Chiral silylation reagents: Determining configuration via NMR-spectroscopic coanalysis

Derivatization with (+)- and (-)-chloromenthoxydiphenylsilane was used to determine the absolute configuration of the insect defensive agent pinoresinol (1). Although the H-1 NMR chemical shift differences of the resulting two diastereomers are small, H-1 NMR spectroscopy provided for the unambiguous assignment of the natural product's configuration. For this purpose, a new approach involving NMR spectra of mixtures of diastereomers was used. Our method resembles coinjecting mixtures of samples of known and unknown configuration in GC and HPLC.