1,5-Diphenylpenta-1,4-dien-3-ones ( 4) are cyclometalated with benzylpentacarbonylmanganese to form [[1-phenyl-2-(( E)-3-phenylprop-2-en-1-oyl-κ O)]ethenyl-κ C 1]tetracarbonylmanganese derivatives ( 5). Coupling of 5 with alkynes in some cases gives [4-phenyl-2-(2-phenylethenyl)pyranyl-η 5]tricarbonylmanganese complexes ( 6) analogous to those previously reported for β-manganated chalcones, but in other cases an alternative cyclisation pathway subsequent to insertion of alkyne into the CMn bond leads to [6-oxo-4,7-diphenylcyclohepta-1,4-dienyl-1,2,3,4,5-η]tricarbonylmanganese complexes ( 7). The X-ray crystal structure determination is reported for one such compound, [6-oxo-2,4,7-triphenylcyclohepta-1,4-dienyl-1,2,3,4,5-η]tricarbonylmanganese ( 7a), derived from 1,5-diphenylpenta-1,4-dien-3-one and phenylacetylene. The 7-phenyl group is found to occupy the endo position, and a mechanism involving Mn-mediated aryl migration is suggested to explain this stereochemistry. The reaction of 7a with ammonium cerium(IV) nitrate gives a low yield of 2-nitro-3,5,7-triphenylcyclohepta-2,4,6-trien-1-one ( 9), whose structure was established by X-ray crystal structure analysis. The pyranyl complexes ( 6) provide the corresponding pyrylium triiodide salts ( 8) when demetalated with iodine.