Chapter 2 - The Cyclopropane Group

Abstract

Publisher Summary This chapter reviews several new approaches to the construction of the three-membered ring. New synthetic methods for individual compounds and preparative methods which utilize cyclopropane precursors are discussed. A variety of cyclopropane compounds may now be synthesized by the use of sulfonium ylids, which have been developed into extremely versatile and useful reagents for this purpose. Cyclopropanes have been formed by the methylenation of olefins by treatment with methylene halide and an organolithium reagent. Yields are modest but the reaction is of importance theoretically. Cyclopropenes are formed by photolysis of the sodium salts of the tosylhydrazones of α,β-unsaturated ketones. Protonated cyclopropanes have been implicated as intermediates in reactions on cyclopropyl substrates, when treated with acidic or electrophilic reagents and also on open-chain substrates, such as 1-amino-, 1-chloro-, or 1-hydroxy-propane. The cyclopropane ring can transmit, as well as extend, the conjugation of contiguous unsaturated groups. This property has been confirmed by nuclear magnetic resonance studies on 1-aryl-2-benzoylcyclopropanes and on fluorine-substituted 1,2-diarylcyclopropanes, by Raman studies on 1-aryl-2-vinylcyclopropanes, and also by chemical evidence.