167282-62-4Relevant academic research and scientific papers
The γ-silicon effect. IV. The solvolysis mechanism of 3-(aryldimethylsilyl)propyl p-toluenesulfonates
Fujiyama,Nakashima,Kim,Fujio,Tsuno
, p. 429 - 438 (2007/10/03)
The solvolysis of 3-(aryldimethylsilyl)propyl p-toluenesulfonates was described based on the effects of substituents, solvents, and deuterium isotope, in comparison with the γ-silyl-assisted solvolysis of 3-(aryldimethylsilyl)-2,2-dimethylpropyl toluenesulfonates. The solvent effect on the simple γ-silyl assisted system showed the nucleophilic assistance of solvent, but failed to correlate linearly with the extended Winstein-Grunwald equation, substantiating that the reaction should not proceed through either the formation of the cation intermediate of the SN2 mechanism. This suggested that the reaction occurs in competition between γ-silyl-assisted (kSi) and solvent-assisted (ks) pathways, and that the competition ratio varies with solvents and with aryl substituents. Product analysis revealed that the former pathway gave only cyclopropane and the latter gave only the substitution products. Using product ratios, the overall rate constant (kt) value could be dissected into the partial rate constants kSi and ks for the two pathways. The effects of aryl substitutes at the γ-silyl atom on kSi pathway were correlated with unexalted σ°(normal substituent constant) parameter, giving the ρ values of -1.0 in 60E and -1.32 in 97Tw, and reflecting the delocalization of incipient carbocationic charge by participation of the Si-Cγ bond. The substituent effects on the ks pathway were negligible, which is in line with the remote reaction center in the concerted SN2 mechanism.
The Phenyldimethylsilyl Group as a Masked Hydroxy Group
Fleming, Ian,Henning, Rolf,Parker, David C.,Plaut, Howard E.,Sanderson, Philip E. J.
, p. 317 - 338 (2007/10/02)
A phenyldimethylsilyl group attached to carbon can be converted into hydroxy group 1->5, with retention of configuration at the migrating carbon, by any of three main methods.The first involves protodesilylation, to remove the phenyl ring from the silicon atom, followed by oxidation of the resulting functionalized silicon atom using peracid or hydrogen peroxide.The second uses mercuric acetate for the same purpose, and can be combined in one pot with the oxidative step using peracetic acid.This method has a variant in which the mercuric ion is combined with palladium(II) acetate, both in less than stoichiometric amounts.The third uses bromine, which can also be used in one pot in conjuction with peracetic acid.In this method, but not in the method based on mercuric acetate, the peracetic acid may be buffered with sodium acetate.The method using bromine as the electrophile for removing the benzene ring has a more agreeable variant in which it is administered in the form of potassium bromide, which is oxidised to bromine by the peracetic acid.The scope and limitations of each of these methods are reported with a range of examples possessing between them many of the common functional groups.Simple benzene rings, alcohols, ethers, esters, amides and nitriles are compatible with all three methods, and ketones do not undergo Baeyer-Villiger reaction under any of the conditions.Amines, however, are oxidised to amine oxides.Ketones may be brominated in the third of the three main species.The absence of acid in the third method makes it especially valuable when the phenyldimethylsilyl group has a neighbouring nucleofugal group such as hydroxy or acetoxy.Carbon-carbon double bonds are incompatible with the methods, except for terminal monosubstituted double bonds, which can survive the conditions used in the first of the three methods.
