1-Trimethylsilyl-l-alkynes

In an analogous reaction, 1-trimethylsilyl-l-alkynes have been synthesized in good to excellent yield on treatment with trimethylsilyl chloride, catalytic amounts of silver salts, and DBU in refluxing dichloromethane (Scheme 1.61).135... 

Perhaps the most widely reported use of silver acetylides is in the deprotection of 1-trimethylsilyl-l-alkynes. Schmidt and Arens first reported the treatment of 1-trimethylsilyl-l-alkynes with silver nitrate to give the silver acetylide in situ, which, when treated with potassium cyanide, is converted to the free alkyne (Scheme 1.63).137 This very mild and selective, but toxic, means for the selective... 

Pale and coworkers provided the first example of combined desilylation/coupling catalytic for silver. They found that 1-trimethylsilyl-l-alkynes in the presence of tetrakis(triphenylphosphine)palladium, a silver(I) salt, and an activator (potassium carbonate in methanol, or TBAF-3H20) in DMF coupled with vinyl triflates and aryl iodides to give enynes good yields (Scheme 1.66).143,144 Although silver salt was not necessary for reaction when TBAF-3H20 was used for activation of the carbon-silicon bond, a small to significant improvement was observed for all reported... 

Under similar conditions, but with the addition of chlorides, Nagasaka et al. were able to directly engage 1-trimethylsilyl-l-alkynes in coupling reactions with aryl... 

To a suspension of iodosylbenzene (1.1 g, 5 mmol) and the appropriate 1-trimethylsilyl-l-alkyne (5 mmol, prepared from 1-alkyne and trimethylchlorosilane in nearly quantitative yield, or obtained commercially) in chloroform (10 ml) was slowly added boron trifluoride etherate (710 mg, 5 mmol) at 0°C. The mixture was stirred at room temperature for 3-4 h, then recooled at 0°C and a solution of p-toluenesulphonic acid hydrate (3.8 g, 20 mmol) in water (20 ml) was added the resulting mixture was stirred vigorously for a few minutes. The organic phase was separated and the aqueous phase was washed with additional chloroform. The combined organic phase was washed with water, dried and concentrated. The residual oil solidified upon addition of ether. The solid was filtered, washed with ether and air-dried to give alkynyl phenyliodonium tosylates (62-89%). 

Hydromagnesiation vinylsilanes.2 The hydromagnesiation (10, 130-131) of 1-trimethylsilyl-l-alkynes with isobutylmagnesium bromide followed by alkylation affords (Z)-l,2-dialkylvinylsilanes in high yield. 

Hydroboration of 1-trimethylsilyl-l-alkynes with BH3 SMe2 in a 3 1 ratio, followed by oxidation of the resultant trivinylborane with anhydrous trimethylamine oxide, provides an operationally simple, one-pot synthesis of alkyl-substituted acylsilanes in good yield from readily available starting materials. ... 

Diastereomerically enriched P-hydroxy silanes are also accessible from a,P-epoxy silanes and reaction of these with organocuprate reagents. The epoxy silanes are synthesized by epoxidation of (E)- or (Z)-vinylsilanes with m-chloroperbenzoic acid. The required (Z)- and ( )-vinylsilanes can be obtained by hydroboration-protonolysis of 1-trimethylsilyl-l-alkynes or by hydrosilylation of 1-alkynes, respectively. 

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... 

Methylenetetrahydropyrans could also be obtained by [CpRu(CH3CN)3]PF6-catalyzed coupling of allylethylether with optically active 1-trimethylsilyl-l-alkyn-3-ols followed by in situ ketalization. Fiuther Fewis acid-induced cyclization afforded enantiomerically pure 1,5-oxygen-bridged carbocycles [62]. 

Because the type 1 monomers do not give rise to high-molecular-weight polymers, we next considered 3-(trimethylsilyl)-l-alkynes (2) as monomers 12). 

