Selective Formation of Internal Olefinic Trimer of α-Methylstyrenes with HI Gas and Ketones

[Image: see text] Reaction of α-methylstyrene in the presence of HI gas and methyl p-tolyl ketone selectively resulted in an internal olefinic trimer. We revealed that the ketones with the stabilization of the protonated state were efficient to give the corresponding trimers, whereas the other ketones gave the usual indane compound. From the investigation for the mechanistic path, we found that the trimer is a kinetic product and that indane is a thermodynamic product.