Three or Four Heteroatoms Including at Least One Boron

Research involving the preparation and utilization of five-membered boron containing heterocycles has continued to grow exponentially over the last 10 years. Use of these compounds in academia and industry will continue to flourish because of the low toxicity of many boron containing compounds. Furthermore, a variety of functional groups such as alcohols, amines, aldehydes, ketones, carboxylic acids, etc. can readily be obtained by further transformations of organoboranes. The application of organoboranes in synthesis can be attributed to the early work of Nobel Laureate Herbert C. Brown and more recently the Nobel Laureate Akira Suzuki. As in the previous issue CHEC-III,1 this chapter covers as much of the relevant literature as possible allowing for space requirements. Hydroboration methods involving five-membered boron heterocycles continues to be a reliable procedure for the synthesis of organoboranes moreover, recent developments in catalytic asymmetric and chemoselective borylation add further grounds for using this approach in the synthetic laboratory. Several publications involving asymmetric borylation methods are discussed within this update, many focusing on preparing previously challenging alkyl boronic esters. Elaborate and newly modified Miyaura-borylation methods are also discussed. Excitingly, the formation of complex boronic esters are playing a role in larger macrocycle formation and intricate self-assembly processes. A series of heterocyclic ring systems containing boron and a range of other heteroatoms are also found within this chapter. This alone is a prevalent and popular field with very interesting and novel ring systems being recently discovered. It is expected in the coming years the growth in photochemical borylative processes along with non-transition metal cross-coupling approaches will continue to grow. These early ground breaking processes are covered here.