Behaviour of monocomplexed 1,4-diynes in the Khand reaction and use of ethylene equivalent techniques in a convenient route to tritium-labelled methyl jasmonate

1,2-Complexed hexacarbonyl(hepta-1,4-diyne)dicobalt, obtained from hexacarbonyl(propargyl acetate)dicobalt with tri-1-butynylaluminium, has been converted, by selective Khand annulation of the complexed triple bond with vinyl benzoate, to 2-pent-2-yn-1-ylcyclopent-2-en-1-one. By use of standard procedures this alkynyl cyclopentenone has been transformed into methyl jasmonate, allowing replacement of the final hydrogenation step by tritiation to produce the labelled analogue. Two alternative approaches to the intermediate pentynylcyclopentenone were examined and shown to be unsuccessful.