6154, CEP 13084-971, Campinas, SP, Brazil, and Department of Chemistry, The Scripps Research Institute, Jupiter, Florida 33458

J. Org. Chem., 2005, 70 (25), pp 10461–10465

DOI: 10.1021/jo051773e

Publication Date (Web): November 5, 2005

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

Universidade Estadual de Campinas.

‡

The Scripps Research Institute.

, ldias@iqm.unicamp.br, ; , roush@scripps.edu

Abstract

Attempts to apply the ¹H NMR ABX method for assignment of stereochemistry of β-hydroxy ketones to aldols 4−10 deriving from α-methyl aldehydes lacking β-branches reveals that the presence of a β-branch in the aldehyde reaction partner is necessary so that the average chemical environment of Ha and Hb is different for the Felkin and anti-Felkin aldols (see conformational pairs A/B and C/D, respectively). When the chiral α-methyl aldehyde lacks a β-branch, as in the case of the aldehyde precursors to 4−10, the conformational energies of E and F (for the Felkin β-hydroxy ketone derivatives), and conformers G and H for the anti-Felkin aldols, are too close in energy (within each pair), such that the average chemical and magnetic environments of Ha and Hb in the two diastereomers cannot be easily distinguished. This analysis provides a rational basis for application of the ¹H NMR ABX pattern analysis to other β-hydroxy ketone derivatives.