2-Trimethylsilyl-l-alkenes

Z)-l-Trimethylsilyl-l-alkenes.1 The a-trimethylsilyl diazoalkanes (2), prepared by reaction of primary halides (1) with the lithium anion of trimethylsilyl diazomethane, decompose on treatment with rhodium(II) pivalate [superior in this case to rhodium(II) acetate] to (Z)-l-trimethylsilyl-1-alkenes. 

E)-l-Trimethylsilyl-l-alkenes.1 These alkenes can be prepared by reaction of the lithium anion (1) of trimethylsilyldiazomethane with primary alkyl halides followed by decomposition with CuCl (86-96% yield). (E)-2-Aryl-l-trimethylsi-lylethylenes are obtained directly by reaction of trimethylsilyldiazomethane with benzylsulfonyl chlorides and triethylamine. 

The vinylsilane-terminated cyclization strategy has been extended to the preparation of eight-membered cyclic ethers. Oxocenes (Scheme 17) with AAunsaturation (3,6,7,8-tetrahydro-2//-oxocins) were prepared efficiently by the SnCU-catalyzed cyclization of the mixed acetals (39) with complete re-giochemical control. Electrophilic addition on the 2-(trimethylsilyl)-l-alkene occurs predominanfiy at the terminal position of the alkene to form a tertiary a-silyl, rather than a primary 3-silyl, carbocation. The... 

Trimethylsilyl-l-alkenes. The lithium reagent is prepared from the corresponding selenide by treatment with BuLi. Its reaction with alkyl halides provides the allylsilanes. 

E)-l-Trimethylsilyl-l-alkenes are available by chloroplatinic acid catalysed hydrosilylation of 1-alkynes. These vinyl silanes react with dichloromethyl methyl ether in the presence of titanium(iv) chloride at low temperature to give a/S-unsaturated aldehydes. Alkenyl silanes with the silyl group in a non-terminal position also give the corresponding a/8-unsaturated aldehyde (Scheme 50). " ... 

Synthesis of Allylsilanes. TMSCu reacts with a variety of allylic substrates to form allylsilanes stereoselectively and in good to excellent yields. Thus the reagent reacts readily with primary allylic halides, " sulfonates from secondary and tertiary alcohols, and primary and secondary allylic phosphates to yield a variety of allylsilanes. Representative examples of these reactions are shown in eqs 1-3. This methodology seems particularly attractive for the S3Uithe-sis of 3-trimethylsilyl-l-alkenes which are presently unavailable... 

The reactions of TMSCu are in marked contrast to the reactions of trimethylsilyllithium with similar substrates. Whereas treatment of a l-chloro-2-alkene with TMSCu affords a 3-trimethylsilyl-l-alkene, reaction of TMSLi with these same starting materials yields terminal ( )-aUylsilanes where the stereochemistry of the double bond is retained in the product (eq 7). Thus a single allylic halide yields either of two regioisomers by proper choice of reaction conditions. With aUyUc phosphates, TMSCu affords as major product the aUylsUane resulting from attack by what is formally an SN2 -like reaction. With TMSLi, however, the major product is always the isomeric allylsilane having a more substituted internal double bond (eq 8). 

Reactions of 3-methylthio-4-trimethylsilyl-l,2-butadiene with electron-poor monosub-stituted and disubstituted alkenes were promoted by a catalytic amount of ethylaluminum dichloride, affording the corresponding methylenecyclobutanes with high selectivities and with yields ranging from 37% for methyl crotonate to 97% for methacrylonitrile15. 

Electron-rich 3-methoxy-4-trimethylsilyl-l,2-butadiene (22) reacted with several electron-poor alkenes in the presence of diethylaluminum chloride to afford methylene cyclobutanes 23. Reactions with alkynes were performed in the presence of methylalu-minum bis(2,4,6-tri-t-butylphenoxide) (equation 7)16. 

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... 

From singlet oxygen reaction with silyl enol ethers When a carbon tetrachloride solution of 1-methoxy-l-trimethylsiloxy-l-alkene in the presence of tetraphenylporphyrin and bubbling oxygen is irradiated with a 400-W Na lamp, a-trimethylsilyl peroxyesters were obtained in good yield (equation 11) . ... 

