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.

Mass Spectrometry in Russia

“…Similar "approach control" was suggested to explain the stereospecificity of the protonation of tertiary alcohols in the transdecahydro-4-hydroxyquionoline series. 68,69 It has been also demonstrated that CI mass spectrometry can be used for the determination of the configuration of the chiral C-4 center in 2,6-diaryl-substituted pyperidin-4-ol silyl ethers. 70 For the investigation of stereospecificity of EI-induced fragmentation, methyl(trideuteromethyl) esters of substituted 6-phenylcyclohex-3-ene-carboxylic acids have been synthesized directly in a GC column of a GC/MS system by successive introduction of acids and CH 3 OH(CD 3 OH)/BF 3 -etherate.…”

Stereospecific Ion—Molecule Reactions of Anabolic-Type Steroid Tertiary Alcohols with Proton-Donating Cations

“…The shielding effect of the bulky methyl group in 2methylcyclopentanols was suggested to explain the difference in the ease of dehydrogenation of cis-and trans-isomers in isobutane or ammonia plasma. 18 In our recent work, 19 steric hindrance to the attack of a proton-donating cation from the axial region was involved to explain the easier dehydration of the protonated equatorial OH group vs the axial group in the case of conformationally rather stable 4alkyl-4-hydroxy-trans-decahydroquinolines.…”