Allylations allyltrimethylsilane

Treatment of 2-methoxy-l-tert-butoxycarbonylpiperidine (127) with allyltrimethylsilane and TiCU gave a mixture of 2-allyl-l-rerr-butoxycarbo-nylpiperidine (128) and 3-[(trimethylsilyl)methyl]perhydropyrido[l,2-c][l,3] oxazin-l-one (129) (97JCS(P1)2163). 

The direct allylation of 2-phenylpropanal proceeds with much lower selectivity [2-propenylmagnesium bromide 73 27 allyltrimethylsilane/titanium(IV) chloride 67 33]27. 

Recently, Co(III)-allyl complexes have been described to be sulfonylated regiospecifi-cally by sulfonyl halides under irradiation232 (equation 42). Similarly, allyl methyl sulfone has been obtained from allyltrimethylsilane under copper(I) catalysis213. 

In the presence of catalytic amounts of TMSOTf 20 methyl pyruvate reacts with N,N-bis(trimethylsilyl)formamide 22c in CCI4 to give the silylated 0,N-acetal 433 in 83% yield ]44] this, with allyltrimethylsilane 82 and excess TMSOTf 20, after 30 h at 78 °C in CH2CI2, affords 72% of the methyl ester of 2-allyl-N-formylala-... 

Phenylpropanal 583 reacts with phenylthiotrimethylsilane 584 in the presence of TiCl4, via the 0,S-acetal 585, to give the S,S-acetal 586 [144]. Conducting the reaction in the presence of allyltrimethylsilane 82 and SnCl furnishes the allylic sulfides 587 and 588 in 3 1 ratio and 56% yield [144] (Scheme 5.45). 

Benzaldehyde dimethyl acetal 121 reacts, for example, with the silylated allylic alcohol 645, in the presence of SnCl2-MeCOCl, via an intermediate analogous to 641, to the 3-methylenetetrahydrofuran 646 and methoxytrimethylsilane 13 a [182], whereas benzaldehyde dimethyl acetal 121 reacts with the silylated homoallylalco-hol 640 in the presence of TMSOTf 20 to afford exclusively the ds 4-vinyltetrahy-drofuran 647 and 13 a [183]. A related cyclization of an a-acetoxy urethane 648 containing an allyltrimethylsilane moiety gives the 3-vinylpyrrohdine 649 in 88% yield and trimethylsilyl acetate 142 [184, 185]. Likewise, methyl 2-formylamido-2-trimethylsilyloxypropionate reacts with allyltrimethylsilane 82 or other allyltri-methylsilanes to give methyl 2-formamido-2-aUyl-propionate and some d -unsatu-rated amino acid esters and HMDSO 7 [186] (Scheme 5.56). 

The weaker Lewis add TMSOTf 20 as catalyst gives, after 2 h at 0°C in CH2CI2, a 20 80 mixture of 805 and 806 in only 23% yield (Scheme 6.8). But this yield will probably increase either on longer reaction time at 0°C or on shorter reaction time at 25 °C On replacing one of the methyl groups in 804 by an acetylene substituent the resulting enyne adds allyltrimethylsilane 82 or anisole in the presence of TMSOTf 20 to give allenes [18]. Substituted allyltrimethylsilanes such as 808 react with the allylic silylether 807 after 70 h at 25 °C in 62% yield to a 41 59 mixture of 809 and 810 as well as 7 [17]. Closely related additions of 82 to allylic ethers or O-acetates are discussed in Refs. 17a-c. 

Because allyltrimethylsilane 82 or benzyltrimethylsilane 83 can be regarded as combinations of the hard trimethylsilyl cation and the soff allyl or benzyl anions, pyridine N-oxide 860 reacts with excess 82 or 83 in the presence of catalytic amounts of tetrabutylammonium fluoride di- or trihydrate in THF to give 2-allyl-or 2-benzylpyridines 948 and 950 [60]. The general reaction of silicon reagents such as 82 and 83 or of trimethylsilyl cyanide 18 with fluoride to generate allyl or... 

