Photocatalytic generation of free radicals from furan

This thesis concerns the development of a stannane-free method for generating reactive free radicals adjacent to a 2,5-disubstituted furan, the development of a furan oxidation method, and the total synthesis of the legonmycins, bacterial pyrrolizidine alkaloids. The synthetic utility of free radicals, and the effectiveness of organotin compounds in generating them, are discussed in Chapter 1, as are the reasons for avoiding organotin contamination of synthetic compounds, established means for doing so, and photoredox catalysis. The synthesis of model substrates for photoredox-mediated hydrogen abstraction from 2,5-disubstituted furans is described in Chapter 2. Visible light-mediated cyclisation did not occur as intended, but the use of a polyoxometalate cluster and ultraviolet light to effect the same transformation is also described. Chapter 3 concerns the synthesis of precursors to tin-mediated generation of free radicals adjacent to furan, the behaviour of those radicals once formed, and the implications for the work described in Chapter 4. A side reaction was observed when carrying out the work described in Chapter 2; Chapter 4 describes the development of this into a method for complete and efficient conversion of furans into 2-ene-1,4-dicarbonyls, complementing existing methods for the same transformation. Chapter 5 describes abortive routes for the total synthesis of legonmycin A, via the methodology described in Chapter 4 and via nitrile activation upon acylation, and a successful route based on an existing synthesis of the jenamidines, incorporating an iodine-catalysed hydroxylation with O2 as the terminal oxidant. This transformation proved problematic in previous syntheses of similar structures.