Lewis acid-catalyzed reactions allyltrimethylsilane

As a Carbon Nucleophile in Lewis Acid-Catalyzed Reactions. Allyltrimethylsilane is an alkene some 10 times more nucleophilic than propene, as judged by its reactions with di-arylmethyl cations. It reacts with a variety of cationic carbon electrophiles, usually prepared by coordination of a Lewis acid to a functional group, but also by chemical or electrochemical oxidation, or by irradiation in the presence of 9,10-dicyanoanthracene. The electrophile attacks the terminal alkenic... 

Lewis acid-catalyzed reaction of allyltrimethylsilane with 3-iodo-2-methoxyoxepane 19 leads to the ring opening however, under similar conditions, 3-bromo-2-(/>-nitrobenzyloxy)oxepane 20 gives 2-allyl-3-bromooxepane 21, as the single diastereomer of unknown configuration in 74% yield (Scheme 8) <1998TL2759>. 

Modified Sakurai reaction.- The original reaction involved the TiCU-catalyzed addition of allyltrimethylsilane to aldehydes and ketones or the acetals and ketals to form homoallylic alcohols or ethers (7,370-371). Marko et al. have extended this reaction to a synthesis of homoallylic ethers by a Lewis acid catalyzed reaction of allyltrimethylsilane with a carbonyl compound and a trimethylsilyl ether. 

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. 

Since acetals are more reactive than the corresponding carbonyl compounds under Lewis acid-catalyzed conditions, alkyl transfer reaction of acetals provides alkylated ethers in high yield. Recently, combined use of AlBrs/MesAl (10 1) and CuBr was reported as an excellent catalytic system for allylation reactions of dimethyl acetals with allyltrimethylsilane (Scheme 6.34) [40]. Catalytically active species are believed to be a mixed Al-Cu species. MesAl acts as a desiccant scavenging harmful HBr from the reaction mixture. 

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... 

Indolizidine alkaloids. The key step in a new stereocontrolled synthesis of these alkaloids, such as castanospermine (5), depends upon the diastereoselective reaction of an azagluco aldehyde with allylmetal reagents catalyzed by Lewis acids (12, 21-22). Thus reaction of allyltrimethylsilane with the aldehyde 1 and TiCL, (excess) in CH2C12 at - 85° results in the product 2, formed by selective chelation of the ot-amino aldehydo group with TiCl4. The product can be converted into 5... 

The reaction of isoxazolidin-5-ols and their methoxy and acetoxy derivatives with allyltrimethylsilane catalyzed by Lewis acids such as TMSOTf and BF3 OEt2 afforded the corresponding 5-allylisoxazolidines in high yields (Equation 62) <1998SL979>. 

An example of attaching a carbon nucleophile to an o, j8-unsaturated ketone is the Sakurai reaction. This involves the reaction of allyltrimethylsilane with an a,fi-unsaturated ketone to form a -unsaturated ketone in the presence of a Lewis acid. Howarth used indium(iii) chloride to catalyze this reaction in the ionic liquids [BMIM][BF4] and [BMIM][PF6] [207]. An example ofthis is shovm in Scheme 5.2-83. 

Reaction with Allylic Halides, Alcohols, and their Derivatives. Allylation of allyl and propargyl trimethylsilyl ethers as well as benzyl and propargylic alcohol derivatives proceeds in the presence of a catalytic amount of Lewis acids, such as ZnC, TMS(OTf), and B(C6F5)3. Direct substitutions of the hydroxyl group of allylic, ben-zylic, and propargylic alcohols are catalyzed by HN(S02F)2, a rhenium-oxo complex, and InCls (eq 27). A combination of chlorodimethylsilane and allyltrimethylsilane effectively promotes the deoxygenative allylation of aromatic ketones in the presence of a catalytic amount of an indium compound, such as indium trihalide or metallic indium (eq 28). Allylation of cyclic allylic acetates with allyltrimethylsilane can be catalyzed by molecular iodine. ... 

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