Alkenylcuprates or allenolates–that is the question! The structures of the adducts formed by addition of cuprates to ynones and ynoates has been a matter of controversy for several decades. New NMR spectroscopic investigations with 13C-labeled substrates now reveal that there is no simple answer to the question. Some reactants give alkenylcuprates 1, others allenolates 2 as the most stable adducts. The transformations can be regarded as carbocupration of an alkyne rather than a Michael addition.
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Nilsson et al. (1998) studied this question.