New Applications of TEMPO in Organic Synthesis

This thesis contains a number of projects investigating the use of TEMPO in organic synthesis, developing new methodologies for radical reactions and synthesising new TEMPO derivatives. Chapter 1 outlines the current status quo of radical chemistry and some of the uses of TEMPO in synthesis. Chapter 2 details the TEMPO/Lewis acid mediated oxidation of acetals to form esters, in particular focussing on the optimisation of a TEMPO/MgBr2 system, examining its scope and mechanism. The TEMPO/MgBr2 system was shown to oxidise phenyl acetals with electron donating groups to form esters in moderate to good yield, but phenyl acetals with electron withdrawing groups and alkyl acetals gave considerably lower yields of esters. Chapter 3 explores the use of TEMPO as an initiator in the radical addition of diphenylphosphine sulfide to alkenes and alkynes. The scope of this reaction has been explored in the form of both simple additions to C-C unsaturated bonds and C-C bond forming reactions in the cyclisation of dienes. A mechanism for these addition reactions has been proposed. Also investigated was the addition of diphenylphosphine sulfide to Michael acceptors at room temperature in the absence of a radical initiator. The chapter includes speculation on the mechanism of the uninitiated additions. Chapter 4 discusses the synthesis of two novel nitroxide ionic liquids with the aim of using them as recyclable catalysts. The first of these, [BMIM][Carboxy-TEMPO], was synthesised in 17% yield and preliminary results show that it is capable of oxidising benzyl alcohol in [BMIM][BF4] and that both the solvent and the catalyst can be recycled. Benzyl-2-(2,2,6,6-tetramethylpiperidin-4-ylidene)acetate has been synthesised via a Horner-Wadsworth-Emmons reaction in 29% yield with aim of synthesising the second ionic liquid from it. Chapter 5 outlines efforts to use TEMPO in the chiral resolution of 1-phenylethanol with camphorsulfonate and amino acid based ionic liquids as chiral auxiliaries.