Synthesis and Reactivity of Functionalised Triarylphosphines in Organic Synthesis

Abstract

The goal of this research was to develop alternate economic routes for the synthesis of functionalised triarylphosphines. Such species are employed as catalysts ligands in chemical synthesis and can be incorporated into designed-ylides for olefination reactions. The synthesis of the SHOP ligand, the key constituent of the Shell Higher Olefins Process for making linear alpha olefins via ethylene oligomerisation and olefin metathesis, is described using four totally new approaches. These include a Directed Ortho Metalation (DOM) approach, Copper iodide catalyzed cross-coupling, Halogen-Magnesium Exchange reaction and Diazonium salt approaches. The efficiency, in terms of overall yield and mild process conditions, make some of the routes potentially commercialisable. Additionally, a series of ortho-substitued triarylphosphines were derived to probe and modulate the reactivity of the Wittig reaction. We report that non-stabilized ortho-P-alkoxy-substituted ylides react with aromatic and aliphatic aldehydes providing (E)-olefins with high stereocontrol employing an intramolecular phenoxy and alkoxy substituent to promote (E)-olefination through betaine interconversion. In one particular case; removal of phosphoine oxide was also achieved. Extension of this methodology was also carried out on semi-stabilized benzylic ylides, which are known for producing 1:1 mixtures of (E):(Z) olefins under classical condition. Potential applications of the methodology are also described.