Chapter 26 - Benzocyclopropene, benzocyclobutene and indene, and their derivatives

Abstract

Ab initio calculations of ring strain in benzocyclopropenes, benzoyclobutene, and indene indicate that these are 52.6, 28.4, and 5.9 kcal/moles respectively. Ring strain in the two former hydrocarbons leads to characteristic reactions involving opening of the small fused ring this is not generally evident for indene and its derivatives. The high strain and associated high energy available in benzocyclopropene and its derivatives possesses unusual chemical properties which are of theoretical as well as synthetic importance. The reactions involving opening of the cyclopropane ring presents the occurrence of the cleavage of the cyclopropane ring to benzyl compounds. The NMR spectrum shows that this compound is aromatic, and its structure is confirmed by an X-ray study. The other reactions of benzocyclopropenes are presented with schematic diagrams and structures. Organometallic derivatives of the benzocyclobutenes are the subject of much work during the last decade. The compounds of cyclopentabenzene and the compound with the partially saturated five-membered ring also known as indene are considered in this chapter. The chemistry involving the indene compounds is presented in the chapter.