The mass-spectral fragmentation behavior of 6-keto steroids has been studied in detail by examining the mass spectra of various deuterated and C-3 substituted cholestan-6-ones. Special emphasis has been placed on elucidating the course of the reaction associated with the loss of carbon atoms 1, 2, 3, and 4 of ring A less one hydrogen atom. This hydrogen transfer was found to be remarkably stereospecific, approximately 40% arising from the 3α- and the remainder from the 2α-position. A mechanism is proposed to account for this stereospecificity and for the observation that the intensity of the peak under consideration varies greatly depending upon the experimental conditions. In connection with a description of the syntheses of the various deuterated analogs of cholestan-6-one attention is called to the unexpectedly strong inhibitory influence of a 6β-substituent upon the extent of base-catalyzed deuterium exchange in the corresponding 3-ketone.
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Djerassi et al. (1965) studied this question.