Allylic alkoxides

When ethyl trifluoroacetylacetate is treated with an allylic alkoxide, tran-sesterification is followed by ester enolate Claisen rearrangement m a process that on decarboxylation yields stereospecifically the tnfluoromethyl ketone product [22] (equation 19)... 

As shown in Scheme 4-6, the reaction proceeds via a Ti(IV) mixed-ligand complex A bearing allyl alkoxide and TBHP anions as ligands. The alkyl peroxide is electrophilically activated by bidentate coordination to the Ti(IV) center. Oxygen transfer to the olefinic bond occurs to provide the complex B, in which Ti(IV) is coordinated by epoxy alkoxide and r-butoxide. In complex B,... 

If the alkenyllithium 43 is used as organolithium compound with 39, siloxyallyllithium reagents 44 are formed ". As example, the isomerization of the silyl(allyl)alkoxides 44 gives the corresponding lithio-(Z)-silyl enol ethers 45 which react with various electrophiles to give 46 (equation 17) . ... 

The [2,3] sigmatropic rearrangement pattern is also observed with anionic species. The most important case for synthetic purposes is the Wittig rearrangement, in which a strong base converts allylic ethers to a-allyl alkoxides.191... 

Excluding polymerizations with anionic coordination initiators, the polymer molecular weights are low for anionic polymerizations of propylene oxide (<6000) [Clinton and Matlock, 1986 Boileau, 1989 Gagnon, 1986 Ishii and Sakai, 1969 Sepulchre et al., 1979]. Polymerization is severely limited by chain transfer to monomer. This involves proton abstraction from the methyl group attached to the epoxide ring followed by rapid ring cleavage to form the allyl alkoxide anion VII, which isomerizes partially to the enolate anion VIII. Species VII and VIII reinitiate polymerization of propylene oxide as evidenced... 

It was further demonstrated, both by means of experimental (136) and ab initio (138) studies, that the use of an allylic alkoxide instead of an alcohol could be... 

The formation of methylperoxy intermediates—i.e., the product of a formal insertion of O2 into the metal-methyl bond—was substantiated by the observation of epoxidation of allylic alkoxides (Scheme 6), in analogy to the proposed mechanism for the Sharpless epoxidation utilizing tert-butylhydroperoxide (TBHP). A similar oxygen atom transfer from a coordinated alkylperoxide to olefin was also postulated for the epoxidation of olefins with TBHP catalyzed by Cp Mo(0)2Cl [31]. The use of organomolybdenum oxides in olefin epoxidafion cafalysis (albeit not with O2) has recently been reviewed [32]. 

If we consider the d0 metal-N,JV-dialkylhydroxylamino complexes (79), (80) and (81) as valid models for the reactive but unstable alkyl peroxide species Mo02(OOR)2, VO(OOR)3 or V203(00R)4, and Ti(OOR)4 presumably involved in catalytic oxidations, the low activity of vanadium and titanium for the epoxidation of simple alkenes could be interpreted by the fact that these alkenes cannot displace the O.O-bonded alkyl peroxide groups in the coordinatively saturated Vv- and Tiiv-alkyl peroxide species, whereas allylic alcohols can displace the alkyl peroxide groups by forming bidentate allylic alkoxides as in equation (75).162... 

The organozinc intermediate thus formed reacts with aldehydes as Grig-nard reagents do to form alcohols. In the presence of aluminum chloride, elimination of chlorine and fluorine from the vicinal carbons of the dichlorotrifluoroethyl group generates halogenated allylic alkoxides that are protonated to allylic alcohols, in the present case J, 2-chloro-3,3-difluoro-1 -phenylpropen-2-ol [114]. 

Ans. Epoxy allyl alkoxide and a solvent molecule coordinated to the Ti4+ ion. The former is then protonated and displaced by allyl alcohol. 

Variable temperature NMR studies of the parent titanium-tartrate system (3,4, 5) revealed that isopropoxide exchange, fluxional interconversion (in which the coordinated ester and uncoordinated ester carbonyls, as well as tartrate alkoxides, exchange with respect to the titanium) and epoxidation rate are closely coupled. Thus, the faster the isopropoxide exchange, the more a vacant site becomes available for coordination of allyl alkoxide and the faster the latter anion associates with the titanium. Likewise, faster fluxional interconversion indicates more rapid dissociation of the ester carbonyls in 3 and thence more rapid coordination of the alkyl hydroperoxide to give 4. 

