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

Comparison of the room- and low-temperature H-1 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 Delta delta(T1T2) for substituents R-1/R-2, 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 H-1 NMR spectra, and calculation of the Delta delta(RS) signs for the methines H alpha(R-1) and H alpha(R-2) and R-1/R-2 protons. The reliability of these correlations is validated with 17 diols of known absolute configuration used as model compounds.