Discrimination of remote chirality of primary alcohols using 1,1′-binaphthyl-2,2′-DIYL phosphoroselenoyl chlorides as a chiral molecular tool
The reaction of trichlorophosphine, 1,1′-binaphthyl-2,2′-diols with various substituents at the 3,3′-positions, and elemental selenium in the presence of Et3N gave phosphoroselenoyl chlorides in low to high yields depending on the substituents on the binaphthols. To evaluate their utility as chiral derivatizing agents of primary alcohols having a chiral center β to the hydroxy group, the obtained chlorides were reacted with alcohols to yield phosphoroselenoic acid esters. 31P and 77Se NMR spectra of some esters with an unsubstituted binaphthyl group showed two signals corresponding to their diastereomers. Among them, the diastereomers of alcohols with chiral quaternary centers were clearly distinguished in the NMR spectra. This discrimination was further improved by the use of esters having binaphthyl groups with substituents at the 3,3′-positions. In particular, the signals due to the diastereomers of esters having binaphthyl groups with C6H4C6H3Me2-3,5 and SiiPr3 groups were more clearly separated in NMR spectra. Sequential recrystallization of the esters derived from primary alcohols having quaternary carbon centers gave only one of the diastereomers. Their molecular structures were determined by X-ray analyses.
