Platinum‐Catalysed Ring‐Opening Isomerisation of Piperidine Cyclopropanes

A range of cyclopropyl-fused N-tosyl piperidines have been synthesised and shown to undergo ring-opening isomerisation on treatment with platinum(II) catalysts. The products can have either an endo-cyclic or exo-cyclic double bond. The selectivity is influenced by reaction temperature, solvent and, most significantly, the catalyst. A mechanism involving C−C bond activation and β-hydride elimination is proposed. When β-hydride elimination is blocked, a stereospecific platinum-driven Wagner–Meerwein shift is observed.