AN APPROACH TO THE SYNTHESIS OF STIPITATIC ACID

Abstract

An approach to the synthesis of the penicilium mold metabolite stipitatic acid has been investigated. It involved the preparation of a bis-(alpha)-diazoketone derived from citric acid, whose central (alpha)-hydroxy acid function had been masked and protected, and its conversion into a 6,6-disubstituted 2-cycloheptene-1,4-dione by intramolecular diazoketone coupling catalyzed by bis-cyclopentadienylnickel (nickelocene). Bromination of the enedione, followed by dehydrobromination, yielded a bromoenedione. (beta)-Elimination of both enediones with potassium hydroxide gave (gamma)-tropolones. Alakali treatment of the bromotropolone afforded a phenolic ring contraction product.