Stereospecific Ion—molecule Reactions in the Trans-Decahydro-4-Hydroxyquinoline Series upon Chemical Ionization

Abstract

A series of C-2- and C-4-stereoisomeric 2-methyl-, 1,2-dimethyl- and 1-butyl-2-methyl- trans-decahydro-4-hydroxyquinolines, having a conformationally stable bicyclic system and an additional 4-substituent (chosen from ethyl, ethynyl, ethenyl, butyl and vinylethynyl), was investigated by isobutane and methane chemical ionisation (CI). It was shown that, independently of the nature of the reagent gas, the spectra of stereoisomers at C-4 differed in the intensity ratios of the [MH]+ and [MH–H2O]+ ion peaks; the latter peaks are always less intense in the case of compounds containing an axial 4-OH group. The same regularity was observed for isobutane CI followed by collision-induced dissociation and for methane CI, although the intensity ratios differ. “Approach control” was suggested to explain the observed stereospecificity of the protonation of the alcohols at the hydroxyl group. The results obtained provide a useful tool for the determination of the configuration of hydroxyl-carrying centers in other trans-decahydro-4-hydroxyquinolines and related compounds.