Abstract The carbonyldicobalt-mediated alkyne/allene/CO cocyclization gives 4- alkylidenecyclopentenones as the major [2+ 2+ 1] cycloadducts. The regio-and stereoselectivities depend mainly on the substitution pattern of both the alkyne and the allenic moieties, which can be rationalized using the Magnus mechanism. However, contrary to this model, and in agreement with more recent mechanistic studies, our results ...
