A theoretical investigation on the mechanism of the PtCl2-mediated cycloisomerization of heteroatom-tethered 1,6-enynes

A mechanistic study based on DFT theoretical calculations for the PtCl2-catalyzed formation of bicyclic adducts from heteroatom tethered 1,6-enynes is reported. Different reaction pathways have been taken into account and the results are discussed. This analysis clearly reveals that the kinetically preferred pathway involves an initial 6-endo-cyclization from a triggered reactant complex by pi-complexation of Pt(II) onto the alkyne to form a cyclopropyl platina-carbene intermediate, followed by a [1,2]-hydrogen shift.