[reaction: see text] A study of the role of base in the isomerization of manganese-coordinated conjugated alkynyl carbonyls to the corresponding allenyl carbonyls is described. The use of phosphine additives indicates that manganese requires a ligand prior to isomerization with amine bases. A series of amine bases were also examined for their efficacy in this isomerization reaction revealing a strong dependence on pK(a). By contrast, potassium tert-butoxide led to rapid isomerization in the absence of added manganese ligand.

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