| 摘要 |
Disclosed is a method for preparing a compound of formula I, or a pharmaceutically acceptable salt thereof, comprising the steps of: (a) providing a compound of formula II (such as those obtained from plant extracts of black cohosh), and (b) converting the compound of formula II to the compound of formula I by an intramolecular dehydration reaction in the presence of a suitable acid (such as a carboxylic acid, a sulfonic acid, or a phosphoric acid); and wherein the substituents are as defined herein.
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