3- Trimethylsilyl- 1-alkene

Allyltrimethylsilanes. Trimethylsilyllithium reacts with primary (E)-allylic halides to form the corresponding allyltrimethylsilanes. Reaction of the reagent prepared from (CH,),SiLi and Cul in HMPT with these halides results in the isomeric 3-trimethylsilyl-1-alkene. ... 

On the contrary, the reaction of l-phenylthio-l-trimethylsilyl-2-propene 5257 with alkyllithium afforded the Z-l-phenylthio-l-trimethylsilyl alkenes 51 and the reaction of 1-methoxy-l-phenylthio-l-trialkylsilylalkanes 5458 provided a highly stereoselective synthesis of Z-l-phenylthio-l-trialkylsilylalkenes 53 (Scheme 35). 

This is ordinary electrophilic addition, with rate-determining protonation as the first step. Certain other alkynes have also been hydrated to ketones with strong acids in the absence of mercuric salts. Simple alkynes can also be converted to ketones by heating with formic acid, without a catalyst.Lactones have been prepared from trimethylsilyl alkenes containing an hydroxyl unit elsewhere in the molecule, when reacted with molecular oxygen, CuCla, and a palladium catalyst. ... 

Hodgson, D. M., Comina, P. J. Chromium(ll)-mediated synthesis of 1,1-bis(trimethylsilyl)alkenes from aldehydes and (Me3Si)2CBr2. Tetrahedron Lett. 1994, 35, 9469-9470. 

Two new classes of ligands, bicyclic phosphate 47 [45] and ferf-alkyl isonitriles [46] on palladium, enable bis-silylation with hexaalkyldisilanes, which have been regarded to be much less reactive than the activated disilanes (Eq. 20). Reactions of the terminal alkynes with hexamethyldisilane in the presence of these palladium catalysts afford (Z)-l,2-bis(trimethylsilyl)alkenes 48 in high yields. 

In-plane, backside, vinylic nucleophilic substitution of an appropriate halide leaving group can also be effected. Thus, the ( )-P-alkylvinyl(phenyl)iodonium salt, which can be prepared from the corresponding trimethylsilyl alkene and iodoso-benzene, undergoes both Sn2 substitution to produce the inverted chloroalkene and elimination to the corresponding alkyne (Scheme 7.11). 

Halo-1-lithium alkenes react with chlorotrimethylsilane in TMF/HMPT to form 1-halo-l-trimethylsilyl alkenes (Eq.3.31) ... 

Treatment of trimethylsilyldiazoalkanes, obtained by alkylation of diazo(trimethylsilyl)methyllithium with RCH2X, with copper(I) chloride gives excellent yields of ( )-l-trimethylsilyl-alkenes (eq 8). ... 

If alkyl groups are attached to the ylide carbon atom, cis-olefins are formed at low temperatures with stereoselectivity up to 98Vo. Sodium bis(trimethylsilyl)amide is a recommended base for this purpose. Electron withdrawing groups at the ylide carbon atom give rise to trans-stereoselectivity. If the carbon atom is connected with a polyene, mixtures of cis- and rrans-alkenes are formed. The trans-olefin is also stereoseiectively produced when phosphonate diester a-carbanions are used, because the elimination of a phosphate ester anion is slow (W.S. Wadsworth, 1977). 

The trimethylsilyl group has been used to prepare stable aci-nitro esters and these react with alkenes to produce intermediate isoxazolidines which were readily converted into 2-isoxazolines (Scheme 119) (73ZOB1715, 74DOK109, 78ACS(B)ll8>. 

A newer method for the preparation of nitronic esters, namely utilizing the (9-trimethyl-silyl ester, has been reported and these are prepared by the reaction of alkylnitro compounds and (V,(V-bis(trimethylsilyl)acetamide. These nitronic esters also undergo cycloaddition with alkenes to produce isoxazolidines (equation 54) (74MIP41601, 74DOK109, 78ACS(B)ll8). 

A novel one-pot synthesis of ct-nitro ketones from alkenes has been observed 01 with trimethylsilyl nitrate-chromium trioxide or a trimeihylsilyl nitrate-DMSO reagent system fEq. 2.44. ... 

In an effort to identify a more stereoselective route to dihydroagarofuran (15), trimethylsilylated alkyne 17 was utilized as a substrate for radical cyclization (Scheme 2). Treatment of 17 with a catalytic amount of AIBN and tri-n-butyltin hydride (1.25 equiv) furnishes a mixture of stereoisomeric vinyl silanes 18 (72% combined yield) along with an uncyclized reduction product (13% yield). The production of stereoisomeric vinyl silanes in this cyclization is inconsequential because both are converted to the same alkene 19 upon protodesiiyiation. Finally, a diastereoselective di-imide reduction of the double bond in 19 furnishes dihydroagaro-... 