The addition of an allyl alcohol to racemic allenyl sulfoxides results in vinyl ethers with the sulfinyl moiety at C-1 that undergo sigmatropic rearrangements upon distillation to produce 2,4-dienones after ehmination of sulfenic acid. In one example, an isomeric vinyl ether was obtained with a sulfinyl methyl substituent at C-2 that gave rise to a sulfinyl enone upon rearrangement [138]. In related work, the addition-elimination of an allyl alkoxide to a functionalized vinyl sulfoxide results in a sulfinyl enol ether that rearranges with loss of sulfenic acid to the unsaturated ester [139-141] (Scheme 21). 

In 1992 Kobayashi et al. [47] reported the first catalytic and enantioselective cyclo-propanation using the Furukawa modification [48] of the Simmons-Smith reaction of allylic alcohols in the presence of a chiral bis(sulfonamide)-Zn complex, prepared in-situ from the bis(sulfonamide) 63 and diethylzinc. When cinnamyl alcohol 62 was treated with EtgZn (2 equiv.), CHgIg (3 equiv.), and the bis(sulfonamide) 63 (12 mol %) in dichloromethane at -23 °C, the corresponding cyclopropane 64 was obtained in 82 % yield with 76 % ee (Sch. 26). They proposed a transition state XXIII (Fig. 5) in which the chiral zinc complex interacts with the oxygen atom of the allylic alkoxide and the iodine atom of iodomethylzinc moiety. They also reported the use of the bis(sulfonamide)-alkylaluminum complex 65 as the Lewis acidic component catalyzing the Simmons-Smith reaction [49]. 

Overman, L. E., Kakimoto, M. Preparation of rearranged allylic isocyanates from the reaction of allylic alkoxides with cyanogen chloride. J. Org. Chem. 1978,43,4564-4567. 

Although examples of catalytic conversion of allylic ethers are limited, Ty3-allyl alkoxide/aryloxide complexes have been isolated by the reaction of allylic ethers with zero-valent Ni and Pd complexes [10,14]. 

Allylic alkoxides react with phenylsulfanylcarbene (generated from the sulfide using potassium /ert-butoxide) to give the insertion products into C —H and C —metal bonds. The prenyl derivative is the only exception apart from the insertion products 2 and 3 (more probably, 3 is formed via alkylation of alkoxide with a-chloro sulfide), the carbene adds to the double bond to give 4. 

AOH = allylic alcohol OA = allylic alkoxide OE = epoxy alkoxide... 

The data reported above show that well characterized molecular adsorbed species of the three n-butene isomers are formed on the surface of MgFe204 n-butene oxy-dehydrogenation catalyst. Their vibrational perturbation indicates that a 7c-bonding occurs between the olefinic C=C double bond and Fe surface cationic centers. The results described above show that methyl-allyl alkoxides are also formed. Such species can also be produced by adsorption of but-3-en-2-ol (methyl-allyl alcohol) and can easily decompose to give butadiene gas. 

An evolution of alkoxides alternative to elimination, consists in a second oxidative dehydrogenation step to give the corresponding carbonyl compounds. This is what necessarly occurs with the C3 allyl alkoxide in the way producing acrolein from propene, because there are not hydrogens available for the elimination reaction [6]. We have observed spectroscopically this reaction at the surface of quite unselective catalysts like MgCr204 both from propene and butenes [17], and in the case of FeCrOj for butenes [15]. It is consequently evident that two competitive ways can occur, in our case ... 

Depending on the internal energy and the substituents attached to the pentacoordinate silicon adduct anions, not only exchange processes, like reaction 146, or substitutions (reactions 143-145) occur, but alkane elimination is also frequently observed, in particular under ICR conditions. Alkane elimination is favoured if the adduct does not contain a good leaving group (allyl, alkoxide). Three instructive examples are described in reactions 147-149164b. 

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