Thermolysis of 2-diazo-l,3-dithiane, prepared in situ from the reaction of 2-lithio-2-trimethylsilyl-l,3-dithiane and tosyl azide, occurs already below 0°C. The resulting carbene dimerizes efficiently even in the presence of alkenes and alkynes to give bis(l,3-dithianylidene) in 78% yield (Scheme 41) <1997T9269>. 

Hydroxy- bzw. 2-Mercapto-imidazolc allgemeine Arbeitsvorschrift122 0,05 mol l,2-Bis-[trimethylsilyl-oxy]-l-alken werden mit 0,2 mol Harnstoff oder Thioharnstoff und 0,5 ml 2,5 M Salzsaure in 25 ml Cy-clohexanol 3h bei 160° gcriihrt. Dann wird filtriert, das Losungsmittel abdestilliert und der Riickstand aus Ethanol/Wasser umkristallisiert. 

Allylsilylation is an addition reaction of allylorganosilanes to carbon-carbon multiple bonds of unsaturated hydrocarbons in the presence of Lewis acids.13 Common examples of unsaturated hydrocarbons for allylsilylations include alkenes,2 cycloalkenes,13,2 allyltriorganosilanes,13,2,11 13 5-(trimethylsilyl)-l-pent-enes,13 diallylsilanes,12,16 conjugated dienes,13 and alkynes.19 21... 

Furanes.3 Hydromagnesiation of 3-trimethylsilyl-2-propyne-l-ol (1) (11, 163) followed by reaction with an aldehyde or ketone provides E-3-trimethylsilyl-2-alkene-l,4-diols (2). These are converted into 3-trimethylsilyl-2,5-dihydrofuranes (3) on dehydration... 

Table 11. 1-[l-(Trimethylsilyl)cyclopropyl]alkenes from Ketones and a-Bromovinyltrimethylsilane (Method A) or l-Bromo-l-(trimethylsilyl)cyclopropene (Method B) ... 

Introduction of an alkylthio group on the allene system increased the reactivity of the allene moiety in [2 + 2] cycloaddition reactions. It proved possible to conduct reactions of this allene at much lower temperatures. By adding Lewis acids, the reaction temperature could be decreased even more, as was illustrated by the Lewis acid catalyzed [2-1-2] cycioadditions of l-trimethylsilyl-l-methylthio-l,2-propadiene with a variety of electron-poor alkenes, including cyclic and non-cyclic enones, acrylates, methyl fumarate and acrylonitrile. When a chiral diol 21 based titanium catalyst was employed, the [2-1-2] cycloaddition reactions of /-acryloyl-l,3-oxazolidin-2-ones 17a and 17b with allenyl sulfides 18 yielded methylenecyclobutanes 19 and 20 with high optical purities (equation The highest yields were obtained with electron-poor allenophile 17b. 

Bromo-l-alkenes. Hydrogen bromide adds to terminal acetylenes to form 1-bromo-l-alkenes. However, it adds to 1-trimethylsilyl-l-alkynes to form 2-bromo-l-alkenes. Although the reaction is a free radical reaction, a peroxide initiator is not required and may be deleterious. Trimethylsilyl bromide is the... 

Telrastthstituted alkenes. Melhy]magnesium bromide in THF-benzenc adds to l-trimethylsilyl-l-octyne in the presence of a catalytic amount of this nickel compound and trimethylaluminum (1 1) to give the vinyl Grignard reagent 2,... 

Optically active fiirfiiryl alcohols and hydroxy butenolides of the following type were prepared from /nms-l-trimethylsilyl-i-alken-l-ynes by successive asymmetric dihydroxylation and hydromagnesi-ation reactions <93TL 4975>. 

Hydroboration of Silylalkenes and SUylalkynes. (Z)-l-Trimethylsily 1-1-alkenes react with DBBS to produce ge/rniime-talloalkanes, which upon oxidation afford alcohols containing the trimethylsilyl group in high yields (72-84%) (eq 13). Unexpectedly, desilylation of (2)-2-(l-trimethylsilyl-l-hexenyl)dibromo-borane is observed during the hydrolysis followed by treatment with 1,3-propanediol. 

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