Terpenoids. Part 9. 10α→ 9α-Methyl migration in derivatives of grandiflorenic acid
Abstract
Attempts to rearrange grandiflorenic acid [ent-kaura-9(11),16-dien-19-oic acid] to rings C/D analogues of antheridiogen (AAn) were unsuccessful. The norketones of grandiflorenic acid and the methyl ester underwent 10α→ 9α-methyl migration when treated with acetyl hypobromite, aqueous sulphuric acid, and bromine.