Mass spectral studies of some carbohydrate enones

A study of the mass spectra of ethyl 2,3-dideoxy-α-d-glycero-hex-2-enopyranosid-4-ulose1a, its 6-0-acetyl derivative1b, and methyl 3,4-dideoxy-α-d-glycero-hex-3-enopyranosidulose2a indicates that the main fragmentation of these compounds occurs by a retro-Diels-Alder type cleavage. Recognition of the ions produced by this cleavage provides a means of allocating the position of the α,β-unsaturated chromophore in carbohydrate enones. Fragmentation of molecular ions of1a and1b also occurred by direct loss of individual ring substituents to give ions which retain the pyranoid nucleus. The fragmentation pathways suggested are supported by accurate mass measurements of the salient fragment ions of1a.