Unusual regioselectivity in iodoplatination of the C-C triple bond of methyl propiolate in the MeI-Pt-NaI-acetone system.

Iodide complexes of Pt in acetone solution react with an excess of CHI and the stoichiometric amount of methyl propiolate (MP) by oxidative addition of CHI and iodoplatination of the triple bond of the alkyne with the formation of [InlineMediaObject not available: see fulltext.]. The regioselectivity of iodoplatination here formally contradicts the Markovnikov rule; the Pt atom forms a σ bond with the terminal C atom of the initial alkyne. With an excess of the MP reversible iodoplatination of a second molecule of the alkyne occurs with the formation of a methyl-divinyl derivative of Pt. The addition of the second molecule of the alkyne to Pt atom occurs in accordance with the Markovnikov rule at the more electron-saturated internal carbon atom. [ABSTRACT FROM AUTHOR]