16205-87-1Relevant academic research and scientific papers
γ-silyl-substituted norbornyl carbocations and carbenes
Creary, Xavier,Heffron, Anna
, p. 2547 - 2555 (2014)
endo-2-Trimethylsilyl-anti-7-norbornyl triflate undergoes solvolysis reactions 1.8 × 104 faster than 7-norbornyl triflate in CD 3CO2D and 1.3 × 105 times faster in CF3CH2OH. The exclusive substitution products with retained stereochemistry point to a significantly stabilized γ-trimethylsilyl carbocation intermediate. The endo-2-trimethylsilyl-7- norbornyl carbene gives a major rearrangement product where the trimethylsilyl-activated hydrogen migrates to the carbenic center. This rearrangement product implies stabilization of the carbene by the γ-trimethylsilyl group. Isodesmic computational studies (M062X/6-311+G* *) indicate that the endo-2-trimethylsilyl-7- norbornyl cation is stabilized by 16.2 kcal/mol and that the endo-2-trimethylsilyl-7-norbornyl carbene is stabilized by a smaller factor of 1.8 kcal/mol. By way of contrast, anti-7-trimethylsilyl-endo-2-norbornyl mesylate undergoes solvolysis in CD3CO2D only 2.6 times faster than endo-2-norbornyl mesylate and 9.4 times faster in CF 3CH2OH. The substitution products have only partially retained stereochemistry, and significant rearrangements are observed. The anti-7-trimethylsilyl-2-norbornyl carbene gives a rearrangement product via 1,3-hydrogen migration of the C6 hydrogen, which is completely analogous to the behavior of the unsubstituted 2-norbornyl carbene. Isodesmic calculations show that the anti-7-trimethylsilyl-2-norbornyl cation is stabilized by only 3.2 kcal/mol relative to the 2-norbornyl cation, and the corresponding anti-7-trimethylsilyl-2-norbornyl carbene is stabilized by a negligible 0.9 kcal/mol.
The β effect of silicon in the synperiplanar geometry
Lambert, Joseph B.,Chelius, Erik C.
, p. 8120 - 8126 (2007/10/02)
The effect of silicon on the development of β positive charge has been measured for the synperiplanar geometry of the Si-C-C-X fragment in endo-3-(trimethylsilyl)-endo-2-norbornyl esters (3). Solvent effects were used to demonstrate that solvolysis took place by a carbocation mechanism. When the leaving group X was mesylate (3-OMs) and the solvent was 97% trifluoroethanol, the β effect was found to be about 105 by comparison of the solvolysis rate with the analogous structure lacking the trimethylsilyl group, endo-2-norbornyl mesylate (5-OMs). Thus, the synperiplanar β effect is much smaller than the antiperiplanar β effect (about 1012 under similar conditions). The effect may be smaller because of poorer vertical overlap in the synperiplanar geometry or because the syn leaving group prevents optimal vertical overlap. Alternatively, the antiperiplanar effect may be larger because of contributions from nonvertical participation.
Cyclic Olefins by Anodic Oxidation of β-(Trimethylsilyl)carboxylic Acids. - β-(Trimethylsilyl)acrylic Acid Derivatives as Acetylene Equivalents in Diels-Alder Reactions
Hermeling, Dieter,Schaefer, Hans J.
, p. 1151 - 1158 (2007/10/02)
Trimethylsilyl-substituted dienophiles 1, 2, and 4 react with dienes 6-14 in 66-100percent yields to give β-trimethylsilyl-substituted carboxylic acids 15-25, some of which are hydrogenated to 26-31.These are decarboxylated-desilylated to cyclic olefins 35-47 by Non-Kolbe electrolysis in 45-91percent yields.The dienophiles 1, 2, and 4 are thus suitable acetylene equivalents for Diels-Alder reactions.
