New Routes to Rare Aromatic BN-Heterocycles: 1,3-Azaborinine and 1,3-Azaborolyl-Anion Derivatives

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The dihydro-azaborinines are an important class of polar aromatic surrogates of benzene. While the 1,2- and 1,4-isomers have long been known and have found many applications, the first 1,3-azaboronine examples were only reported in 2011. In 2019 we successfully developed an alternative synthesis to the rare 1,3-dihydro-1,3-azaborinines, proceeding by means of a multi-component cyclization reaction by coupling alkyne and isonitrile components at a fluoroarylborane. In this project we will significantly develop this convenient synthetic process, including making variations of the substitution pattern at carbon, nitrogen and boron. Synthetic routes to quinoline- and indol-like 1,3-azaborinine annulations will be tried. The stepwise multi-component synthesis can easily be stopped at the stage of the five-membered dihydro-1,3-azaborole intermediates. We could show in our preliminary work to this project that this opens a convenient route to the previously unknown dihydro-1,3-azaborolyl anions, which are heterocyclic analogues of the ubiquitous Cp-ligands. We want to use this entry for the development of the chemistry of the respective dihydro-1,3-azaborolyl complexes of a variety of metals and explore their application in catalysis. This will include the exploration of some chiral derivatives and their potential use in stereoselective olefin polymerization as well as in asymmetric catalysis.