Change of the reaction pattern by methodological variations in a multicomponent assembly promoted by Ni complexes

The pi -allylnickel complex formed by the addition of trimethylsilyl chlori de (TMSCl) to a mixture of [Ni(cod)(2)] (cod = 1,5-cyclooctadiene) and a vi nyl ketone (Mackenzie complex) carbometalates an acetylene in a completely regioselective manner resulting in the formation of the corresponding vinyl nickel species. This intermediate is capable of controlled quenching in a variety of ways to give different types of compounds: under a CO atmosphere , an acylnickel species is formed that ensues from the carbometalation of t he enol ether double bond to form cyclopentenone derivatives. Alternatively , if acetylene is present in excess and CO is absent, another acetylene moi ety will replace the CO and cyclohexadienes will result instead. Finally, i f only an excess of the vinyl ketone is used, the product from a slow doubl e addition of the vinyl ketone across the triple bond is formed. The regios electivities obtained by the present method are different from those obtain ed by the involvement of nickel acyclopentadienes as intermediates when the order of addition is reversed.