The spirodienone route for the functionalization of calixarenes

Mild oxidation of calixarenes affords their spirodienone derivatives. These derivatives are useful synthetic intermediates for the selective functionalization of calixarenes. The presence of several functionalities (carbonyl, ether, diene) within the calix scaffold enables them to undergo a large number of synthetic transformations. The spirodienone calixarene derivatives have been utilized for the selective derivatization of two vicinal OH groups, the replacement of one or two OH groups, the formation of Ar-O-Ar bonds between neighboring aryl groups, the functionalization of the calix scaffold at the extraannular positions (via spirodienol derivatives), and the modification of the methylene groups. 1. Introduction 2. Spirodienone Calixarene Derivatives 3. Isomerism and Mutual Interconversion 4. Spirodienone Derivatives of Larger Calixarenes 5. Synthetic Applications of Spirodienone Calixarene Derivatives 5.1. Spirodienones as Protecting Groups 5.2. Selective Aminodehydroxylation of Calixarenes 5.3. Replacement of Two OH Groups by Methyls 5.4. Dehydration of Two Proximal Phenol Groups 5.5. Extraannular Modification of the Calix Scaffold: Spirodienol Calixarene Derivatives 5.6. The Spirodienone Route for Methylene Functionalization 6. Conclusions.