Preparation of cyclomanganated chalcones and their reactions with methyl acrylate and other α, β-unsaturated carbonyl compounds

Article abstract of DOI:10.1016/0022-328X(95)05488-B

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-κC¹>tetracarbonylmanganese, while the second type, manganated at the aryl ring ortho-carbon, are derivatives of <2-<3-phenylprop-2-en-1-onyl-κO>phenyl-κC¹>tetracarbonylmanganese.In general, more "alkene-manganed" than "ring-manganated" product is formed, with the ratio influenced significantly by certain substituents, e.g. a 4-CF3 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-((1S^*, 2R^*, 3S^*)-1-hydroxy-1-((E)-2-(2-trifluoromethylphenyl)ethenyl)-3-(2-trifluoromethylphenyl)-6-methoxy-2-indanylcarbonyl-κO)-6-methoxyphenyl-κC¹>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-κC¹>tetracarbonylmanganese to form the cyclized product 5-acetyl-1-(4-chlorophenyl)-3-(3,4,5-trimethoxyphenyl)cyclopent-2-en-1-ol.Keywords: Manganese; Alkene; Chalcones; Crystal structure; Cyclometallation; Metallacycle