Matrix IR spectra of various silenes are important analytical features and allow detection of these intermediates in very complex reaction mixtures. Thus, the vibrational frequencies of Me2Si=CH2 were used in the study of the pyrolysis mechanism of allyltrimethylsilane [120] (Mal tsev et al., 1983). It was found that two pathways occur simultaneously for this reaction (Scheme 6). On the one hand, thermal destruction of the silane [120] results in formation of propylene and silene [117] (retroene reaction) on the other hand, homolytic cleavage of the Si—C bond leads to the generation of free allyl and trimethylsilyl radicals. While both the silene [117] and allyl radical [115] were stabilized and detected in the argon matrix, the radical SiMc3 was unstable under the pyrolysis conditions and decomposed to form low-molecular products. 

Si. rra(pentafluorophenyl)boron was found to be an efficient, air-stable, and water-tolerant Lewis-acid catalyst for the allylation reaction of allylsilanes with aldehydes.167 Sc(OTf)3-catalyzed allylations of hydrates of a-keto aldehydes, glyoxylates and activated aromatic aldehydes with allyltrimethylsilane in H2O-CH3CN were examined. a-Keto and a-ester homoallylic alcohols and aromatic homoallylic alcohols were obtained in good to excellent yields.168 Allylation reactions of carbonyl compounds such as aldehydes and reactive ketones using allyltrimethoxysilane in aqueous media proceeded smoothly in the presence of 5 mol% of a CdF2-terpyridine complex (Eq. 8.71).169... 

Lewis acids are also effective to induce the nucleophilic substitution of allylic nitro compounds. These compounds react with allyltrimethylsilane,28 silyl enolates,28 or cy-anotrimethylsilane29 in the presence of SnCl4 to give substitution products, respectively (see Eqs. 7.24-7.26). 

Jung and Maderna have reported the microwave-assisted allylation of acetals with allyltrimethylsilane in the presence of copper(I) bromide as promoter (Scheme 6.77b) [162]. Stoichiometric amounts of copper(I) bromide are required and the reaction works best with aromatic acetals free from strongly electron-withdrawing substituents on the aromatic ring. 

Miscellaneous Ketone Reductions. The reductive allylation of aromatic ketones occurs with the reagent combination of Me2ClSiH/allyltrimethylsilane/ InCl3 (Eq. 253).427... 

The alkylation of olefinic G-H bonds proceeds when conjugated enones are employed in the ruthenium-catalyzed reaction with alkenes, as shown in Equation (16).1 7 Among the acylcyclohexenes, 1-pivaloyl-l-cyclohexene exhibits a high reactivity and the presence of an oxygen atom at the allylic position in the six-membered ring increases the reactivity of the enones. Some terminal olefins, for example, triethoxyvinylsilane, allyltrimethylsilane, methyl methacrylate, and vinylcyclohexane, are applicable for the alkylation of the olefinic C-H bonds. Acyclic enones also undergo this alkylation. 

Alkoxycarbenium ion pool 26 was allowed to react with allyltrimethylsilane as a carbon nucleophile to give the corresponding allylated product 27. The success of the nucleophilic reaction also indicated the presence of the alkoxycarbenium ion in relatively high concentration in the solution. 

The thermal stability of the alkoxycarbenium ion is noteworthy. When the electrolysis was complete, the cation pool of 26 was allowed to warm up to a second temperature. After being kept there for 30 min, the cation was allowed to react with allyltrimethylsilane. The yield of allylated product 27 was plotted against the temperature. It can be seen from Fig. 7 that alkoxycarbenium ion 26 is stable at temperatures approximately below -50 °C. Above this temperature, the yield of 27 decreased significantly. Intramolecular coordination of ether functionality seems to be effective for the stabilization of alkoxycarbenium ions.33... 

The a-phenylthioether 28 was oxidized in the absence of a nucleophile by low temperature electrolysis (Scheme 15). The corresponding alkoxycarbenium ion pool 26 was formed, which exhibited a single set of signals in H and l3C NMR spectroscopy. The chemical shifts were quite similar to those obtained by the oxidative C-Si bond dissociation described in the previous section. Subsequently, the cation pool was allowed to react with allyltrimethylsilane to obtain the allylated product 27. 

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