Titanocene catalysed 5-exo cyclisations of unsaturated epoxides-reagent control in radical chemistry

A synthetic route to carbocyclic and heterocyclic [3.3.0], [4.3.0] and [5.3.0] systems containing pyrrolidine and tetrahydrofuran units and various other tetrahydrofuran derivatives is presented. The products are of relevance for natural product synthesis and for the synthesis of biologically active compounds. The titanocene catalysed reactions utilises readily available unsaturated epoxides as substrates. A model explaining the diastereoselectivity of cyclisation is presented that should allow for rational design of more selective catalysts.