New Directions in Borrowing Hydrogen Catalysis

Catalysis is most simply described as the ability of a small amount of a substance to accelerate the rate of a reaction. This is an extremely useful process and has found applications throughout the modern world. For instance, a catalytic converter in a car's exhaust system utilises a catalyst to convert harmful gases like carbon monoxide into the less harmful carbon dioxide. Many of the catalysts that are most commonly used throughout industry are based on metals, some of which are expensive due to limited amounts present in the earth's crust and/or high mining and recycling costs.

Over the last 15 years there has been an explosion of interest in the field of organocatalysis, where the focus is on using a small amount of an organic molecule to accelerate the rate of reactions. As developments in this area have continued, organocatalysis has emerged as an attractive alternative to some traditionally metal-catalysed processes both in academic and industrial circles. Typically, organocatalysts are highly stable towards moisture and oxygen, readily available using sustainable natural resources, low cost and have low associated toxicity. As a result of these characteristics and the vast body of research that has been performed in the field over the past 15 years, organocatalysis is now established as the 3rd major branch of catalysis alongside transition metal catalysis and bio-catalysis. Furthermore, asymmetric organocatalytic methods, where one enantiomer (left handedness) is preferentially formed over the other (right handedness) have advanced to a level where selectivities of 99:1 are commonplace.

Within the academic research community, we now find ourselves in the privileged position that a vast array of powerful organic, metal and bio-catalysts exist, with much of their associated reactivity and behaviours well understood. These catalysts are extensively being used to carry out exciting and diverse chemical reactions, producing valuable products in cheaper, more efficient ways. An opportunity now exists to apply the knowledge of how distinct catalysts operate and develop new systems that employ multiple compatible catalysts. If these multi-catalytic systems are correctly designed the potential is vast for the development of highly efficient, "greener" chemical processes that can carry out multiple chemical steps in one single operation, representing progress towards more sustainable chemistry.

Cognisant of the outlined benefits, this work aims to combine the power of transition metal catalysis with asymmetric organocatalysis. More specifically, organometallic borrowing hydrogen complexes will be employed in tandem with organocatalysts, allowing various organocatalytic processes to be performed using inexpensive and tractable alcohol starting materials. This novel methodology will allow a highly streamlined and efficient access to valuable stereodefined building blocks that will be applied towards the synthesis of small biologically active natural products and pharmaceuticals. Research in this area will represent progress towards the more sustainable synthesis of chiral building blocks that can be immediately integrated into discovery chemistry, where rapid synthesis of non-planar molecules is essential in library preparation.