Chalcones [( E)-1,3-diarylprop-2-en-1-ones] react with benzyltetracarbonylmanganese under reflux in petroleum spirit to give two types of cyclomanganation products. The first, involving metallation at the alkenyl β-carbon of the enone, are derivatives of [[1-phenyl-2-phenylcarbonyl- κO]ethenyl- κC 1]tetracarbonylmanganese, while the second type, manganated at the aryl ring ortho-carbon, are derivatives of [2-[3-phenylprop-2-en-1-onyl- κO]phenyl- κC 1]tetracarbonylmanganese. In general, more “alkene-manganated” than “ring-manganated” product is formed, with the ratio influenced significantly by certain substituents, e.g. a 4-CF 3 substituent on the phenyl ring at C3 of the enone strongly promotes “alkene-manganation”. In some cases there are minor by-products derived from coupling of two chalcone molecules after initial cyclomanganation. The crystal structures are reported for two such products, [2-((1 S ∗, 2 R ∗, 3 S ∗)-1- hydroxy-1-((E)-2-(2- trifluoromethylphenyl)ethenyl)-3-(2- trifluoromethylphenyl)-6- methoxy-2- indanylcarbonyl-κO)-6- methoxyphenyl-κC 1] tetracarbonylmanganese and (1S ∗, 4S ∗, 5R ∗)-5-(4-bromobenzoyl)-1-(4-bromophenyl)-3,4-di-(4-trifluoromethylphenyl)cyclopent-2-en-1-ol. In acetonitrile under reflux, alkene-manganated chalcones react with methyl acrylate (methyl propenoate) to form derivatives of methyl ( E)-4,6-diphenyl-6-oxohex-2-enoate and of 5-(2-methoxycarbonylethyl)-3,5-diphenylfuran-2(5H)-one. The latter butenolides are not formed when the reactions are carried out in carbon tetrachloride, only the former α, β-unsaturated esters. By contrast, in a few reactions studied, acrolein (propenal) and methyl vinyl ketone (but-3-en-2-one) give only the butenolide products when treated with alkene-manganated chalcones in refluxing acetonitrile. An exception is the reaction of methyl vinyl ketone with [[1-(3,4,5-trimethoxyphenyl)-2-(4-chlorophenylcarbonyl- κO)]ethenyl- κC 1]tetracarbonylmanganese to form the cyclized product 5-acetyl-1-(4-chlorophenyl)-3-(3,4,5-trimethoxyphenyl)cyclopent-2-en-1-ol.