Benzyl ethers electronic effects

We have briefly looked at the electronic effects on this mechanism by the competition experiment of two primary alcohols (2-phenethyl ethanol and benzyl alcohol). The information we obtained only explained the importance of the nucleophilicity of the alcohol. In order to determine the electronic effects on the dissociating alcohol, an experiment could be performed that treats the silyl ether of a primary alcohol with a second primary alcohol, both alcohols having different electronic environments (Scheme 40). The ratio of exchange product (B) to expected product (A) would be an indication of the effect of the electronic environment on the dissociating alcohol in intermediate IV of Figure 11. 

For styrene-based random copolymers, functional groups can be introduced into the polymer chains via copolymerization with functional styrene derivatives, because the electronic effects of the substituents are small in the metal-catalyzed polymerizations in comparison to the ionic counterparts. Random copolymer R-6 is of this category, synthesized from styrene and />acetoxystyrene.372 It can be transformed into styrene// -vinylphenol copolymers by hydrolysis.380 The benzyl acetate and the benzyl ether groups randomly distributed in R-7 and R-8 were transformed into benzyl bromide, which can initiate the controlled radical polymerizations of styrene in the presence of copper catalysts to give graft copolymers.209 Epoxy groups can be introduced, as in R-9, by the copper-catalyzed copolymerizations without loss of epoxy functions, while the nitroxide-mediated systems suffer from side reactions due to the high-temperature reaction.317... 

The acrylate- and methacrylate-derivatized r 5-(benzene)tricarbonylchromium monomers 20 65,66,68,72 21,69>72 and 2273 (Scheme 1.2) were synthesized from benzyl alcohol or 2-phenylethanol when reacted with Cr(CO)6. The alcohols were esterified with either acrylyl or methacrylyl chloride in ether/pyridine and purified by multiple recrystallizations from CS2. Homopolymerizations proceeded in classic fashion with no special electronic effects from the rr-complexed Cr(CO)3 moiety.65,73 Acrylate 20 was copolymerized with styrene and methyl methacrylate and the reactivity ratios were obtained.65 Acrylate 21 and methacrylate, 22, copolymerized readily with styrene, methyl acrylate, acrylonitrile, and 2-phenylethyl acrylate to give bimodal molecular-weight distributions using AIBN initiation.69 Copolymerization of 20 with ferrocenylmethyl acrylate, 2, generates copolymers with varying mole ratios of two transition metals, Cr and Fe (see structure 34).65... 

Metal Free Transition metal catalysts are highly effective for C—H bond activation. However, transition metal complexes are not only expensive, but also difficult to remove from the reaction products, resulting in toxicity concerns. DDQ is a well-known oxidant in organic chemistry [33]. For many years, it has been used for the oxidation of alcohols to ketones and aromatization. The first intermolecular C—C bond formation was realized by DDQ-mediated Mukaiyama-type aldol reactions [34], The reactions of electron-rich benzyl ethers and silyl enol ethers afforded 3-alkoxy-3-phenylpropionyl derivatives at ambient temperature with moderate to excellent yields (Equation 11.12). 

The ease of interaction of Ni(0) complexes with organic substrates has been shown to depend upon both the ligands on nickel and the solvent. The presence of a,a-bipyridyl with the Ni(0) complex and the alkyne led to the isolation of a nickelacyclopropene, an observation in accord with the recently proposed metallocyclic pathway for the Ni(0)-cata-lyzed trimerization of alkynes. Allylic and benzylic ethers and epoxides have been observed to undergo oxidative insertion of Ni(0) into their C-0 bonds with solvent (TMEDA > THE > Et O > CeHe) and ligand (EtsP > PhsP a,a-bipy > COD) effects consistent with an electron-transfer attack by Ni(0). With such sulfur heterocycles as dibenzothiophene, phenoxathiin, phenothiazine, and thian-threne, a 1 1 admixture of (COD)2Ni with a,a-bipyridyl gave as the principal product the desulfurized, ring-contracted cyclic product. 

Oxetanones (/3-Lactones).—Electronic effects in the thermal decarboxylation of 3- and 4-aryl-2-oxetanones indicate that the reaction is concerted but proceeds through a polar transition state. Thermal decarboxylation of /3-lactones is the key step in a convenient synthesis of benzyl enol ethers from a-benzyloxyacetic acids (Scheme 9) and also in the formation of (E)-l-halogeno-l-cyano-2-aryl-ethenes from halogeno-cyanoketens and aryl aldehydes. 

Both steric and electronic effects favored the observed ring opening in 28 producing the /S-methyl aldehyde (Scheme Addition of Et3N helped in suppressing the hydrogenolysis of the benzyl ether functional group. 

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