Ketones allyltrimethylsilane

Lithium-Ammonia, 158 Potassium hydride, 257 Tetrakis(triphenylphosphine)palla-dium(O), 289 Tributyltin chloride, 315 8,e-Unsaturated aldehydes and ketones Allyltrimethylsilane, 11 Lead tetraacetate, 155 Unsaturated amides Bis(benzonitrile)dichloropalladium(II), 34... 

Dimethyl acetals of aldehydes and ketones, for example benzaldehyde dimethyl acetal 121, and hemiacetals, react with allyltrimethylsilane 82 at -78 °C in CH2CI2, in the presence of TMSOTf 20 [169], trimethyhodosilane TIS 17 [159, 170],... 

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]... 

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... 

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

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. 

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. 

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. 

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

Nevertheless, the use of chirally modified Lewis acids as catalysts for enantioselective aminoalkylation reactions proved to be an extraordinary fertile research area [3b-d, 16]. Meanwhile, numerous publications demonstrate their exceptional potential for the activation and chiral modification of Mannich reagents (generally imino compounds). In this way, not only HCN or its synthetic equivalents but also various other nucleophiles could be ami-noalkylated asymmetrically (e.g., trimethylsilyl enol ethers derived from esters or ketones, alkenes, allyltributylstannane, allyltrimethylsilanes, and ketones). This way efficient routes for the enantioselective synthesis of a variety of valuable synthetic building blocks were created (e.g., a-amino nitriles, a- or //-amino acid derivatives, homoallylic amines or //-amino ketones) [3b-d]. 

Several methods promoted by a stoichiometric amount of chiral Lewis acid 38 [51] or chiral Lewis bases 39 [52, 53] and 40 [53] have been developed for enantioselective indium-mediated allylation of aldehydes and ketones by the Loh group. A combination of a chiral trimethylsilyl ether derived from norpseu-doephedrine and allyltrimethylsilane is also convenient for synthesis of enan-tiopure homoallylic alcohols from ketones [54,55]. Asymmetric carbonyl addition by chirally modified allylic metal reagents, to which chiral auxiliaries are covalently bonded, is also an efficient method to obtain enantiomerically enriched homoallylic alcohols and various excellent chiral allylating agents have been developed for example, (lS,2S)-pseudoephedrine- and (lF,2F)-cyclohex-ane-1,2-diamine-derived allylsilanes [56], polymer-supported chiral allylboron reagents [57], and a bisoxazoline-modified chiral allylzinc reagent [58]. An al-lyl transfer reaction from a chiral crotyl donor opened a way to highly enantioselective and a-selective crotylation of aldehydes [59-62]. Enzymatic routes to enantioselective allylation of carbonyl compounds have still not appeared. 

Aldehydes, ketones, and acetals react with allyltrimethylsilane in the presence of a catalytic amount of BiX3 (X = C1, Br, OTf) to give homoallyl alcohols or homoallyl alkyl ethers (Equation (52)).91-93 The BiX3-catalyzed allylation of aldehydes and sequential intramolecular etherification of the resulting homoallylic silyl ethers are involved in the stereoselective synthesis of polysubstituted tetrahydropyrans (Equation (53)).94,95 Similarly, these Lewis acids catalyze the cyanation of aldehydes and ketones with cyanotrimethylsilane. When a chiral bismuth(m) catalyst is used in the cyanation, cyanohydrines are obtained in up to 72% ee (Equation (54)). a-Aminonitriles are prepared directly from aldehydes, amines, and cyanotrimethysilane by the BiCl3-catalyzed Strecker-type reaction. 

A combination of chlorodimethylsilane and allyltrimethylsilane effectively promotes the deoxygenative allylation of aromatic ketones to terminal alkenes in the presence of a catalytic amount of InCl3 (Equation (94)). The choice of solvent is important the reaction of acetophenone proceeds only in dichloromethane or 1,2-dichloroethane. Aldehydes and aliphatic ketones give complicated mixtures. 

Titanium(lV) is a powerful but selective Lewis acid which can promote the coupling of allylsilanes with carbonyl compounds and derivatives. In the presence of titanium tetrachloride, benzalacetone reacts with allyltrimethylsilane by 1,4-addition to give 4-PHENYL-6-HEPTEN-2-ONE. Similarly, the enol silyl ether of cyclopentanone is coupled with f-pentyl chloride using titanium tetrachloride to give 2-(tert-PENTYL)CYCLOPENTANONE, an example of a-tert-alkylation of ketones. 

