PtBr2-catalyzed transformation of allyl(o-ethynylaryl)carbinol derivatives into functionalized indenes. Formal sp3 C-H bond activation

The PtBr2-catalyzed reaction of 1-ethynyl-2-(1-alkoxybut-3-enyl)benzenes at 120 degrees C in CH3CN gave functionalized indenes in good to allowable yields. Most probably, the hydrogen at the terminal alkyne is transferred to the adjacent internal beta-carbon to form an (eta2-vinylidene)platinum carbene intermediate, which activates the sp3 C-H bond at the benzylic carbon. This reaction pathway is supported by DFT calculations which suggest that the formation of the Pt-vinylidene complex is the rate-limiting stage for the whole transformation.