HMPA-Free Generation of Trialkylsilyllithium Reagents and Its Applications to the Synthesis of Silylboronic Esters

Abstract

Trialkylsilyllithium species have turned out to be facilely generated by treating hexaalkyldisilanes with methyllithium in the presence of tris(N,N-tetramethylene)phosphoric triamide (TPPA) as an activator, which can be trapped by boron electrophiles to afford silylboronic esters including long-awaited Me3Si–B(pin).

Photocatalytic Generations of Secondary and Tertiary Silyl Radicals from Silylboranes Using an Alkoxide Cocatalyst

“…For this purpose, silylboranes (Si–B) are one of the most convenient reagents as silyl anion equivalents produced upon activation with bases because they are storable and easy to handle . The recent advance in the borylation reaction of Si–H bonds has made silylboranes (including secondary ones) more readily available . Although many groups have developed base-mediated nucleophilic silylations using silylboranes, , there has been a single example of visible-light-induced one-electron oxidation of silylboranes reported by the Poisson group …”

General Concepts and Recent Advances in the Electrochemical Transformation of Chloro‐ and Hydrosilanes

“…In special cases polysilanes can be generated in the absence of a solvent, using only the dichlorosilane monomer with a complexing agent, such as HMPT, to solubilize the anodic generated metal chloride [91] . The less toxic tris( N , N ‐tetramethylene) phosphoric triamide (TPPA) might be a suitable stabilizing agent as well, as shown in the synthesis of organosilicon compounds [132] . The synthesis of functionalized polysilanes with more challenging side chains, such as hydroxy‐related, [56,123] or vinyl groups, [133] not accessible via the Wurtz route, can be achieved via the mild electrochemical reduction with molecular masses above 16 kDa.…”

“…[91] The less toxic tris(N,N-tetramethylene) phosphoric triamide (TPPA) might be a suitable stabilizing agent as well, as shown in the synthesis of organosilicon compounds. [132] The synthesis of functionalized polysilanes with more challenging side chains, such as hydroxy-related, [56,123] or vinyl groups, [133] not accessible via the Wurtz route, can be achieved via the mild electrochemical reduction with molecular masses above 16 kDa.…”

Preparations of Silyl Anions

“…To avoid the adverse effects caused by HMPA, Yoshida and Oestreich came up with a novel method of synthesis of silyllithium in the presence of less toxic tris(N, Ntetramethylene)phosphoric triamide (TPPA). The obtained silyllithium was further utilized in the synthesis of trialkylsilylboronic esters Et3SiB(pin) 28 (Scheme 8), 60 and the difficult Me3SiB(pin) 27 silylboronic ester due to its synthesis from low boiling parent silane Me3SiH (6.7 o C). Me3SiB(pin) was isolated on silica-gel column chromatography in an open atmosphere and its structure was confirmed by X-ray diffraction.…”

“…Me3SiB(pin) was isolated on silica-gel column chromatography in an open atmosphere and its structure was confirmed by X-ray diffraction. 60 Template for SYNTHESIS Thieme Scheme 8 Synthesis of silylboranes from trialkylsilyllithium…”