The β Effect of Silicon and Related Manifestations of σ Conjugation

Lambert, Joseph B.; Zhao, Yan; Emblidge, Robert W.; Salvador, Lourdes A.; Liu, Xiaoyang; Jeung-Ho, So; Chelius, Erik C.

doi:10.1021/ar970296m

Cited by 262 publications

(188 citation statements)

References 42 publications

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“…Interestingly, the sp 3 hybrid structure of the central carbon of the t-Bu group in 1 changed while the structure of the TMS group in 2 preserved its sp 3 hybrid structure. The aforementioned TMS stabilization effect of the α-silicenium ion is interesting because in analogous carbocation structures, silyl group stabilization at the β-position is well-known, 4 but there is a reported destabilization effect at the α-position. 5 The α-silicenium ion stabilization likely arises from the higher polarizability of silicon and the hyperconjugation by Si-C bonds in the TMS group.…”

Section: Resultsmentioning

confidence: 99%

The unique reactivity of "super silyl" in organic synthesis: A theoretical study

Akakura¹,

Boxer²,

Yamamoto³

2007

Arkivoc

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We recently developed a new use of the super silyl group in organic reactions, and showed that it has unique reactivity. One of the reactions using this reagent is diastereoselective Mukaiyama aldehyde cross-aldol reaction catalyzed by a highly active Brønsted acid. This reaction produced syn-1,3-diol derivatives with high yield and high stereoselectivity. Certain features and outcomes of the reaction were not clear, so we decided to investigate the reaction mechanism through a theoretical study. In this paper, structures of super silyl species were observed as the subject of study. First 1 and 2 were investigated so that the effect of a TMS group adjacent to a silicenium ion could be determined. Interestingly, it was found that the TMS group stabilized the silicenium ion. It is presumed that the stability of the tris(trimethylsilyl) silicenium ion (TTMSS+) is related to the unique reactivity of super silyl group in theses reactions. We also investigated equivalent structures of silyl enol ethers (SEE) and found an unusual structure of 5. This structure is a result of unusual interactions between the silyl portion and enol ether (EE) portion; 1) C=C and Si-Si bonds, 2) lone pair of oxygen and Si-Si bond.

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Section: Resultsmentioning

confidence: 99%

The unique reactivity of "super silyl" in organic synthesis: A theoretical study

Akakura¹,

Boxer²,

Yamamoto³

2007

Arkivoc

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“…The remarkable potential of 119 Sn NMR in the analysis of mixtures and structural assignment is due to the sensitivity of tin chemical shifts towards small structural changes four or even five bonds away from the tin in comparison with trialkylboranes (δ 11 B 87 ± 1 ppm 31 ) can be traced to hyperconjugative interactions (σ conjugation) 32 between boron and neighbouring C-C and M-C (M Si, Sn) bonds. These interactions require a preferred conformation of the C 2 B plane of the 9-BBN or the Et 2 B group, which depends on steric repulsion exerted by other substituents, in particular on C-3 and C-4.…”

Section: Reactions Of the Alkenes 2 And 3 With Me 3 Sn-c C-snme 3 (4)mentioning

confidence: 99%

1,1‐Organoboration of bis(trimethylstannyl)ethyne with trimethylsilyl‐ and dimethylsilyl‐dialkylboryl‐substituted alkenes: organometallic‐substituted allenes

Wrackmeyer

Tok

Bhatti

et al. 2003

Applied Organom Chemis

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The reactions of bis(trimethylstannyl)ethyne, Me 3 Sn-C C-SnMe 3 (4), with trimethylsilyl-or dimethylsilyl-dialkylboryl-substituted alkenes 1-3 afford organometallic-substituted allenes 5, 6 and 8, 9 in high yield. In the case of (E)-2-trimethylsilyl-3-diethylboryl-2-pentene (1), a butadiene derivative 7 could be detected as an intermediate prior to rearrangement into the allene. All reactions were monitored by 29 Si and 119 Sn NMR, and the products were characterized by an extensive NMR data set ( 1 H, 11 B, 13 C, 29 Si, 119 Sn NMR).

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“…[2] Although it is still a matter of debate whether the influence of silyl groups on reaction rates and stereochemistry should be ascribed to electronic or steric factors, the so-called electronic β effect of a silyl group on carbocations 1 and the γ effect of silicon on carbocations 2 are well studied. [3] The β-silyl stabilization effect of a carbocation 1 is attributed to an interaction of the vacant orbital of the carbocation with the C-Si σ bond. This β effect can lead to carbocation formation at rates up to 10 11 times faster than those of unsilylated analogues.…”

Section: Introductionmentioning

confidence: 99%

Removable Silyl Group as a “Masked Proton” in Oxy‐2‐oxonia(azonia)‐Cope Rearrangement: Applications in Stereoselective Total Synthesis of Natural Macrolides

Zou

Zhou

et al. 2015

Eur J Org Chem

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In the presence of a Lewis acid, trimethylsilyl‐substituted β,γ‐unsaturated ketones and aldehydes (imines) undergo nucleophilic addition to produce zwitterionic intermediates, followed by oxy‐2‐oxonia(azonia)‐Cope rearrangements to give homoallylic esters (amides). In the case of TMS‐containing 2‐vinylcycloalkanones, the process results in ring‐enlargement, providing 10‐ to 16‐membered lactones. This protocol was applied to the total synthesis of (R)‐phoracantholide I.

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The β Effect of Silicon and Related Manifestations of σ Conjugation

Cited by 262 publications

References 42 publications

The unique reactivity of "super silyl" in organic synthesis: A theoretical study

The unique reactivity of "super silyl" in organic synthesis: A theoretical study

1,1‐Organoboration of bis(trimethylstannyl)ethyne with trimethylsilyl‐ and dimethylsilyl‐dialkylboryl‐substituted alkenes: organometallic‐substituted allenes

Removable Silyl Group as a “Masked Proton” in Oxy‐2‐oxonia(azonia)‐Cope Rearrangement: Applications in Stereoselective Total Synthesis of Natural Macrolides

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