Allylic trifluoroacetates

When carried out under standard conditions with Et3SiH/TFA, reduction of acrolein leads to a mixture of allyl alcohol, 1-propanol, and di-n-propyl ether in addition to allyl trifluoroacetate and -propyl trifluoroacetate.434 The 1,2-reduction of cinnamaldehyde with triethoxysilane in the presence of fluoride ion provides the corresponding allyl alcohol in good yields (Eq. 261). 

The same ligand system was used in the allylic alkylation of allyl trifluoroacetate with sodium diethyl-2-methylmalonate showing a more or less constant conversion over 8 h (20 exchanged reactor volumes). This is in contrast to peripheral functionalized dendrimers (Section 4.4.2), which deactivated at longer reaction times. 

Thus, after the formation of the 7t-allyl complex 397 from the corresponding allyl trifluoroacetate, an exchange of ligand with triphenylphosphine generates 398. The formation of the phosphine-Pd complex 398 appears to be the key to successful cyclization, because the complex 397 failed to cyclize. 

The research group of Van Leeuwen reported the use of carbosilane de-ndrimers appended with peripherial diphenylphosphino end groups (i.e. 25, Scheme 26) [37]. After in situ complexation with allylpalladium chloride, the resultant metallodendrimer 25 was used as catalyst in the allylic alkylation of sodium diethyl malonate with allyl trifluoroacetate in a continuous flow reactor. Unlike in the batch reaction, in which a very high activity of the dendrimer catalyst and quantitative conversion of the substrate was observed, a rapid decrease in space time yield of the product was noted inside the membrane reactor. The authors concluded that this can most probably be ascribed to catalyst decomposition. The product flow (i.e. outside the membrane reactor)... 

Addition to linear 1,1-disubstituted allylic acetates is slower than addition to monosubstituted allylic esters. Additions to allylic trifluoroacetates or phosphates are faster than additions to allylic carbonates or acetates, and reactions of branched allylic esters are faster than additions to linear allylic esters. Aryl-, vinyl, alkynyl, and alkyl-substituted allylic esters readily undergo allylic substitution. Amines and stabilized enolates both react with these electrophiles in the presence of the catalyst generated from an iridium precursor and triphenylphosphite. 

De Groot et al. (18) prepared phosphine-functionalized carbosilane dendrimers of different generations (4, 8, 24, and 36 phosphine end groups) and used their palladium complexes as catalysts for the allylic alkylation of allyl trifluoroacetate with diethyl sodio-2-methylmalonate. 

The palladium catalyst supported on the dendrimer with 24 phosphine end groups (2) was used in a CFMR. In the continuous process a solution of allyl trifluoroacetate and sodium diethyl 2-methylmalonate in THF (including -decane as an internal standard) was pumped through the reactor. Figure 4 shows the conversion as a function of the amount of substrate solution (expressed in reactor volumes) pumped through the reactor. The reaction started immediately after the addition of the catalyst, and the maximum conversion was reached after two reactor volumes had passed, whereupon a drop in conversion was observed. It was inferred from the retention of the dendrimer (99.7% in dichloromethane) that the decrease was not caused by dendrimer depletion, and it was therefore ascribed to the... 

Fig. 4. Application of dendritic ligand 2 in the continuous allylic alkylation of allyl trifluoroacetate and sodium diethyl 2-methyhnalonate in a membrane reactor (Koch MPF-60 NF membrane, molecular weight cut-off = 400 Da) 18a).

Acylsilanes serve as acyl donors in the Pd-catalyzed cross-couplings with allyl trifluoroacetates,243 aryl halides,244 and alkenyl halides.2 Intramolecular acylation of alkynes with acylsilanes proceeds under catalysis by [RhCl(CO)2]2.246... 

Using 10mol% of [Rh(CO)2Cl]2 and 1 atm of CO, allyl trifluoroacetate 10 reacted rapidly at room temperature with the anion of malonate 9. Completion of the subsequent PKR required heating to reflux for 12-24 h [27] (Scheme 7). 

On the other hand, using cyclopropyl-substituted allylic trifluoroacetate 12 led to [5 + 2] cycloaddition product 13 after the temperature was raised to 80 °C (Scheme 8). Both procedures are experimentally simple since only a change in temperature is necessary to promote the second step of the sequential reactions. 

