| Abstract
| - Attempts to apply the 1H NMR ABX method for assignment of stereochemistry of β-hydroxy ketonesto aldols 4−10 deriving from α-methyl aldehydes lacking β-branches reveals that the presence ofa β-branch in the aldehyde reaction partner is necessary so that the average chemical environmentof Ha and Hb is different for the Felkin and anti-Felkin aldols (see conformational pairs A/B andC/D, respectively). When the chiral α-methyl aldehyde lacks a β-branch, as in the case of thealdehyde precursors to 4−10, the conformational energies of E and F (for the Felkin β-hydroxyketone 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 inthe two diastereomers cannot be easily distinguished. This analysis provides a rational basis forapplication of the 1H NMR ABX pattern analysis to other β-hydroxy ketone derivatives.
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