Allyltrimethylsilane, -type

Only recently a selective crossed metathesis between terminal alkenes and terminal alkynes has been described using the same catalyst.6 Allyltrimethylsilane proved to be a suitable alkene component for this reaction. Therefore, the concept of immobilizing terminal olefins onto polymer-supported allylsilane was extended to the binding of terminal alkynes. A series of structurally diverse terminal alkynes was reacted with 1 in the presence of catalytic amounts of Ru.7 The resulting polymer-bound dienes 3 are subject to protodesilylation (1.5% TFA) via a conjugate mechanism resulting in the formation of products of type 6 (Table 13.3). Mixtures of E- and Z-isomers (E/Z = 8 1 -1 1) are formed. The identity of the dominating E-isomer was established by NOE analysis. 

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. 

A [3+3]-type annulation between a,a -dimethoxylated lactam 43 and allyltrimethylsilane gives bicyclic lactam 44. The reaction proceeds presumably through the allylation at the a-position followed by the intramolecular addition of the cation developed at the a -position to the allylic double bond (85JOC3243). The aza-Diels-Alder reaction of... 

The addition of BF3 OEt2 to a solution containing Ph3BiF2, allyltrimethylsilane and excess arenes induces a Friedel-Crafts-type allylation at low temperatures to yield allylarenes [36]. Benzene, toluene, anisole, p-xylene, and p-dimethoxyben-zene were all allylated with ease to give the corresponding allylation products, although diallylation could not be suppressed in the reaction with electron-rich... 

The stereoisomers 16c and 16d have also been prepared by a [3 + 3]-type annelation between a,a -dimethoxylated amides and allyltrimethylsilane (363). Compound 366 was synthesized by ring formation with 363 and 365, prepared by methoxymethylation of 364, in the presence of TiCl4. Hydrogenation of 366 foWov/ed by bulylalion with n-BuLi and reduction with sodium borohy dride gave a mixture of stereoisomers 16c and 16d (Scheme 41) (437). 

Piperidine skeletons are easily prepared by utilizing a unique [3 + 3]-type annela-tion between allyltrimethylsilane and a,oc -dimethoxylated amides which are easily... 

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. 

Although the second type using other traditional Lewis acids, for example BF3 OEt2 and TiCU, has been described by several groups [42], there are few examples employing la and other silicon Lewis acids. Marko and coworker extended their SMS reaction to the diastereoselective version [37]. According to one scheme illustrated in that paper, trimethylsilyl ethers of chiral 1-arylethanol were examined to afford diastereoselectivity in an allylation of allyltrimethylsilane and cyclohexanecar-boaldehyde (Sch. 11). A diastereomeric ratio of up to 10 1 was achieved at lower temperatures. 

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... 

Another type of convertible nucleoside phosphoramidite, a derivative of (5 S)-5 -C-(5-bromo-2-penten-l-yl)-2 -deoxyribosylfuranosyl thymidine (49), has been reported. The synthesis of this phosphoramidite was stereoselective and involved a Sakurai reaction between 5 -C-thymidine aldehyde and allyltrimethylsilane. Seela has reported the synthesis of the ribosyl-phosphoramidite derivatives of 7-bromo- and 7-iodo-8-aza-7-deazapurine-2,6-diamine (50a,b) from advanced synthetic precursors and of the bromo- and iodo-derivatives at the 5-position of uracyl phosphoramidite (51a,b). He further described the effect on base-pair stability due to their incorporation into oligonucleotide duplexes. ... 

In the reactions of Type II allylmetal reagents with chiral aldehydes, y -alkoxy substituents on the aldehyde can exert a strong influence on the reaction, much more so than in reactions of Type I allylmetal reagents. Reetz and co-workers reported that the BF3-OEt2-catalyzed allylation reaction of the /f-benzyloxy aldehyde 130 with allyltrimethylsilane 131 is selective for the, 3-anti diol 132 (Eq. (11.7)) [92]. Evans and co-workers sub.sequently rationalized this result by invoking tran-... 

Iodine transfer addition to allyltrimethylsilane provides a more environmentally friendly alternative to allyltributylstannane. In these allylations, which are exemplified in Scheme 6, the initially formed I-transfer product undergoes spontaneous loss of TMSI to generate the observed allylation product. Guindon has shown that allylation of the Lewis acid complexes of ) -alkoxy esters in this manner can lead to products with high anti stereoselectivity [22]. It is also believed that the presence of Lewis acids enhances the electrophilicity of the radical. Allylations of this type can also prove successful when Br-transfcr or PhSe-transfer reactions are employed. 

Jeffery, T. (2000) Tetraalkylammonium salt-based catalyst systems for directing Heck-type reactions. Arylation of allyltrimethylsilane. Tetrahedron Lett., 41, 8445-9. 

Smith and coworkers next extended Type II ARC domino protocol beyond dithiane arena by designing a variety of effective ARC linchpins with different ASGs capable of three and four component couplings. In their first effort toward this goal, they developed readily available 2-bromoallylsilane [62a], and subsequently, allyltrimethylsilane 185 [63], and recently o-TMS (trimethylsilyl) benzaldehyde 188 as promising linchpins for Type II ARC process [64, 65]. However, domino anionic relay reactions with these linchpins 185 and 188 are not discussed in this chapter, since they are not initiated by nucleophilic substitution as the first step. 

Parallel chemistry is observed with the trimethylene methane complexes 10.136 (Scheme 10.34)." In this case, however, the cationic tv -complex 10.137, although observable by NMR at low temperature," cannot be isolated. It could be trapped with nucleophiles, but different nucleophiles gave different types of product. Allyltrimethylsilane gave a new trimethylene methane complex 10.138," while methanol yielded an if -diene complex 10.139. The different structural types produced, trimethylene methane versus diene complex, are likely to be due to kinetic and thermodynamic control as addition of methanol would be expected to be reversible under acidic conditions. 

Michael addition of allyltrimethylsilane to a-nitro-olefins in the presence of aluminium chloride gives, following a Nef-type reaction, y,5-unsaturated... 

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