Boron-mediated sequential alkyne insertion and C-C coupling reactions affording extended π-conjugated molecules.

Yoshiaki Shoji,Naoki Shigeno,Kumiko Takenouchi,Haruka Sugiyama,Naoki Tanaka,Sho Muranaka,Fatin Hajjaj,Takanori Fukushima

doi:10.1038/ncomms12704

Yoshiaki Shoji, Naoki Shigeno + Show 6 more

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https://doi.org/10.1038/ncomms12704

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Abstract

C–C bond coupling reactions illustrate the wealth of organic transformations, which are usually mediated by organotransition metal complexes. Here, we show that a borafluorene with a B–Cl moiety can mediate sequential alkyne insertion (1,2-carboboration) and deborylation/Csp2–Csp2 coupling reactions, leading to aromatic molecules. The first step, which affords a borepin derivative, proceeds very efficiently between the borafluorene and various alkynes by simply mixing these two components. The second step is triggered by a one-electron oxidation of the borepin derivative, which results in the formation of a phenanthrene framework. When an excess amount of oxidant is used in the second step, the phenanthrene derivatives can be further transformed in situ to afford dibenzo[g,p]chrysene derivatives. The results presented herein will substantially expand the understanding of main group chemistry and provide a powerful synthetic tool for the construction of a wide variety of extended π-conjugated systems.

Highlights

C–C bond coupling reactions illustrate the wealth of organic transformations, which are usually mediated by organotransition metal complexes
Several studies have demonstrated that main group compounds can exhibit remarkable reactivity, which is typical of transition metals[1]
In the context of organic transformations, many organotransition metal compounds allow the insertion of unsaturated compounds into their metal–carbon bonds, and some of the resulting complexes subsequently undergo elimination of the metal moiety to mediate crosscoupling reactions[7,8] (Fig. 1b)

Summary

Introduction

C–C bond coupling reactions illustrate the wealth of organic transformations, which are usually mediated by organotransition metal complexes. In the context of organic transformations, many organotransition metal compounds allow the insertion of unsaturated compounds into their metal–carbon bonds, and some of the resulting complexes subsequently undergo elimination of the metal moiety to mediate crosscoupling reactions[7,8] (Fig. 1b). This sequence of reactions still sets the chemistry of transition metals apart from that of main group elements. This absolutely unexpected observation prompted us to further explore the reactivity of these chloro-substituted borepins

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Conclusion