10/01/2018 · Synthesis and chemistry of acyl silanes
Synthesis of Acyl Silanes
Acyl silane synthesis essay - granitewonderland
α-silyl carbanions are important synthons in organic synthesis. We present a "one flask" synthesis of unique non-solvated α-silyl organolithium compounds of type 2 (Scheme).Acyl silane 1 reacts with 2 molecules of tBuMe2SiLi (2b) to yield α-silyl carbanion 2 (X-ray).We suggest that this reaction occurs via a SET reduction of 1 by 2a to produce the dimeric triplet biradical intermediate 3a (EPR) which further reacts with 2b to yield 2. Thus, triplet biradical 3a, prepared independently in reaction of 1 with 2a and isolated as a stable salt (X-ray), reacts via a co-aggregated species 3b (EPR) with silyl radical 4 (generated in-situ from (tBuMe2Si)2Hg), eliminating tBuMe2SiOLi to yield 2.
The system described herein for acyl silane-ketone benzoin reactions offers a substantial improvement in the reaction scope of ketone-benzoin methodology. As Demir had illustrated the coupling of electron-deficient and non-enolizable ketones, we chose to address substrates with no general procedure for their synthesis in place. The coupling of aryl-methyl ketones was accomplished in a very general manner: electron-rich, neutral, and heteroaromatic substrates were tolerated, as well as those with ortho substituents (albeit in moderately lower yield). Dialkyl substrates were well tolerated, although α-branching exerts a strong negative impact on the yields via competitive quenching of the silylcyanohydrin. Sterically encumbered diaryl ketones underwent coupling in high yields once side reactions were minimized via a slow addition.
• Synthesized novel acyl silane moieties and developed methodology ..
Polarity umpolung has evolved into a powerful synthetic tool for making otherwise challenging carbon-carbon bonds. The archetypical example of this strategy is the benzoin reaction, the mechanism of which was elucidated by Lapworth in 1903 in his report on the homodimerization of aldehydes under cyanide anion catalysis. Since then, both N-heterocyclic carbene (NHC) and metallophosphite catalysts have been developed to promote the asymmetric benzoin and cross silyl benzoin (acyl silane-aldehyde benzoin) reaction, respectively. Despite the recent advances in the scope and utility of the benzoin reaction, the direct catalytic coupling of acyl anion equivalents to ketones has proved more challenging. Stoichiometric methods for ketone acylation do exist; however, general strategies are not in place for performing those reactions asymmetrically. Suzuki,, Enders,, and You have achieved NHC-catalyzed intramolecular aldehyde-ketone benzoin cyclization for the formation of five- and six-membered rings. Asymmetric variants for the intramolecular reaction have also been reported that proceed in up to 98% yield and 99% ee.
In a one-pot operation, two stereocenters and three new bonds were created with high selectivity. The reaction proceeds through a sequence of asymmetric alkynylation of an acyl silane, tandem Brook-type rearrangement, ene–allene cyclization, addition of an electrophile, and finally oxidation. It will be extremely useful in organic synthesis, and it is a new approach to synthetic transformations.
Klair and Stephen Rosenthal Abstract
Acylsilanes and Their Applications in Organic Chemistry
PATAI'S Chemistry of Functional Groups
Acyl iodides in organic synthesis: VII. Reactions with trialkyl(alkynyl)silanes,-germanes, and-stannanes
Acyl iodides in organic synthesis: VII ..
Synthesis of allylsilanes - Organic Chemistry Portal
Bulman Page, Sukhbinder S
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