Ethers reactions with carbonyl

For primary alkyl phenyl ethers 47, their hthiation under catalytic conditions (DTBB, 5%) in THF at room temperature gave the expected alkyUithiums, which by reaction with carbonyl compounds afforded, after hydrolysis, the expected alcohols 48 (Scheme 15) . In this case, only the O—Caiiyi bond cleavage was observed . On the other hand, the reaction shown in Scheme 15 failed for secondary (R = i-Pr) or tertiary (R = f-Bu) starting materials. 

Tetrahydrofuran itself can be opened using either the stoichiometric or the catalytic version of arene-promoted lithiation, but both cases need the activation by boron trifluoride. The catalytic reaction was performed by treating the solvent THF 324 with the complex boron trifluoride-etherate and a catalytic amount (4%) of naphthalene. The intermediate 325 was formed. Further reaction with carbonyl compounds and flnal hydrolysis yielded the expected 1,5-diols 326 (Scheme 95), which could be easily cyclized to the corresponding substituted tetrahydropyrans under acidic conditions (concentrated FlCl). 

Using chiral catalysts, not only various enantioselective Mukaiyama and vinylogous Mukaiyama aldol reactions have been developed but also asymmetric reactions of a,a-difluoro silyl enol ethers (1) with carbonyl compounds have been reported ... 

Resin-bound amines can be converted into imines [710,711] or enamines by reaction with carbonyl compounds (Entries 6 and 7, Table 3.39). Resin-bound enamines have also been prepared by Michael addition of resin-bound secondary amines to acceptor-substituted alkynes [712], by Hg(II)-catalyzed addition of resin-bound secondary amines to unactivated alkynes [713], by addition of C-nucleophiles to resin-bound imino ethers [714], and by chemical modification of other resin-bound enamines [712,713,715], Acceptor-substituted enamines ( push-pull alkenes) are not always susceptible to hydrolytic cleavage by TFA alone and might require aqueous acids to undergo hydrolysis [716]. 

Silyl enol ethers undergo reaction with carbonyl compounds promoted by Lewis acids, but especially titanium tetrachloride. The reaction is thought to proceed via a titanium chelate which inhibits the reverse aldol process and the regiochemical integrity of the starting silyl enol ether is retained (Scheme 102).373... 

The stereochemistry of the ene reaction with carbonyl compounds has been investigated by Ishikawa and coworkers with me.vo-(550) and rac-Ph(Et)MeSi—SiMe(Et)Ph as silene precursors251. With acetone and acetaldehyde the reactions were found to be highly diastereoselective when run in ether or toluene. In electron-donating solvents like THF or acetonitrile the diastereoselectivity decreased, and this was ascibed to a stepwise reaction. 

The formation of a 1 1 complex between open form of 16b,c and Ba2+, Pb2+ leads to a large bathochromic effect and the decrease in the rate constant for dark ring-closure reaction. The effect is explained by the formation of the anion- capped complex of metal cation located in crown ether cavity with carbonyl oxygen atom (Scheme 20). Substantial difference in the changes of magnitude of /c,/s 1 was obtained for the complexes of mono- and bischromene 16b,c with Ba2+ (Table 3). The difference is due to in the complex of 16c with Ba2+ the carbonyl atoms of both chromene units participate in the formation of anion- capped complex, whereas, the anion- capped ... 

Silyl enol ethers, Reaction of carbonyl compounds with in situ generated BrSi(CH3)3 and triethylamine results mainly in the thermodynamic silyl ether, usually the (Z)-isomer. 

Reactions of the Lithiated Bis-Iactim Ether 22 with Carbonyl Compounds and Benzoylchloride... 

The above transformation has two different goals 21,22) 1) To increase chemo-, regio-, diastereo- and enantioselectivity in the reaction with carbonyl compounds (Sections C-E), and 2) to make certain reaction types amenable which do proceed readily with classical reagents, e.g., methylation of tertiary alkyl halides, alcohols and ethers, and direct geminal dialkylation of ketones (Section F). It turns out that organotitanium compounds are usually complementary to Li, Mg, Zn, Fe, Ni, Cu and Pd reagents. So far, experience in the above two areas points to the following positive aspects ... 

Allylation andaldol reaction. Diallylstannane and silyl enol ethers condense with carbonyl compounds to furnish homoallylic alcohols and p-hydroxy ketones, respectively. A mixture of HjO, EtOH, and toluene is a suitable reaction medium as CufOTflj is stable in water. 

Cyclic ethers would be expected to undergo ring-opening reactions with carbonyl difluoride as with phosgene. Epoxyethane reacts with two moles of COFj, in the presence of pyridine, according to the following equations [24a] ... 

As discussed in Section 2.3.3.1, enol stannyl ethers react with carbonyl compounds readily without the need for catalysts. However, catalytic amounts of AgBp4 and h have bron found to improve considerably the yield of the condensation of the tin(II) enol ether (159) with the azetidinone (93). The use of a catalytic amount of PdCl2[P(o-MeC6H4)3]2 improves the yield of the reactions between enol stannyl(IV) ethers and aldehydes. ... 

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