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Relative and absolute stereochemistry of secondary/secondary diols: low-temperature 1H NMR of their bis-MPA esters.

Freire F, Calderón F, Seco JM, Fernandez-Mayoralas A, Quiñoá E, Riguera R

Departamento de Química Orgánica, Facultad de Química, and Unidad de RMN de Biomoléculas Asociada al CSIC, Universidad de Santiago de Compostela, 15782, Santiago de Compostela, Spain.

Comparison of the room- and low-temperature 1H NMR spectra of the bis-(R)- or bis-(S)-MPA ester derivative of an open chain sec,sec-1,2-diol allows the easy determination of its relative stereochemistry and in some cases absolute configuration. If the diol is anti, its absolute configuration can be directly deduced from the signs of DeltadeltaT1T2 for substituents R1/R2, but if the relative stereochemistry of the diol is syn, the assignment of its absolute configuration requires the preparation of two derivatives (both the bis-(R)- and bis-(S)-MPA esters), comparison of their room-temperature 1H NMR spectra, and calculation of the DeltadeltaRS signs for the methines Halpha(R1) and Halpha(R2) and R1/R2 protons. The reliability of these correlations is validated with 17 diols of known absolute configuration used as model compounds.

Published 23 March 2007 in J Org Chem, 72(7): 2297-301.
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