Stereospecific 1,3 and 1,4 dehydration reactions in the mass spectra of podocarpan-12- and -14-OLS†

Specific deuterium labelling revealed that podocarpan-12α- and -14α-01, representing conformationally well defined cyclohexanols, eliminate water mainly by stereospecific 1,3 reactions involving cis tertiary hydrogens on electron-impact. Dehydration of podocarpan-12ß-0l, which also involves a cis tertiary hydrogen, occurs almost exclusively by a 1,4 reaction. Subsequent decomposition of the various M – 18]⁺· ions was found to lead to different products, thus explaining some of the intensity differences encountered in the lower parts of the spectra of the epimeric podocarpan-12-ols and -14-ols.