The strict geometrical requirements for elimination can be put to further use, as illustrated by elegant procedures for the geometrical isomerization of alkenes. Trimethylsilyl potassium (10) and phenyldimethylsilyl lithium (11) both effect smooth conversion of oxiranes into alkenes, nucleophilic ring opening being followed by bond rotation and spontaneous syn fi-elimination ... 

This can also be done at room temperamre by treatment with trimethylsilyl triflate and a tertiary amine or with MesSil in the presence of hexamethyldisilazane. Enol ethers can be pyrolyzed to alkenes and aldehydes in a manner similar to that of 17-3 ... 

Finally, sulfoxides containing an a-carbonyl group and a f)-syn trimethylsilyl group [28-30], for example 1208 or 1211, are, on heating, readily converted to alkenes such as mesityl oxide 1209 and the alkyne 1212, and to trimethylsilyl phe-nylsulfenate 1210 [29, 30] (Scheme 8.11). 

Conditions for effecting conjugate addition of neutral enolate equivalents such as silyl enol ethers in the presence of Lewis acids have been developed and are called Mukaiyama-Michael reactions. Trimethylsilyl enol ethers can be caused to react with electrophilic alkenes by use of TiCl4. These reactions proceed rapidly even at -78° C.308... 

Another convenient procedure for hydrochlorination involves adding trimethylsilyl chloride to a mixture of an alkene and water. Good yields of HC1 addition products (Markovnikov orientation) are formed.3 4 These conditions presumably involve generation of HC1 by hydrolysis of the silyl chloride, but it is uncertain if the silicon plays any further role in the reaction. 

Several modifications of the Simmons-Smith procedure have been developed in which an electrophile or Lewis acid is included. Inclusion of acetyl chloride accelerates the reaction and permits the use of dibromomethane.174 Titanium tetrachloride has similar effects in the reactions of unfunctionalized alkenes.175 Reactivity can be enhanced by inclusion of a small amount of trimethylsilyl chloride.176 The Simmons-Smith reaction has also been found to be sensitive to the purity of the zinc used. Electrolytically prepared zinc is much more reactive than zinc prepared by metallurgic smelting, and this has been traced to small amounts of lead in the latter material. 

Entry 5 is an example of the use of fra-(trimethylsilyl)silane as the chain carrier. Entries 6 to 11 show additions of radicals from organomercury reagents to substituted alkenes. In general, the stereochemistry of these reactions is determined by reactant conformation and steric approach control. In Entry 9, for example, addition is from the exo face of the norbornyl ring. Entry 12 is an example of addition of an acyl radical from a selenide. These reactions are subject to competition from decarbonylation, but the relatively slow decarbonylation of aroyl radicals (see Part A, Table 11.3) favors addition in this case. 

DFT studies of the intramolecular ene-like (or the so-called 1,3-dipolar ene) reaction between nitrile oxides and alkenes show that this reaction is a three-step process involving a stepwise carbenoid addition of nitrile oxide to form a bicyclic nitroso compound, followed by a retro-ene reaction of the nitrosocyclopropane intermediate. The competitive reactions, either the intramolecular [3 + 2] cycloaddition between nitrile oxides and alkenes or the intermolecular dimerization of nitrile oxides to form furoxans, can overwhelm the intramolecular 1,3-dipolar ene reaction if the tether joining the nitrile oxide and alkene is elongated, or if substituents such as trimethylsilyl are absent (425). 

Dialkyl(trimethylsilyl)phosphines undergo 1,4-addition to a,/3-unsaturated ketones and esters to give phosphine-substituted silyl enol ethers and silyl ketene acetals, respectively. A three-component coupling reaction of a silylphosphine, activated alkenes, and aldehydes in the presence of a catalytic amount of GsF affords an aldol product (Scheme 76).290 291... 

Tris(trimethylsilyl)silane [20,21], thiols [22], germanes [23-25] and gallium hydride [26] can be added easily to terminal alkynes in the presence of Et3B/02. This process was extended to internal alkenes (Scheme 8, Eq. 8a) as well as silyl enol ethers (Eq. 8b) by using tri-2-furylgermane. In this last case, basic or acidic treatment of the main syn /J-siloxygcrmanc furnishes the corresponding E- or Z-alkene, respectively [24],... 

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