Ethers Allyltrimethylsilane

Acetonylation.1 In the presence of TiCl or BF3 etherate allyltrimethylsilane undergoes conjugate addition to a,/ -enones. The 5,e-enones formed are converted by ozonation or KMnO K 10 to o-keto aldehydes. Wacker oxidation can be used to obtain methyl ketones. 

Cerium(IV) ammonium nitrate, 67 Dimethyl sulfate, 239 Other ethers Allyltrimethylsilane, 11 Benzyl trichloroacetimidate, 32 (E)-(Carboxyvinyl)trimethylammonium betaine, 67... 

Allyltributyltin, 10 Vinyltrimethylsilane, 343 Homoallylic ethers Allyltrimethylsilane, 11 Crotyltrimethylsilane, 86 Trityl perchlorate, 339 Homopropargylic alcohols Allenylboronic acid, 36 D imethoxy [ 1 -trimethylsilyl-1,2-buta-dienyljborane, 218 Lithium acetylide, 44 Triisopropoxy[l-(trimethylsilyl)-l,2-buta-dienyl]titanium, 218 Hydroperoxides Oxygen, singlet, 228 Hydroxy acids a-Hydroxy acids... 

A mixture of TMSOTf (0.1 mmol, lmol%), allyltrimethylsilane (11.5 mmol) and dichioromethane (1 ml) was cooled to -78 °C, and to this was added benzaldehyde dimethylacetal (10.5 mmol) in dichioromethane (4ml). The resulting mixture was stirred for 6h at —78°C, and then poured into saturated sodium hydrogen carbonate solution (10 ml) and extracted with ether (3 x 20 ml). The combined organic extracts were washed with brine, dried and concentrated. Chromatography on silica gel (1 20 ether hexane) gave 4-pheny]-4-methoxybut-l-ene (9.2mmol, 88%). 

Additions of silylated ketene acetals to lactones such as valerolactone in the presence of triphenylmethyl perchlorate in combination with either allyltrimethylsilane 82, trimethylsilyl cyanide 18, or triethylsilane 84b, to afford substituted cyclic ethers in high yields have already been discussed in Section 4.8. Aldehydes or ketones such as cyclohexanone condense in a modified Sakurai-cyclization with the silylated homoallylic alcohol 640 in the presence of TMSOTf 20, via 641, to give unsaturated cyclic spiro ethers 642 and HMDSO 7, whereas the 0,0-diethyllactone acetal 643 gives, with 640, the spiroacetal 644 and ethoxytrimethylsilane 13b [176-181]... 

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. 

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... 

For the addition of ethylene, EtOAc as solvent was particularly advantageous and gave 418 in 60% yield (Scheme 6.86). The monosubstituted ethylenes 1-hexene, vinylcyclohexane, allyltrimethylsilane, allyl alcohol, ethyl vinyl ether, vinyl acetate and N-vinyl-2-pyrrolidone furnished [2 + 2]-cycloadducts of the type 419 in yields of 54—100%. Mixtures of [2 + 2]-cycloadducts of the types 419 and 420 were formed with vinylcyclopropane, styrene and derivatives substituted at the phenyl group, acrylonitrile, methyl acrylate and phenyl vinyl thioether (yields of 56-76%), in which the diastereomers 419 predominated up to a ratio of 2.5 1 except in the case of the styrenes, where this ratio was 1 1. The Hammett p value for the addition of the styrenes to 417 turned out to be -0.54, suggesting that there is little charge separation in the transition state [155]. In the case of 6, the p value was determined as +0.79 (see Section 6.3.1) and indicates a slight polarization in the opposite direction. This astounding variety of substrates for 417 is contrasted by only a few monosubstituted ethylenes whose addition products with 417 could not be observed or were formed in only small amounts phenyl vinyl ether, vinyl bromide, (perfluorobutyl)-ethylene, phenyl vinyl sulfoxide and sulfone, methyl vinyl ketone and the vinylpyri-dines. 

The first procedure is a one-pot sequential process in which the acetal is formed from the aldehyde in a Bi(OTf)3-catalyzed reaction with trialkylorthoformate and the corresponding alcohol. After the aldehyde was consumed, the remaining alcohol was removed under reduced pressure. Acetonitrile, allyltrimethylsilane, and additional Bi(OTf)3 were added and the desired homoallyl ethers were obtained in moderate to good yields (Scheme 10). 

A three-component one-pot procedure was also developed. This method involves stirring the aldehyde, trialkylorthoformate, and allyltrimethylsilane in CH3CN in the presence of a catalytic amount of Bi(OTf)3. The homoallyl ethers were again obtained in moderate to good yields with a more simple and straightforward procedure (Scheme 11). 

Carbon-carbon ternary centers can also be assembled by nucleophilic addition. Manfred Braun of the Universitat Diisseldorf has devised (Angew. Chem. bit. Ed. 2004,43,514) the Lewis acidic Ti complex 8. Exposure of a racemic benzylic silyl ether such as 7 to allyltrimethylsilane in the presence of the catalyst 8 leads to the alkylated product 9. Racemic tertiary benzylic ethers are also converted to the alkylated quaternary centers in > 90% . 

Monocyanohydrins of P-diketones.3 In the presence of TiCl4, acetyl cyanide reacts with enol silyl ethers of ketones at - 78° to afford monocyanohydrins of diketoncs in excellent yield. The corresponding reaction with enol silyl ethers aldehydes proceeds in only about 35% yield. A low temperature is essential for this reaction. A similar reaction is possible with allyltrimethylsilane. 

Homoallyl ethers. Trimethylsilyl triflate catalyzes a reaction between dimethyl ketals and allyltrimethylsilane to form homoallyl ethers. Allylation is not possible with the parent ketones. 

SILYLATION Allyltrimethylsilane. Bistri-methylsilyl ether. 4-0-ButyldimethyE siiyloxy-3-pen tene-2-one. r-B u ty ldi-methyisilyl irifluoromethanesulfonate. Chloromethyldiphenylsilane. Chlorotrl-methylsilane. Hexamethyldisiloxane. 

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