Trans-3-trimethylsilyl allylic

Trans-1 -allyl-2-(trimethylsilyl)cyclopentane and trans-1 -allyl-2-(trimethylsilyl)-cyclohexane are formed from the reaction of la with cyclopentene and cyclohexene, respectively. A second allylsilylation reaction of these compounds with la also gives unusual allylsilylation products, 7-cyclopent-l-enyl-2,2-dimethyl-4-(trimethylsilyl-methyl)-2-silaheptane (30%) and 4-((cyclohex-l-enyl)methyl)-2,2,8,8-tetramethyl-2,8-disilanonane (39%). As observed in the allylsilylation of 4-(trimethylsilyl-methyl)-l-alkenes, these products are likely formed via intramolecular silyl rearrangements. In this case, the results strongly suggest that a 1,5-silyl shift and... 

The Claisen rearrangement has been used to prepare j8,y-unsaturated amides, largely as the E-isomers, from 3-(trimethylsilyl)allyl alcohols and amide acetals (Scheme 48). Overall yields and stereoselectivities are excellent. Conditions have been found under which the stereochemical outcome of the related ynamine-Claisen rearrangement can be controlled. Thus, the kinetically favoured intermediate is the E-enamine (140) which leads to the "trans product (142), whereas the Z-isomer (141) is thermodynamically favoured and gives the cw ... 

A seven-membered ring is formed in the cyclization of 195 (equation 95)105. The homologue 196 affords the fused cyclooctane 197, together with the cis- and trans-decalinones 198 (equation 96)106. Six-, seven- and eight-membered rings are produced in Lewis acid-catalysed reactions of various cyclohexenones with side-chains terminating in allylic trimethylsilyl groups (equations 97 - 99)107. 

Allyltrimethylsilane (la) reacts with cycloalkenes such as cyclohexene and cyclo-pentene at room temperature to give stereospecifically tra j -l-trimethylsilyl-2-al-lylcycloalkanes. These products are formed through trans addition and an allylic inversion. 

Notably, the asymmetric Claisen rearrangement of ci j-allylic ot-(trimethylsilyl)vinyl ethers with the chiral aluminum reagent produced optically active acylsilanes with the same absolute configuration as those from trans-allylic a-(trimethylsilyl)vinyl ethers (eq 5). ... 

The reactions were carried out using [Pd(/j -C3H5)Cl]2 as procatalyst in a mixture of dimethylmalonate, N,0-bis(trimethylsilyl)acetamide (BSA), and potassium acetate in methylene chloride (eq 2) Under these conditions (5)-dimethyl 1,3-diphenylprop-2-enylmalonate was isolated in 92% yield and 91% enantioselectivity. The stereochemical outcome was rationalized by reaction through transition state A, in which the nucleophile attacks the allylic terminus trans to the oxazoline nitrogen. 

Epoxidation of acyclic allyl alcohols with peracid and Mo/TBHP displays an opposite stereospecificity to that for the V/TBHP system. Trimethylsilyl-substituted allylic alcohols give t/zreo-epoxyalcohols with MCPBA and erythro-alcohols with VO(acac)a-TBHP, with high stereoselectivity. In the stereospecific epoxidation of cis- and trans-allyl alcohols, formation of a transition state is assumed with the development of two H bonds between the hydrogen atom of the hydroxy group of the allyl alcohol and the oxygen of the peracid, and between the hydrogen of the peracid OH and the oxygen of the ether 10. An analysis of the diastereometric transition-state interactions for stereoselective epoxidation of acyclic allylic alcohols has been published. A conformational effect may be responsible for the unexpected cis major product in Eq. 2. 

An important clue as to how this could be done came from work done by Henbest and coworkers [2]. This group compared the diastereoselectivity of peracid oxidation reactions of 3-hydroxy and 3-acyloxycyclohex-2-enes (Scheme 8.2). When the alcohol was capped by an acetate group, the trans addition product predominated. Better selectivity was later obtained by placing a larger trimethylsilyl group on the allylic alcohol [3]. In both cases, the source of the selectivity could be ascribed to the approach of the reagent from the least hindered side of the molecule anti to OR) put another way, the approach from one face was slowed relative to the other (Scheme 8.2a). 

Unique to E-vinyl derivatives of 9-BBN is their Grignard-like addition to aldehydes [6] to afford stereodefined alcohols. trans-E-Vinyl-9-BBN synthesis via dehydroborylation [7] process is extended to the synthesis of trans-2-tnmeth-ylsilyl vinylborane [8]. trans-2-Trimethylsilylvinyl-9-BBN adds cleanly to aldehydes (Eq. 6.17) to provide pure frans-3-trimethylsilyl(TMS) allylic alcohols in excellent yields (Table 6.18) [8]. ... 

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