Chemoselective Palladium‐Catalyzed Suzuki‐Miyaura Cross‐Coupling of (Diborylmethyl)silanes with Alkenyl Bromides

Abstract

Herein, we report the development of a palladium‐catalyzed chemoselective cross‐coupling of (diborylmethyl)silanes with alkenyl bromides. The reaction shows broad scope with respect to alkenyl bromides and (diborylmethyl)silanes, affording a range of α‐silyl‐substituted allylic boronate esters in good‐to‐excellent yields. The practicality of the developed coupling reaction is demonstrated by the gram‐scale synthesis of α‐silyl‐substituted allylic boronate ester.

α‐Boryl Carbanions: The Influence of Geminal Heteroatoms in C−C Bond Formation

“…[22] The same authors have reported a method for synthesizing various α-silyl-substituted allylic boronate esters through the palladium-catalyzed chemoselective coupling of (diborylmethyl)silanes with alkenyl bromides under mild conditions. [23] Borylsilyl-methanes can also be substituted with heteroatoms as Ge, Sn. [24] Shimizu et al, prepared [CH-(SnBu 3 )(Bpin)(SiMe 2 Ph)] (3) and generated the corresponding carbanion with LDA followed by germylation with Me 3 GeCl (Scheme 9a).…”

“…This methodology established the Pd(TFA) 2 as catalyst precursor of choice and NaOMe as base, requiring NaI as additive for quantitative conversion, although its role in the mechanism remains unclear (Scheme 8b) [22] . The same authors have reported a method for synthesizing various α‐silyl‐substituted allylic boronate esters through the palladium‐catalyzed chemoselective coupling of (diborylmethyl)silanes with alkenyl bromides under mild conditions [23] …”

α-Boryl Organometallic Reagents in Catalytic Asymmetric Synthesis

“…An early example of the catalytic synthesis of achiral α-boryl silanes was developed by Suginome, who used iridium-catalyzed C–H borylation of tetraalkylsilanes or ruthenium-catalyzed C–H silylation of methylboronic acid derivatives. A Pd-catalyzed cross-coupling of (diborylmethyl)­silanes was also developed recently to prepare racemic α-boryl silanes …”

“…A Pd-catalyzed cross-coupling of (diborylmethyl)silanes was also developed recently to prepare racemic α-boryl silanes. 80 The first catalytic approach to nonracemic α-boryl silanes was accomplished by the Yun group in 2012. 81 Through copper-catalyzed chemoselective double borylation of silylacetylenes 149, α,β-diborylalkyl silanes 150 were prepared with syn selectivity.…”

Photoredox of Gem-Diborylalkenes: A Novel Reactivity Toward Diverse 1,1-Bisborylalkanes

“…Significantly, the reaction shows very high regioselectivity when conjugated diene gem-diboryl (7aj) was subjected to the photoredox reaction conditions; the 1,2-addition product (6aj) was observed as the sole product in 41% yield (Scheme 3A). Interestingly, the decarboxylative addition reaction of proline reacts in a regioselective manor when reacted with E-1,2bisboraneyl-1-silane [24] (7ak), yielding a rapid access to the γamino 1,2-bisboryl-1-silane product (6ak), which passes through a boron-silicon-stabilized radical intermediate [25] (III-ak) (Scheme 3B). This radical has an SRE of xx Kcal/mol.…”