Pt(II)/SnX2 (X = Cl, Br)-Catalyzed Cyclization: Completely Different Reactivity of the Platinum Complex toward 1,6-Haloenynes and 1,6-Enynes

Using a Pt catalyst generated from PtX2, SnX2, phosphines, and H2, the cyclizations of haloenynes and enynes without a halide substituent were investigated. Under the Pt catalyst conditions, the reaction routes were partitioned into the cycloisomerization of the haloenynes and the cycloreduction of the enynes without a halogen substituent. Through the optimization of the reaction conditions and control experiments, we proposed plausible catalytic cycles to account for the bifurcation of the reaction mechanisms in addition to the demonstration of the substrate scope of the cycloisomerization of the haloenynes.