The high regioselectivity in the formation of a-allenic alcohols from boron reagents at low temperature is markedly different from that seen with the titanium reagent derived from 1-trimethylsilyl-l-bu-tyne, in which exclusive formation of 3-alkynic alcohols is observed. This result was explained by a rapid exchange between the allenic and alkynic structures, as shown in equation (2). The alkynic structure is thermodynamically less stable and kinetically more reactive than that of the allenic form. At lower temperature, the rate of equilibrum becomes faster than the subsequent reaction with aldehydes and thus the alkynic species becomes the major reaction form. 

Many monomers with simple structures, including phenylacetylene, t-butyl-acetylene, 1-phenyl-1-propyne, 2-octyne, and 1-trimethylsilyl-l-propyne, are commercially available. These monomers are usually purified by distillation in the presence of suitable drying agents prior to use. On the other hand, monomers that are more complex, such as ort/zo-substituted phenylacetylenes, A-pro-pargylcarbamates, ring-substituted diphenylacetylenes, and 1-chloro-l-alkynes, must be synthesized. Derivatization of simple alkynes rather than formation of the acetylenic moiety, is frequently applied to synthesize such monomers. These are then purified by vacuum distillation or column chromatography. 

The reaction of 1-21 with alkynes is regioselective. When unsymmetrical alkynes such as 1-phenyl-1-butyne was used, l-43a and l-44a both as single regioisomers were isolated upon hydrolysis of reaction mixture at 50 °C and 90 °C respectively. The Ph group was selectively located at a-position of CpaZr moiety. The substituents on alkynes also have an effect on the chemoselectivity of the reaction. When 1-trimethylsilyl-l-propyne was used, only zirconacyclopentadiene l-43b was isolated regioselectively, and the corresponding zirconacyclohexadiene complex was not isolated (Scheme 1.21) [47, 48]. 

Titanacyclopentenes are formed from the reaction of Cp2TiEt2 and alkynes as described above (Eq.20) [18]. However,interestingly,when a silylated acetylene such as 1-trimethylsilyl-l-propyne was used, l-methyl-l-(trimethylsi-lyl)methyl cyclopropane, other than the expected titanacyclopentene, was formed (Eq. 33) [18]. This reaction chemistry is different from that of analogous zirconocene. Formation of a titanocene-carbene complex is proposed via Michael addition-type reaction in the titanacyclopentene intermediates. 

An exceptional approach to phosphorus-substituted alkoxyallenes via isomerization of alkynes was introduced by Beletskaya s group. The treatment of 1-alkoxy-l-propynes 23 with l-halo-2,2-bis(trimethylsilyl)phosphaethen 24 furnished alkoxyallenes 25 (Scheme 8.9) [31]. 

An HfCl4-catalyzed carbosilylation of phenylacetylene with 3-(trimethylsilyl)-l,2-butadiene giving the 1,3,4-pentatrienylsilane 61 was also reported [32]. In this reaction, 3-(trimethylsilyl)-l,2-butadiene may be converted by HfCl4 to 2-butynyltri-methylsilane, which reacted further with an alkyne to afford the vinylic allene 61. 

Rhodium-catalyzed silylformylation proceeds smoothly in branched 1-alkynes at 25 °C as shown in Table 3. The stereochemistry at the chiral carbon involved in alkynes is retained intact under the silylformylation conditions. (A)-28, (rhodium particles co-condensed with mesitylene. 3-Trimethylsilyl-l-propyne 40 reacts similarly to give 41 (Equation (7)). " / //-Butylacetylene does not work as a substrate for the silylformylation because of the bulky tert-huty group on the i/>-carbon. In contrast to /< r/-butylacetylene, trimethylsilylacetylene 42 gives 43 in a fair yield (Equation (8)). ... 

Saccharin pseudochloride 112 (R = C1) reacts with 1-diethylamino-l-propyne to give 113. When the corresponding 3-ethoxy derivative 112 (R = OEt) was treated with the same alkyne, a ring-expansion product 114 (R = OEt) was isolated. On the other hand, the analogous thiazepine 114 (R = OSiMc3) is obtained, together with the ketone derived by hydrolysis of the silyl enol ether, by the reaction of saccharin with BuLi/trimethylsilyl chloride (TMCS)... 

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