On heating with sodium hydrogencarbonate in aqueous methanol, ailanthone (2) afforded 13 (12→11α) abeo-picrasanes [or 9 (11→12α) abeo-picrasanes], shinjudilactone (1) and its 13-epimer (3), in a ratio of 1 : 1 in good yields. The reaction is likely to proceed through isomerization of 2 into an α-diketone (6), followed by benzilic acid rearrangement. Under the same conditions, norquassin (4) gave the rearrangement product, norquassinic acid (5).
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Ishibashi et al. (1982) studied this question.