Due to its unique three-dimensional scaffold with spatially well-defined substituents, the cyclopropane moiety is widely prevalent in biologically active compounds and therefore, the development of methods for their introduction into complex molecules is appealing. Since functionalized cyclopropanes represent attractive building blocks, we were interested in gem-borosilylcyclopropanes, as the boronic acid and silyl groups are useful synthetic handles for further transformations. The blueprints of light-harvesting natural biomolecules inspired chemists to harness photons into chemical energy using transition metal complexes or organic dyes. Previously, our group has reported a metal-free borocyclopropanation of styrenes using UVA light and continuous flow technology. In addition, while the silyl group can be a very polyvalent functionality, the C-Si bond can be used as a bioisotere of the C-C double bond. Although C-C double bonds are prevalent in bioactive compounds, pharmacodynamic properties were revealed improved when a silylated functionality was introduced instead. In this work, organocatalyzed visible light-mediated and user-friendly conditions were optimized and applied to diverse styrenes leading to a wide range of highly valuable silylcyclopropylboronate esters. To illustrate the potential of the reaction in late-stage functionalization, styrene derivatives of natural or drug-like molecules were synthesized. Orthogonal functionalization of borosilylcyclopropane allowed to add complexity to drug-like molecules.

Organocatalyzed visible-light mediated synthesis of gem-borosilylcyclopropanes

ACS Spring 2022

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