Boronic Acids for Transition Metal Free Organic Synthesis

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The development of new chemical reactions for the synthesis of organic (carbon-containing) molecules plays a central role in the discovery of novel pharmaceuticals and functional materials (e.g. liquid crystals, light-emitting diodes). Past decades have seen a huge increase in such reactions involving transition-metal containing species. Although very useful, these metals have various drawbacks, including rarity (and associated high cost) and toxicity. Recently, significant attention has been paid to metal-free methods in organic synthesis, which now compete favourably in terms of efficiency with many metal-based methods without the associated disadvantages. Certain organic compounds of boron (boronic acids and their derivatives) are used commonly as reagents in metal catalysed reactions, but rarely as catalysts themselves, despite their many useful properties. These include relatively low toxicity, stability to air and moisture, low cost and their Lewis acidic nature which allows them to react in unique ways with certain substrates (Lewis bases). We have employed some of these properties to promote the so-called Friedel-Crafts reaction, which is an important process for the construction of useful molecular structures. The proposed research involves further exploitation of the unique properties of boronic acids for use as catalysts in these and other important processes, including cycloaddition (ring-forming) and rearrangement reactions. The common use of boronic acids as reagents for medicinal and materials chemistry has also prompted us to develop new methods for their preparation. We will also develop new reactions involving boronic acid derivatives as starting materials in metal free reactions. Several of these reactions lead to products where the boron group remains intact, providing synergy with existing methods for further transformation of this group. These new methods will enable the preparation of new, useful molecules that would be difficult or impossible to prepare by other means.