Indenols, indenones and (arylcyclohexadienyl)Mn(CO)3 π-complexes from the thermally promoted reactions of alkynes with ortho-Mn(CO)4 aryl ketone, amide, ester and aldehyde derivatives

Thermally promoted reactions of a range of alkynes with the orthomanganated acetophenone (η2-2-acetylphenyl)Mn(CO)4 generally give 1H-inden-1-ols in good yield; effects of substituents and solvent on these reactions are reported, along with the crystal structure of 1-methyl-2,3-diphenyl-1H-inden-1-ol. The corresponding orthomanganated benzophenone similarly gives the indenol with diphenylacetylene but by exception, orthomanganated 3-acetylthiophene with phenylacetylene reacts via triple alkyne insertion and cyclisation, shown by crystal structure determination of the π-complex product [(1,2,3,4,5-η)-2-(3-acetylthien-2-yl)-1,3,5-triphenylcyclohexadienyl]tricarbonylmanganese. Corresponding orthomanganated derivatives of N,N-dimethylbenzamide, methyl 3,4,5-trimethoxybenzoate and 4-dimethylaminobenzaldehyde all give indenones with diphenylacetylene, but with (excess) acetylene only the aldehyde gives an indenone, the amide and ester giving instead [(1,2,3,4,5-η)-6-arylcyclohexadienyl]Mn(CO)3 complexes. 1H NMR analysis of these complexes shows H at C6 to be on the same face of the cyclohexadienyl ring as Mn(CO)3 (endo-6-H; exo 6-aryl) as expected from three successive syn additions of alkyne at metallated carbon followed by intramolecular syn addition of alkene in the final cyclisation stage.

Alkynes normally react with orthomanganated aryl ketones to give 1H-inden-1-ols and with other orthomanganated arylcarbonyl compounds to give related cyclopentaannulation products, but in some cases triple alkyne insertion leads to (cyclohexadienyl)Mn(CO)3 complexes; the crystal structure of [(1,2,3,4,5-η)-2-(3-acetylthien-2-yl)-1,3,5-triphenylcyclohexadienyl]tricarbonylmanganese is reported.Figure optionsDownload as PowerPoint slide