Routes to Xanthones: An Update on the Synthetic Approaches

Xanthones belong to a class of O-heterocycles which are known for their great variety of biological/pharmacological activities. The xanthone scaffold can be considered as a privileged structure and for that reason it is an excellent starting point for the search of new bioactive molecules. This review intends not only to make a literature survey about the synthesis of xanthones, but also to organize the most important and common syntheses that have been published from 2005 to 2012 in an integrative way. Among the new developed approaches, we highlight the synthesis of xanthones via benzyne, palladium-catalyzed, domino type reactions and imidazolidenyl carbene-catalyzed reactions. In the first three sections it is given an overview about the classic synthetic approaches, focusing on recent developments; the fourth section orders different approaches described for the synthesis of xanthones using chromen-4-ones as building blocks. As far as our knowledge, this is the first time that a review systematizes the synthesis of xanthones based on chromen-4-ones. The fifth section refers to a miscellaneous of synthetic approaches that do not fit in any of the previous but nevertheless are useful. The last section is devoted to molecular modifications that can be done directly from the xanthone scaffold.