Die massenspektrometrische retro‐Diels‐Alder ‐Reaktion: 1, 2, 3, 4‐Tetrahydroisochinolin und 1, 2, 3, 4‐Tetrahydronaphthalin (Tetralin). 31. Mitteilung über massenspektrometrische Untersuchungen

The Mass Spectral retro‐Diels‐Alder ‐Reaction: 1,2,3,4‐Tetrahydroisoquinoline and 1,2,3,4‐Tetrahydronaphthaline (Tetraline) The retro‐Diels‐Alder reaction of 1,2,3,4‐tetrahydroisoquinoline and of its N ‐acetyl derivative was confirmed on the basis of labelled derivatives (Scheme 2) . Furthermore, the loss of ethylene was investigated with the 1,2,3,4‐tetrahydronaphthalene‐ and 1,2,3,4‐tetrahydronaphthalen‐1‐one‐derivatives given in Schemes 4 , 5 and 6. In the case of the 1,2,3,4‐tetrahydronaphthalen‐1‐one‐derivatives ethylene is lost via a retro‐Diels‐Alder reaction. The loss of ethylene from 1,2,3,4‐tetrahydronaphthalene ( 1 ) and from its derivatives is a rather complex reaction ( Scheme 8 ): 1/3 of ethylene is split off 1 + via a formal retro‐Diels‐Alder reaction, 2/3 are lost after a specific rearrangement. The ratio of these two fragmentation pathways depends very much on the substituents placed at the aliphatic and the aromatic rings, compare e.g. Table 4 .