Allylic trifluoroacetates are very reactive with Pd reagents, generating -allyl palladium trifluoroacetates (equation 51), which can react further to produce cationic 7r-aUyl complexes when reacted with chelating amines (equation 52). The cationic complexes can also be synthesized from ly -dWyl palladium trifluoroacetates by treatment with HBF4 and ligands, L, producing PdL2( -allyl)+ BF4 complexes. 

The a-substituted 1-methyl allyl vinyl ether was shown to isomerize with a strong preference for the irons product (i.e., 95 % irons, 5 % cfe) . This corresponds to a conformational preference for equatorial methyl (as opposed to axial) in the chair transition state of about 2.4 kcal.mole . The identical value was calculated from the irons product preference in the allyl ester Claisen rearrangements (see a-methyl allyl acetate and a-trifluoromethyl allyl trifluoroacetate). 

Trifunctionalization of alkenes. Addition to a double bond using the combination of anhydrides leads to a thermally unstable selenoxide as the primary product. yyn-Elimination occurs and the allylic trifluoroacetate is susceptible to a second... 

Allyl ketones are prepared by cross-coupling of allyl esters with acyl metals. For the coupling, allyl trifluoroacetate (306) and the acylstannane 307 were used to provide the ketone 308 [112]. Similarly, acylsilanes such as 310 are used for the coupling with allyl trifluoroacetate 309 to give 311 [113]. For these couplings, use of allyl trifluoroacetate is important. No reaction occurred with allyl acetate. While ligandless palladium trifluoroacetate is most effective, Pd(OAc)2 shows low activity. 

Burgess and Ohlmeyer [30] have reported that electronic effects are important in catalyzed hydroboration, e.g., allylic acetates are hydroborated with less syn selectivity than allylic trifluoroacetate is [25], and proposed the general model [A] (Fig 5.4) for catalyzed hydroboration of chiral allylic alcohols. The model predicts that the OCOCF, substituent (good a acceptors) will preferentially orientate anti to the approaching rhodium complex. The largest of the other two substituents on the chiral center will occupy the outside position, and the smallest will reside in the inside (crowded) site and thus, syn selectivity will result... 

The proposed model [B] implies that syn selection in catalyzed hydroboration should decrease as the o-accepting character of the anti substituent decreases. This explains the higher syn selectivity in catalyzed hydroboration of allylic trifluoroacetates as compared with reactions of allylic acetates and carbamates [25]. The less diastereoselectivity of cationic complexes in hydroboration of chiral allylic systems than in the neutral catalyst systems [29, 30] is rationalized, as the latter have more electron density to shed via back-bonding. The anti selectivity in catalyzed hydroboration of the allylic acetate and trifluoroacetate is rationalized in terms of competition between the phenyl and acetate groups for the role of a acceptor. The further evidence is obtained in the case of pentafluo-... 

Another elegant example of a multicomponent aza-Sakurai reaction was reported by Jarvo in 2009 [99]. In this case, Pd(OAc)j was used as catalyst both for the generation in situ of the aUylsilane from allyl trifluoroacetate and HMDS and also for the allylation of the in situ formed imine fi om the corresponding aldehydes and anisidine (H NPMP) (Scheme 12.22). This was concluded after a study base on competition experiments. This procedure allows the synthesis of a variety of homoallylic amines in good to excellent yields (67-96%), starting from different substrates including electron-rich aromatic and aliphatic aldehydes. 

Allyl halides are probably the most common allylic reagents used. Palladium complexes with not only simple 77 -allylic moieties, but also cyclic derivatives, t/ -benzyls, 77 -allylic complexes derived from morphine alkaloids, and trialkyltin-subtituted T/ -allyls have been synthesized by oxidative addition of appropriate halides. Allyl carboxylates, especially acetates, are also common. When combined with other fimctionalities in the substrate, they lead to functionalized T/ -allylic Pd complexes. Examples of ester-substituted T/ -allyls obtained by reaction of the corresponding allylic trifluoroacetates 88 have been reported. Palladium complexes that bear an 7 -allyl with a pendant 2-pySiMc2-, where the py group coordinates to Pd, have been prepared from the corresponding allylic acetates 89. Allyl carbonates are also commonly used both in the stoichiometric preparation of -allylic complexes and in catalytic reactions that proceed through Pd -allylic intermediates. ... 

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