General Synthesis of Trialkyl- and Dialkylarylsilylboranes: Versatile Silicon Nucleophiles in Organic Synthesis

Abstract

Compared to carbon-based nucleophiles, the number of silicon-based nucleophiles that is currently available remains limited, which significantly hampers the structural diversity of synthetically accessible silicon-based molecules. Given the high synthetic utility and ease of handling of carbon-based boron nucleophiles, silicon-based boron nucleophiles, i.e., silylboranes, have received considerable interest in recent years as nucleophilic silylation reagents that are activated by transition-metal catalysts or bases. However, the range of practically accessible silylboranes remains limited. In particular, the preparation of sterically hindered and functionalized silylboranes remains a significant challenge. Here, we report the use of rhodium and platinum catalysts for the direct borylation of hydrosilanes with bis(pinacolato)diboron, which allows the synthesis of new trialkylsilylboranes that bear bulky alkyl groups and functional groups as well as new dialkylarylsilylboranes that are difficult to synthesize via conventional methods using alkali metals. We further demonstrate that these compounds can be used as silicon nucleophiles in organic transformations, which significantly expands the scope of synthetically accessible organosilicon compounds compared to previously reported methods. Thus, the present study can be expected to inspire the development of efficient methods for novel silicon-containing bioactive molecules and organic materials with desirable properties. We also report the first 11 B{ 1 H} and 29 Si{ 1 H} NMR spectroscopic evidence for the formation of i-Pr3SiLi generated by the reaction of i-Pr3Si-B(pin) with MeLi.

Synergistic Ni/Cu catalyzed migratory arylsilylation of terminal olefins

“…S1 online for details). Additionally, a trialkyl-substituted Si-B reagent [59] could also afford the migratory silylboration product under these conditions (4ao), but with lower efficiency. This finding reveals the electronic property of the silyl group can greatly affect the reactivity.…”

Design, Synthesis, and Implementation of Sodium Silylsilanolates as Silyl Transfer Reagent

“…In the case of p-bromoanisole, the yield of 40 under the current conditions (94%) is higher than the one in the known result with silylborane-based conditions. [18] While no coupling reaction with tert-butyldimethylsilyl (TBDMS) group and allyldimethylsilyl group has so far been reported under transition metal-catalyzed conditions with conventional silylating reagents, our silylation method with silylsilanolates Na + 3and Na + 4enabled an easy access to the TBDMS arene 41 (62%) and allylsilylated arene 42 (70%). These results indicate that the core structure of silylsilanolate would be generally more viable for the transmetalation of various silyl groups than the known silylating reagents.…”

“…With Na + 2 --Na + 4 -, introduction of other silyl groups was also possible in the current strategy (Table 4). Delivery of benzyldimethylsilyl group has been known to be inefficient with a disilane [6m] or silylborane [18] as a precursor. Under the optimized conditions with Na + 2 -, benzyldimethylsilyl group could be introduced to afford both electron-deficient and donating arenes 39 and 40 in high yields.…”

Design, Synthesis, and Implementation of Sodium Silylsilanolates as Silyl Transfer Reagent

“…Fluoro and vinyl substituents were also confirmed to be compatible (12,13). Substrates with electron-rich substituents, such as methoxy (p-, m-, o-OMe), silyloxy, amino, and amido-substituted aryls were generally transformed to arylsilanes (14)(15)(16)(17)(18)(19). A wide range of heteroaryl trimethylsilanes could also be synthesized under our silylation reaction.…”

“…In the case of p-bromoanisole, the current conditions gave pbenzyldimethylsilylanisole 40 in 90% yield, which is higher than the known result with silylborane-based conditions. 18 A sterically hindered tert-butyldimethylsilyl (TBDMS) group was introduced with Na + 3to give 41 in 62% yield. While no coupling reaction with allyldimethylsilyl group has so far been reported with conventional silylating reagents, our silylation method with silylsilanolate Na + 4enabled an easy access to the allylsilylated arene 42.…”