Chapter 8 - The Cycloheptane, Cyclo-octane and Macrocyclic Groups

Abstract

This chapter discusses tropolones and other derivatives of the quasi-aromatic cycloheptatrienylium (tropylium) cation along with cyclo-octatetraene and other annulenes, some of which show aromatic character. Methods of preparation, properties, and typical reactions of the cycloheptane, cyclo-octane, and macrocyclic group of compounds are also outlined. Derivatives of cycloheptane include: halogen compounds such as cycloheptyl chloride, alcohols and ethers such as cycloheptanol; aldehydes such as cycloheptanecarbaldehyde; ketones, hydroxyketones and diones such as cycloheptanone; carboxylic acids such as cycloheptanecarboxylic acid; and amines such as cycloheptylamine. The quasi-aromatic properties of tropolone and its parent tropone (cyclohepta-2,4,6-trienone) can be understood if these compounds are recognized as derivatives of the cycloheptatrienyl (tropylium) cation. Tropylium salts, tropone and its derivatives and analogues, hydroxytropones, tropolones, and their aza- and thia-analogues are analyzed on the basis of their formation, properties, stereochemistry, and typical reactions. The physical and chemical properties of macrocyclic compounds such as annulenes depend intimately on the conformation of the ring. The term annulene is conveniently applied to a group of compounds, which are formally monocyclic fully conjugated polyenes. Macrocyclic halides, alcohols, aldehydes, ketones, cycloalkanecarboxylic acids, and amines are the important derivatives that belong to this group and hence, their study is essential in conjunction with knowledge of conformations of macrocyclic rings.