Trimethylsilyl vinyllithium

A general route to substituted (silyl)vinylketenes has been developed and several substituted ketenes have been prepared. The synthesis of l-(l-cyclohexenyl)-2-triisopropylsilylketene is representative of this general approach (eq 6).  

Jennifer L. Loebach Rick L. Danheiser Massachusetts Institute of Technology, Cambridge, MA, USA 

Alternate Names l-lithio-l-(trunethylsilyl)ethylene a -(tri-methylsilyl)vinyllithium. 

Preparative Method prepared in situ under an inert atmosphere hy hthium-halogen exchange of (l-bromovinyl)trimethyl-silane with r-hutyllithium. 

Handling, Storage, and Precautions solutions are inflammable it is critical to preclude contact with air and moisture. 

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A fascinating reaction takes place starting with 9c (R = PhCMe2) and lithium powder in THF as the solvent. From the primarily formed 1,2-dilithioethane derivative 10c cumyllithium 12 is split off and the 2,2-bis(trimethylsilyl)vinyllithium 11 quantitatively dimerizes to yield the deep red dili-thiobutene derivative 13 ... 

SPIR0ANNELAT10N Lithium chloride-Hexamethylphosphoric triamide. N-Methyl-N-phenylaminoacetylene. (EE a(Trimethylsilyl)vinyllithium. 

When (trimethylsilyl)vinyllithiums 28 reacted with CO at 15-25 °C it gave intermediate 29, which after quenching with a chlorosilane afforded mixtures of 1 -silyloxycyclopropenes 30 and silylated allenolates 31 (Scheme 7)54. 

The a-silyl caibanions necessary to tqiply the Peterson reaction to higher substituted examples are limited by the ability to efficiently produce the anion. A clever example of an altenuitive to the Wittig reaction for ethylidene formation to give (285) with a-(trimethylsilyl)vinyllithium was utilized by Jung in the synthesis of coronafacic acid (Scheme 40). ... 

Scheme 12. Dimerization of 2,2-bis(trimethylsilyl)vinyllithium (18, R = SiMcs) and 2,2-diphenylvinylhthium (54) catalyzed by lithium metal.

Trimethylsilyl-vinyllithium 167a in THF has a half-life for the Z/E rearrangement of 0.11 sat 48 °C. Extrapolation (AH = 7.4 ( 1.5 kcal/mol) and AS = —32( 4) e.u.) to —70 °C leads to a half-life of 0.5-15 min. This is in agreement with qualitative observations in THF 1-silyl-vinyllithium species are configurationally stable only at —70 °C. The same holds for diethylether solutions. In alkane solutions in the presence of TMEDA, on the other hand, configurational lability is only observed at 25 °C. 

Vinyltrimethylsilane Metal. l-TrimethylsUylvinyl metal species are mostly used as acyl anion equivalents and as hindered vinyl anion substitutes. l-(trimethylsilyl)vinyllithium is easily accessible from (l-bromovinyl)trimethylsilane by treatment with n-butyllithium at —78°C in ether (eq 1). Other solvents and alkyllithiums can also be used for the metal-halogen exchange. The use of (l-chlorovinyl)trimethylsilane or the direct reaction of (l-bromovinyl)trimethylsilane with lithium metal are not proper methods for generating the lithium species. ... 

Realated Reagents. (2-Bromovinyl)(rimethylsilane 1-(trimethylsilyl)vinyllithium ( )-2-(trimethylsilyl)vmyUithiuin vinylmagnesium bromide. 

Preparative Methods prepared by the reaction of [E)-2-(trimethylsilyl)vinyllithium with methyl chloroformate or by carbonation of the corresponding Grignard reagent prepared from (l-bromovinyl)trimethylsilane, giving 2-trimethyl-silylacrylic acid. The methyl ester is prepared from the acid by direct esterification with absolute methanol in the presence of mineral acid, by reaction with diazomethane at low temperature, or by treatment with BF3-MeOH complex. For preparation of various trialkylsilylacrylic acid esters and f-butyl 2-trimethylsilylcrotonate, see the cited references. 

Transmetalation Reactions. Transmetalation of trimethy-lsilyl-2-trimethylstannylethylene at low temperature with n-BuLi affords ( )-2-(trimethylsilyl)vinyllithium in high yield (eq 6). ... 

The alcohol adducts from Q -(trimethylsilyl)vinyllithium and aldehydes have found many uses in organic synthesis. The ketones obtained by oxidation (eq 4) are especially good Michael acceptors and have been used in a modified Robinson annulation reaction for the construction of cyclohexenones. Cyclopropana-tion leads to cyclopropylsilane adducts, which can be converted into a variety of cyclopentenes (eq 5). Halogenation followed by stannylation gives synthons (eq 6) useful for making substituted vinylsilanes through radical reactions. ... 

Additions to Enones via the Cuprates. ( -(Trimethyl-silyl)vinyllithium undergoes Michael addition to enones, in good yields, in the presence of copper salts (eq 8). The vinyl group can be oxidized to the epoxide, which is then converted to the acyl group. The overall transformation is the addition of an acyl anion equivalent. Q -(Trimethylsilyl)vinyllithium compares favorably with other acyl anion equivalents, particularly with the vinyl ether analogs which do not add well to hindered enones. 

Diene Synthesis. a -(Trimethylsilyl)vinyllithium dimerizes in the presence of copper(I) iodide. This reaction was first observed as a side product during the formation of organo-cuprates, then developed for the synthesis of 2,3-bis(trimethyl-silyl)buta-1,3-diene (eq 9). 

Reactions with Other Electrophiles.4 a(-(Trimethylsilyl)-vinyllithium reacts with ethylene oxide to give an intermediate which has been used to set up an impressive eight-memberedring cyclization for the synthesis of (—)-laurenyne (eq 10). Here, vinyltrimethylsilane was preferred over the simple vinyl moiety because of its greater reactivity. 

Preparative Methods attempts to produce synthetically useful quantities of ( )-2-(trimethylsilyl)vinyllithium (1) by reaction of lithium metal with (2-bromovinyl)trimethylsilane (2) failed because of concomitant metalation-elimination processes involving (1) and ) However, the transmetalation process between (2) and excess f-butyllithium has been effectively used to provide (1) (eq 1). An alternative route to (1) employs the transmetalation of a l-(trimethylsilyl)-2-stannylethylene with organolithium reagents (eqs 2 and 3). ... 

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