Andrea Robinson Group

Homogenous Grubbs-type pre-catalysts have played an important role in the application of olefin metathesis to organic synthesis. Grafting of these homogeneous catalysts onto solid supports can aid catalyst recycling and removal of metallic residues from the product stream by filtration. In this paper we describe the reversible immobilization of a quaternary ammonium Hoveyda-Grubbs olefin metathesis pre-catalyst on sulphonic acid-functionalised silica-coated iron oxide magnetic particles. Following ring closing metathesis, the catalyst can be removed from the reaction via a magnet for reuse and/or regeneration.

Acyclic diamines are valuable feedstocks for polyamide synthesis. Ruthenium-alkylidene catalysed cross metathesis of amino alkenes is problematic and acyl derivatisation can result in less efficient syntheses, poor catalyst turnover and isomerisation. Temporary amine masking via stable and soluble ammonium salts delivers cyclic and acyclic aminoalkenes in high yield and purity.

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We have recently described synthetic routes to the azaspirocyclic ring systems found in marine tricyclic alkaloids such as Cylindricine A utilising a Ru-alkylidene cross-metathesis reaction and acid-catalysed cyclisation. Construction of the third ring, however, requires cross coupling of a highly hindered, α-substituted methylenecycloalkane. CM of such olefins is highly challenging. This paper describes a generic steric-reversal strategy that can be used to react previously unreactive, sterically demanding alkenes using commercially available catalyst.