Chiral homoaXlylic alcohols. The chiral acetals 2 formed from an aldehyde and 1, undergo titanium-catalyzed coupling with allyltrimethylsilane with marked stereoselectivity. Highest stereoselectivity is usually obtained with the mixed catalyst TiCl4-Ti(0-/-Pr)4 (6 5). Cleavage of the chiral auxiliary, effected by oxidation to the ketone followed by P-elimination, provides optically active alcohols (4) with —95% ee (equation I).1... 

Regioselective Peterson reaction. Aldehydes react with the anion of an (a-al-koxy)allyltrimethylsilane (1) at both a- and y-positions. Addition of HMPT favors reaction at the y-position, whereas addition of Ti(0-/-Pr)4 (1 equiv.) results in exclusive reaction at the a-position to give an (E)-l, 3-dienol ether (2). These products are readily hydrolyzed to vinyl ketones (3).4... 

SnCU is also the principal source of alkyltin chlorides, R SnCl4 [51]. Allyltrialkyl-tin reagents react with SnCU to produce allyltrichlorotin species through an Se2 pathway (Eq. 32) [52-56], Allyltrimethylsilanes react with SnCU to produce the corresponding allyltrichlorotin (Eq. 33) [57]. Silyl enol ethers react with SnCU to give a-tri-chlorotin ketones (Eq. 34) [58]. Transmetalation or metathesis reactions of this type... 

The asymmetric allylation of unfunctionalized aliphatic ketones has also been described (Scheme 10-23) [43]. Simple aliphatic ketones are treated with a mixture of the trimethylsilyl ether of norpseudoephedrine (58), two equivalents of allyltrimethylsilane, and a catalytic amount of triflic acid. The homoallylic ethers... 

In the presence of excess acetyl halide and a tin(II) catalyst aromatic acetals react with allyltrimethylsilane to give a-allylbenzyl halides in good yield by double substitution of the acetal alkoxy groups (Scheme 10.127) [365]. The indium-catalyzed tandem reaction using a hydrosilane-allylsilane system enables deoxygenative allylation of aromatic ketones [366]. 

The use of C2-symmetric 1,2- and 1,3-diols as chiral auxiliaries is a reliable method for asymmetric allylation of acetals [382]. Acyclic acetals derived from homochiral 1-phenylethanol undergo the Hosomi-Sakurai allylation with high diastereoselectivity [383]. Tietze et al. have, on the other hand, reported that the TMSOTf-catalyzed successive acetalization-allylation reaction of aliphatic aldehydes with homochiral silyl ethers 123 and allyltrimethylsilane gives the corresponding homoallyl ethers with complete diastereocontrol these ethers can be readily converted into enantiomerically pure homoallyl alcohols without epimerization (Scheme 10.135) [384]. This method is applicable to asymmetric allylation of methyl ketones [385]. 

The allylation and cyanation of aldehydes and ketones are mediated by BiCl3 and BiBr3 [174, 175]. When a chiral bismuth(lll) catalyst is used for cyanation, cyanohydrins are obtained in up to 72% ee (Scheme 14.85) [175]. The Bi(OTf)3-promoted intramolecular Sakurai cyclization of homoallylic alcohols is involved as a key step in the stereoselective synthesis of polysubstituted tetrahydropyrans (Scheme 14.86) [176]. In the presence of the BiCl3-xMl binary catalyst, allyltrimethylsilane [177] and silyl enolates [178] are acylated to give aUyl ketones and /l-dikelories, respectively. 

The titanium tetrachloride-promoted addition of allyltrimethylsilane to methylcyclohexenones and methylcycloheptenones has been explored (68,69) results are summarized in Eqs. [l]-[6] of Scheme 32. With the exception of 4-substituted cyclohexenones and cycloheptenones, good to excellent facial selection is observed (Eqs. [2], [5], and [6], Scheme 32). The major products obtained are those predicted by axial attack of the nucleophile on the more stable conformer of the acceptor. Although there are some similarities, the results show some significant deviations from the corresponding cuprate additions. Addition to the bicyclic enone 32.1 occurs from the convex face, producing exclusively the cis-fused decalone (Eq. [7], Scheme 32) (5). In this case, the product is formally the result of equatorial attack of the allylsilane on the a,/ -unsaturated ketone. 

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