Mass spectrometry in structural and stereochemical problems—CLXXXVII A study of skeletal rearrangements in chromans by combined 13C and deuterium labeling

Chroman (I), 2,2-dimethylchroman (II), flavan (III) and 2,2-diphenylchroman (IV) were labeled with ¹³C or deuterium at every position of importance. The mass spectra of these labeled compounds make possible a detailed interpretation of some very complex carbon skeleton rearrangements. The combination of deuterium and ¹³C-labeling revealed that loss of CH₃, C₂H₅ and C₇H₇ fragments from chroman (I), 2,2-dimethylchroman (II) and 2,2-diphenylchroman (IV) respectively, occurs by multiple pathways involving aryl or alkyl migrations with little hydrogen randomization prior to fragmentation. Although ejection of C₇H₇ from flavan (III) occurs to a small extent by a route similar to those mentioned above, its [M ? C₇H₇] fragment can also be formed by a pathway involving no phenyl migration but extensive hydrogen scrambling. The validity of the schemes proposed on the basis of the ¹³C labeling data was checked by using them to predict the spectra of the deuterium labeled compounds.