Direct Alkene and Alkyne Borylation with Borenium Cations

点击翻译按钮获取中文摘要

Organic molecules containing boron substituents are widespread intermediates in the synthesis of new molecules for drug discovery, agrochemicals and organic electronics. This ubiquity arises from their high efficacy in a range of functional group transformations, particularly those involving the formation of new C-X bonds (X = carbon, nitrogen, oxygen). The combination of this efficacy with the stability and ease of handling of common boron containing compounds explains their extraordinary popularity amongst synthetic chemists. However, the installation of a boron group onto an organic molecule (termed borylation) has historically proceeded by inefficient processes, often requiring numerous steps, undesirable intermediates, highly reactive reagents and cryogenic conditions. A new generation of borylation methodologies has improved this situation somewhat, but these approaches require either halogenated intermediates, expensive transition metal catalysts or cannot be applied to certain important families of compounds. Thus the development of fundamentally new borylation methodologies for unsaturated organic molecules, e.g., alkenes and alkynes that proceeds in one step without requiring toxic precious metal catalysts and cryogenic conditions would be extremely valuable.We have recently shown that cyclic organic molecules (arenes) can be borylated using three coordinate cationic boron compounds, termed borenium cations. This process takes place rapidly and with high selectivity at ambient temperature using inexpensive and readily synthesised borenium cations. Importantly this process occurs in one-step without precious metals and is applicable to classes of compounds other modern methodologies struggle with. This proposal will extend this breakthrough by using borenium cations to borylate a wide range of alkynes and alkenes. These acyclic compounds will react in an analogous manner to arenes allowing for the direct conversion of a C-H bond into a C-B bond facilely generating the valuable borylated organic product. By subtle modification of the borenium cation we will also sequentially add a boron and a hydrogen substituent to an alkene or alkyne (termed hydroboration). Classic hydroboration routes involved the simultaneous addition of B and H which results in a certain product geometry. The borenium cation based process will be a stepwise addition of B and H substituents, enabling a complementary addition geometry to be accessed. This will allow for the inexpensive synthesis of important organic building blocks that have hitherto been inaccessible or required complex multi-step syntheses.Throughout the commercial viability of this research will be ensured by the continual use of inexpensive reagents and by borylating alkenes and alkynes of relevance to the pharmaceutical and organoelectronic industries. The combination of borenium cation with alkenes and alkynes will provide access to a range of important compounds currently either inaccessible or not commercially viable using established methodologies.