Retro-Diels-Alder fission

The fragmentation pattern of l,5-dimethyl-7-methoxy-l,2,3,4,5,10-hexahydro-4fl//-pyridazino[l,6-h]isoquinoline (22) has been studied (73JHC999). The base peak at m/e 148 might be derived through the retro Diels-Alder fission of the molecular ion. The 7-hydroxy derivative gives the same fragmentation pattern. 

Tetrahydrobenzofurans (Biemann,10 p. 106),26 like compound (31) (Biemann, loc. tit.), are easily cleaved by a retro-Diels-Alder fission,35-36 (31)- [32] ... 

The retro-Diels-Alder fission becomes very important in dihydro-fiavones and dihydroisofiavones the charge is mainly localized in the dihydro derivative of [103], Such compounds therefore exhibit very characteristic spectra. 

A new and very neat synthesis of evodiamine and rutaecarpine is described by the authors as a retro mass spectral synthesis , since the original conception was derived from the mode of fragmentation of these alkaloids in the mass spectrometer this involves a familiar retro Diels-Alder fission of ring c. Evodiamine (16a) was thus constructed by a 27r + 47r cycloaddition of 3,4-dihydro-/8-carboline with the keteneimine (17), prepared in situ by elimination of sulphur dioxide from the sulphinamide anhydride (18) (Scheme 7). When the anthranilic acid derivative (19) was used the product was rutaecarpine (20) itself, the initially formed dihydro-... 

Figure 6.15. Positive fragmentation pathways of the monomer catechin retro-Diels-Alder fission (RDA), heterocychc ring fission (HRF), benzofuran-forming fission (BFF), and loss of water molecule. (Reprinted from Li and Deinzer, 2007, Tandem Mass Spectrometry for Sequencing Proanthocyanidins, Analytical Chemistry, 79, p. 1740, with permission from American Chemical Society.)...

HCR heterocyclic ring fission, RDA retro-Diels-Alder fission... 

The mass spectrum of (6) contains,as expected, a major fragment at m/e 197. Deuteriation experiments unexpectedly show, however, that only ca. 20% of this ion originates via a retro-Diels-Alder fission of ring d instead, the ion appears to be mainly the result of a stepwise fragmentation of ring D (Scheme 4). 

The mass spectra of all adducts were characterized by the presence of a very intense ion corresponding to a retro Diels-Alder fission of the molecular ion. The isobenzofuran ion shows subsequent extrusions of CO, CHj and CHjO <83CJC1987>. Adducts of aryl isobenzofurans produce... 

FIGURE 16.4 Example of retro-Diels-Alder fission (RDA) and OC9/C2C3 cleavage. (Adapted from Delcambre, A., and Saucier, C. 2012. J. Mass Spectrom. 47 727-736. With permission.)... 

The phenanthroindolizidines give easily recognizable mass spectra owing to the intense ion at M — 69, usually the base peak, formed by loss of ring E as a pyrroline unit by a retro-Diels-Alder fission (cf. Scheme 1, for tylophorine, 13) (70). 

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