Cyclization Reactions of the o-Naphthoquinone Diterpene Aethiopinone. A Revision of the Structure of Prionitin

Article abstract of DOI:10.1021/jo00043a034

The 4,5-seco-20(10->5)-abeo-abietane derivative aethiopinone (1), a natural o-naphthoquinone isolated from some Salvia species, was subjected to a series of acid-catalyzed reactions which yielded phenalene derivatives (2, 6, 9, and 11) and other cyclization products (3 and 10).The 11-nor derivative 3 is formed by an intramolecular <4+2> cycloaddition reaction, and a mechanistic pathway for the formation of the phenalene derivatives 6 and 11 is also proposed.These transformations of aethiopinone (1) allowed the partial syntheses of the naturally occuring diterpenes salvipisone (8), salvi lenone (9), and the racemic form of prionitin (11), a rearranged abietane diterpeniod previously isolated from the root of Salvia prionitis, to which structure 12 had been attributed only on the basis of NMR spectroscopic studies.In the light of the results reported herein, including an X-ray analysis of compound 11, the structure 12 assigned to prionitin must be changed to 11.