Journal of the Chemical Society. Perkin transactions II p. 373 - 382 (1984)
Update date:2022-09-26
Topics:
Waring, Anthony J.
The well known rearrangements of α-santonin (2) to α-desmotroposantonin (3) in aqueous sulphuric acid, and to its acetate in acetic anhydride, have been reinvestigated.No evidence was found for the formation of isomeric products apart from the known β-desmotroposantonin (4).Kinetic and basicity measurements, allied to the use of acidity functions, allow the conclusion that, in >45percent H2SO4, α-santonin (2) rearranges slowly to trans-desmotroposantonin, which rapidly epimerises to (3).In more dilute acid there is evidence of a change in mechanism.The cation of 6-epi-α-santonin (5) rearranges about 1 000 times faster than those of α-santonin and a number of analogues, including the lactone-free analogue (6).This is attributed to a favourable interaction between the lactone ring of (5) and the dienone ring over which it can be closely folded.
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