Intramolecular five-membered ring compounds and their applications

Bäller and Müller reported the first intramolecular five-membered ring with a main group element in 1955 when they synthesized an organoaluminium compound. These five-membered ring compounds are very easily and selectively synthesized when compared with other compounds containing four-, six- and seven-membered rings. Many such compounds, especially, organotransition metal compounds have been isolated by cyclometalation since the 1970s with a wide variety of metals. These organometallic compounds are highly reactive and are also used as high turn over catalysts in dehydrogenation and metal-catalyzed cross-coupling reactions. They are useful in organic syntheses such as alkenylation, alkynylation, acylation, carbonylation, halogenation, reactions with isocyanates, thermal degradations, reactions of chiral compounds with amino acids, enantioselective rearrangements and asymmetric Diels–Alder reactions.