Allenes bearing a pro-nucleophile can be cyclized on treatment with a wide variety of transition metal catalysts and reagents: palladium, cobalt, ruthenium, silver, rhodium, lanthanides, gold. The nucleophilic groups can be nitrogen, oxygen or carbon based and can form rings of various sizes, often with good control of stereochemistry. A variety of mechanisms can be proposed for these reactions and the metal complex can be used to introduce a variety of functional groups during cyclization. Several heterocyclic natural products have been prepared using a selection of these reactions.

[reaction: see text] Ring-closing metathesis (RCM) of vinyl fluoride-containing dienes in the presence of ruthenium alkylidene carbene complex 11 proceeded efficiently to give six- and seven-membered cyclic vinyl fluorides. The RCM reaction was used to prepare amine- and sulfamide-linked cyclo-olefins, as well as carbocyclic systems, from a simple commercial fluoro-olefin.

An enantioselective synthesis of (-)-galanthamine has been realized in 11 linear steps starting from isovanillin. A Mitsunobu aryl ether forming reaction was used to assemble the galanthamine backbone, which was stitched together using enyne ring-closing metathesis, Heck, and N-alkylation reactions affording the tetracyclic ring system. Control of relative and absolute stereochemistry was derived from an easily accessible enantiomerically enriched propargylic alcohol 13.