RDA Reaction in Natural Products

The RDA reaction is often observed from steroid molecular ions, and it can be very indicative of steroidal stmcture. [107,110,113,114] The extent of the RDA reaction depends on whether the central ring junction is cis or trans. The mass spectra of A -steroidal olefins, for example, showed a marked dependence upon the stereochemistry of the A/B ring juncture, in accordance with orbital symmetry rules for a thermal concerted process. In the trans isomer the RDA is much reduced as compared to the cis isomer. The effect was shown to increase at 12 eV, and as typical for a rearrangement, the RDA reaction became more pronounced, whereas simple cleavages almost vanished. This represented the first example of such apparent symmetry control in olefinic hydrocarbons. [114]. 

The RDA reaction is also a typical process of flavones, naphthoflavones, and methoxynaphthoflavones. [115] In many cases it provides intact A- and B-ring fragments, and therefore, it is of high relevance for structure elucidation. The intensity ratio of A- to B-ring fragments was found to be strongly influenced by the substituent position, i.e., to be very sensitive to the charge distribution within the molecular ion. [116] 

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