Dunnione and related naphthoquinones. III. Rearrangement of hydroxynaphthoquinones to indenone carboxylic acids. allodunnione

Abstract

Certain tert.-alkylhydroxynaphthoquinones are found to isomerize rapidly in hot aqueous alkali, and the reaction is correlated with the rearrangement of dunnione to allodunnione. The change also occurs, relatively slowly, with 2-hydroxy-3-isopropyl- 1,4-naphthoquinone. An alternative synthesis shows that the product in this case is 2-iaopropyl-indenone-3-carboxylic acid. The ethyl ester of this acid shows an absorption spectrum very similar to that of allodunnione. Alkaline rearrangement of 2-hydroxy-3-(1,1-dimethylallyl)-1,4-naphthoquinone evidently gives the corresponding dimethylallylindenonecarboxylic acid. Treatment of the latter with concentrated sulphuric acid forms allodunnione, and a new isomer which apparently results from a retropinacolinic rearrangement. All these observations support the structure originally proposed for allodunnione.