Stereospecific Synthesis of Silicon-Stereogenic Optically Active Silylboranes and their Application to Synthesis of Chiral Organosilanes

Silylboranes have widespread applications in organic synthesis as versatile silylation reagents, which has inspired interest in studying methods for their synthesis. Silicon-stereogenic optically active silylboranes would allow the introduction of silicon-stereogenic silyl groups into various molecules. However, the synthesis of such silicon-stereogenic silylboranes remains unknown to date. Here, we report the first synthesis of silicon-stereogenic optically active silylboranes via stereospecific Pt(PPh3)4-catalyzed Si–H borylation of silicon-stereogenic hydrosilanes in high yield and perfect enantiospecificity (100% es) with retention of the configuration. Furthermore, the first characterization of silicon-stereogenic silyl-boranes by single crystal X-ray diffraction analysis was reported. This protocol is suitable for the stereospecific synthesis of silicon-stereogenic trialkyl-, dialkylbenzyl-, dialkylaryl-, and diarylalkyl-substituted silylboranes with excellent enantiomeric purity. The utility of the silicon-stereogenic silylboranes is demonstrated in silicon–silicon cross-coupling, transition-metal-catalyzed carbon–silicon bond-forming cross-coupling, and conjugate addition reactions with perfect enantiospecificity (100% es). The absolute configurations of the chiral silicon products were successfully confirmed by single-crystal X-ray diffraction analysis. The established synthetic strategy can be expected to expand the chemical space of silicon-stereogenic optically active organosilicon compounds with potentially interesting properties.