MASS SPECTRA OF BIS-1,3-DITHIOLANES AND BIS-1,3-DITHIANES . MECHANISM OF RING-CLEAVAGE REACTIONS OF MALONALDEHYDE BISTHIOACETALS AND STRUCTURES OF GLYOXAL BISTHIOACETALS

α cleavage and two ring-cleavage reactions constitute the major fragmentation pathways of malonaldehyde bisthioacetals. The mechanisms of the ring-cleavage reactions have been elucidated and one of them has been shown to proceed with McLafferty rearrangement of the angular hydrogen of the distal ring to the departing chain of the fragmenting ring, α cleavage is the only major fragmentation reaction of glyoxal bisthioacetals and biacetyl bisthioketals, establishing the pendant rather than the fused bicyclic systems as the correct structures of these compounds. © 1969, American Chemical Society. All rights reserved.