Ni(COD)(2): an efficient promoter in the construction of 5-cyclopent-2-enone derivatives from allyl halides, alkynes and carbon monoxide

Cyclopentenone derivatives are obtained from alkynes, allyl halides and car bon monoxide in a single synthetic operation by the use of Ni(COD)(2) with minimal formation (if any) of Ni(CO)(4). The initial formation of a pi-ally l nickel complex, first intermediate in the so far postulated mechanism, is a Valid pathway to the three component cycloaddition. However, care should be taken to minimize the side reactions in the process, the extension of w hich depends on the nature of both the alkyne and the allyl derivatives. Re liable monitoring of the components throughout the process results in good yields of the cycloadducts. (C) 1999 Elsevier Science S.A. All rights reser ved.