Development of Radical Cascade via Gold(I) Photocatalysis and Application towards One-Pot Bromination/Carbocyclization

Abstract

Radical chemistry is a crucial tool to organic chemists. Recent trends in the field have been directed towards the development of photocatalysts capable of generating a radical through a renewable source like sunlight using a single electron transfer mechanism. The use of Au2dppm2Cl2, having a stronger reducing potential, allows an expansion of the reactivity to those achieved by iridium and ruthenium catalysts.1 The focus of this thesis is axed on the development of Au2dppm2Cl2 as an efficient photoredox catalyst for a tandem one-pot catalysis and its application in a dual catalytic system. The use of Au2dppm2Cl2 in a dual catalysis for the synthesis of β-amino acids was undertaken. The problems encountered over the course of the investigation showed an insufficient oxidation potential of the photoredox catalyst in addition to the facile homolytic cleavage of the C-halogen bond under UV light. However, this shows great promise for the achievement of beta amino acids using solely organocatalysis. The development of a tandem one-pot radical cyclization for the synthesis of fused- carbocycles, which are frequently encountered scaffolds in diterpenoid natural products, is reported. The initial experiments were conducted on a model substrate, enabling the verification of the proposed hypothesis. The success of this methodology was then applied to various substrates affording the desired fused 5 membered rings in good yields. These reactions show tremendous potential in the field of total synthesis for the rapid access of complex molecular structures. (1) Revol, G.; McCallum, T.; Morin, M.; Gagosz, F.; Barriault, L. Angew. Chem. Int. Ed. 2013, 52, 13342.