#beta#-Cyclomanganated 1,5-diphenylpenta-1,4-dien-3-ones and their reactions with alkynes: routes to #eta#~5-pyranyl- and #eta#~5-oxocycloheptadienyl--Mn(CO)_3 complexes

摘要

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-kO)]ethenyl-kC~1]tetracarbonylmanganese derivatives (5). Coupling of 5 with alkynes in some cases gives [4-phenyl-2-(2-phenylethenyl)pyranyl-#eta#~5]tricarbonylmanganese complexes (6) analogous to those previously reported for #bet#-man-ganated chalcones, but in other cases an alternative cyclisation pathway subsequent to insertion of alkyne into the C-Mn bond leads to [6-oxo-4,7-diphhenylcyclohepta-1,4-dienyl-1,2,3,4,5-#eta#]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-#eta#]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 was established by X-ray crystal structure analysis. The pyranyl complexes (6) provide the corresponding pyrylium triiodide salts (8) when demetalated with iodine.