Synthesis of BN hexahydronaphthalene via triallylborane and dialylamine

Abstract

Polycyclic aromatic hydrocarbons (PAHs) have always been of great importance in the context of chemical and materials science research,[1] with a recent emphasis placed on the modulable photophysical properties of extended π-systems in certain sectors of organic conductors,[2] among others. The cause of its properties relies in the number of π-conjugations and the electronic delocalization. However, new applications appear when applying the BN isosterism. That means including a boron-nitrogen bond to substitute a carbon-carbon bond. In doing so, the “normal” apolar C=C unit in such molecules is replaced with the more polar BN units, thus creating a dipoles and causing differences in reactivity and properties.[3][4][5] This has led to the potential of aromatic BN compounds for the isosteric substitution of phenyl and naphthyl groups in medicinal chemistry, thus creating new avenues in drug design through BN-isosterism.[6] The aromatic relocation of electrons provides stability to the molecule and allows its study. Still limited by the lack of synthetic methodologies for the preparation of these compounds in sufficient quantities, aromatic BN compounds are of great interest. On the other hand, the effects of these substitutions are still poorly studied, and any progress is extremely important. The aim of this project has been to improve the synthesis of a particular member of the BN aromatic family, specifically of one of the isomers of the so-called BN-naphthalene core. While this compound has gained much attention as building block in organic electronic design, its synthesis has remained highly challenging and low yielding. In this TFG project, we aim to provide a much-improved route towards these molecules. Specifically, with the reaction between triallylborane and dialylamine for the formation of the adduct, and subsequent release of propene to form a key tetra-allylic precursor. This species then undergoes efficient ring-closing olefin metathesis (RCOM) by treatment with Grubbs type I catalyst. The metathesis of enynes with these reagents has also been studied, following the same procedure but using di-propargylamine in the propenolysis step