Platinum‐Catalysed Ring‐Opening Isomerisation of Piperidine Cyclopropanes

Abstract

Ar ange of cyclopropyl-fused N-tosyl piperidines have been synthesised ands hown 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, solventa nd, most significantly,t he catalyst. Am echanism in-volvingC ÀCb ond activation and b-hydride eliminationi s proposed. When b-hydride elimination is blocked, as tereospecific platinum-driven Wagner-Meerwein shift is observed.

Diversity-Oriented Synthesis toward Fused and Bridged Benzobicyclic Piperidin(on)es

“…Another attractive case is the transformation of 2-azabicyclo[4.1.0]­heptanes into cyclopentane-fused piperidines by intermolecular [3 + 2] cycloaddition with olefins (Scheme , eq 4) and the observation that salt of isomer endo of 7-chloro-2-azabicyclo[4.1.0]­heptane could be converted to ring-expanded tetrahydroazepine under reductive amination conditions (Scheme , eq 5) . Quite recently, the transformation of N–Ts 2-azabicyclo[4.1.0]­heptane to the piperidine ring with an endo- or exo-cyclic double bond via the ring-opening isomerization process has also been reported (Scheme , eq 6) …”