Tris silane with alkyne

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-... 

Nickel complexes formed in situ by the reaction of NiCl.S-COD) with the iini-dazolium salts IMesHCl or IPrHCl in the presence KO Bu catalyse the hydrosilylation of internal or terminal alkynes with EtjSiH. Interestingly, Ni tri-butylphosphine complexes are inactive in this hydrosilylation reaction. The monosilylated addition products were obtained with slow addition rates of the alkyne in the reaction mixture and were formed with variable degree of stereoselectivity, depending on the type of the alkyne, the silane and the ligand on Ni [50],... 

The radical-initiated allylation of alkyl halides with allyltris(trimethylsilyl)silanes proceeds via an SH2 process mediated by a tris(trimethylsilyl)silyl radical.225 The radical-allylating agents react with alkenes, alkynes, and aldehydes via a radical chain process to give the corresponding allylsilylation products.226... 

Chatgilialoglu and Curran have found that allyltris(triniethylsilyl)silanes react with a variety of alkyl halides to provide allylation products via an Sh2 process mediated by the tris(trimethylsilyl)silyl (TTMSS) radical (Scheme 10.199) [523]. In this system the allylsilanes work as radical-allylating agents and TTMSS radical sources. We have used the reactivity of allyltris(trimefhylsilyl)silanes for allylsilyla-tion of alkenes and alkynes via a radical chain mechanism (Scheme 10.199) [524]. 

Triphenylsilyl ethers are typically prepared by the reaction of the alcohol with triphenylsilyl chloride (mp 92-94 °C) and imidazole in DMF at room temperature. The dehydrogenative silylation of alcohols can be accomplished with as little as 2 mol% of the commercial Lewis acid tris(pentaf1uorophenyl)borane and a silane such as triphenylsilane or triethylsilane [Scheme 4.98]. Primary, secondary, tertiary and phenolic hydroxyls participate whereas alkenes, alkynes, alkyl halides, nitro compounds, methyl and benzyl ethers, esters and lactones are inert under the conditions. The stability of ether functions depends on the substrate. Thus, tetrahydrofurans appear to be inert whereas epoxides undergo ring cleavage. 1,2- and 1,3-Diols can also be converted to their silylene counterparts as illustrated by the conversion 983 98.4. Hindered silanes such as tri-... 

Chatgilialoglu and co-workers (142) reported that tris(trimethylsilyl)silane reacts with terminal and internal alkynes in the presence of azoisobutyronitrile or BEt3/02 under mild conditions to give substituted vinylsilanes with high stereoselectivity. 

Hydrosilylation of Double Bonds. Tris(trimethylsilyl)silane is capable of radical hydrosilylation of dialkyl ketones, alkenes, and alkynes. Hydrosilylation of alkenes yields the anti-Markovnikov products with high regio- and good diastereos-electivity (eq 5). By using a chiral alkene, complete stereocontrol can be achieved (eq 6) The silyl group can be converted to a hydroxyl group by Tamao oxidation. 

Several new syntheses of vinylsilanes have been described. Tris(trimethyl-silyl)aluminium undergoes 5yn-addition to alkynes alternatively the same -isomers can be obtained by photochemical isomerisation of Z-1-alkenyl-silanes. Other methods described involve treatment of the lithium salts of hydrazones with trimethylsilyl chloride, Wurtz-type coupling with vinyl bromides, and reaction of acetylenes with a silyl-copper reagent followed by an electrophile. Using the hydrazone method, a route has been devised for 1,2-carbonyl transposition within ketones (Scheme 17). ... 

A major development in recent oligosilane chemistry is concerned with the tris (trimethylsilyl)silyl group in organic synthesis. One way to introduce this fragment is the use of tris(trimethylsilyl)silane as a source for silyl radicals. This way the formation of tris(trimethylsilyl)vinylsilanes is easily possible by hydrosUylating alkynes. 

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