Trimethylsilyl allene

Solubility sol CH2CI2, benzene, most organic solvents. 

Form Supplied in colorless liquid not commercially available. Analysis of Reagent Purity IR (tf) 2955,2900,1935,1250,1210, 1055,840,800,750, and 690 cm H NMR (60 MHz, CDCI3) 50.15 (s, 9H),4.27 (d, 2H, /= 7.7),4.88 (dd, IH,7= 6.6,7.7). Preparative Method two methods have been reported for the preparation of (trimethylsilyl)allene [(TMS)allene] (1). Reductive deoxygenation of the tosylhydrazone derivative affords the title compound in 51% yield. The tosylhydrazone is readily prepared from the corresponding aldehyde, which in turn is accessed by formylation of (trimethylsilyl)ethynylmagnesium bromide with DMF (eq 1). (TMS)allene has also been prepared by flash vacuum pyrolysis of methyl (trimethylsilyl)-propargyl ether, which is obtained from silylation of methyl propargyl ether (eq 2)7 

A list of General Abbreviations appears on the front Eru apers 

Handling, Storage, and Precautions stable indefinitely when stored under nitrogen in the refrigerator. 

Propargylic Anion Equivalent. (TMS)allene reacts with electrophiles at the C-3 position in an Se2 process analogous to electrophilic substitution reactions of allyl- andpropargylsilanes. For example, upon treatment with trimethylsilyl chlorosulfonate or sulfur trioxide-1,4-dioxane, (TMS)allene yields silyl esters of sulfonic acids (eq 3). (TMS)allene undergoes conjugate addition with a, 8-unsaturated acyl cyanides to yield 5,e-acetylenic acyl cyanides.  

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Protonation of tetrakis(trimethylsilyl)allene 33 with HSO3F/ SbF5 (1 1) gives the 1,1,3,3-tetrakis(trimethylsilyl)-l-propen-2-yl cation 34. The isomeric allyl cation 35 is not formed (12, 44). 

A regioselective [3 + 2]-cycloaddition approach to substituted 5-membered carbo-cycles was made available by the use of allenylsilanes [188]. The reaction involves regioselective attack of an unsaturated ketone by (trimethylsilyl)allene at the 3-position. The resulting vinyl cation undergoes a 1,2-silyl migration. The isomeric vinyl cation is intercepted intramolecularly by the titanium enolate to produce a highly substituted (trimethylsilyl)cyclopentene derivative. 

The (trimethylsilyl)cyclopentene annulation proceeds most efficiently with the use of 1-substituted (trimethylsilyl)allenes. Even the fully methyl-substituted (tri-methylsilyl)allene reacted with both cyclic and acyclic enones to provide the corresponding cyclopentenes in good yields. 

Butynone 93 and tetrasubstituted allene 94 combine to form acetyl cyclopenta-diene 95 (Eq. 13.30) [32]. The annulation does not proceed in satisfactory yield in the case of unsubstituted trimethylsilyl allene 96 (Eq. 13.31) [32]. This is presumably due to diminished stabilization of the cationic intermediates in the case of 96, which allows competing reaction pathways to erode the yield. 

A 500-mL, three-necked, round-bottomed flask is equipped with a 25-mL pressure-equalizing dropping funnel, a mechanical stirrer, and a Claisen adapter fitted with a nitrogen inlet adapter and a low temperature thermometer (Note 1). The flask is charged with 11.5 g (0.077 mol) of (R)-(-)-carvone (Note 2), 10.8 g (0.079 mol) of 1-methyl-l-(trimethylsilyl )allene (Note 3), and 180 mL of dry dichloromethane (Note 4), and then cooled below -75°C with a dry ice-acetone bath while a solution of 17.4 g (0.092 mol) of titanium tetrachloride (Note 5) in 10 ml of dichloromethane is added dropwise over 1 hr. After 30 min, the cold bath is removed, and the reaction mixture, which appears as a red suspension, is allowed to warm to 0°C over approximately 30 min. The resulting dark red solution is poured slowly into a 2-L Erlenmeyer flask containing a magnetically-stirred mixture of 400 mL of diethyl ether and 400 mL of water (Note 6). The aqueous phase is separated and extracted with... 

Methyl-l-(trimethylsilyl]allene Silane, trimethyl(1-methyl-1, 2-propadienyl)- (10) (7A542-82-8)... 

Methyl-l-(trimethylsilyl)allene (90% purity, contaminated with 10% 1-trimethylsilyl-l-butyne) was prepared by the method of Danheiser, R. L. Tsai, Y, M. Fink, D. H. Org. Synth, 1988, 66, 1. 

A GENERAL METHOD FOR THE SYNTHESIS OF ALLENYLSILANES 1-METHYL-l-(TRIMETHYLSILYL)ALLENE... 

Formation of tetrakis(trimethylsilyl)allene by an unusual reaction from hexachlorobenzene and derivatives [120],... 

The submitters note that if pure 1-methyl-l-(trimethylsilyl)allene... 

In a similar manner, 3,3-disubstituted l,2-bis(trimethylsilyl)cyclopropenes rearrange to l,l-bis(trimethylsilyl)allenes, most likely by 1,2-silyl shift of primarily formed (1-silylvinyl)silylcarbenes. According to ab initio calculations, this reaction pathway is energetically more favorable than those including a 2,2-disilylcyclopropylidene or a 2,3-disilylpropylidene90b. 

Scheme 7-32 Allyzincation of 1 -litho-3-methoxy-3-(trimethylsilyl)allene.

The reaction of allenylsilanes with electron deficient ir-systems constitutes a powerful and general method for the tegio- and stereo-selective preparation of substituted cyclopentenes. As first reported, (trimethylsilyl)allenes function as three-carbon nucleophiles in TiCU-promoted (trimethylsilyl)cyclopen-tene annelations (Scheme 31). The annelation process involves the polarization of an a,p-unsaturated carbonyl compound by TUTU to generate an alkoxyallylic cation. Regiospecific electnqrhilic substitution of this cation at C-3 of the allenylsilane produces a silicon-stablizied vinyl cation. A 1,2-shift of the tri-... 

The first step of the mechanism involves the initial complexation of titanium tetrachloride to the carbonyl group of the electron-deficient alkene (enone) to give an alkoxy-substituted allylic carbocation. The allylic carbocation attacks the (trimethylsilyl)allene regiospecifically at C3 to generate vinyl cation I, which is stabilized by the interaction of the adjacent C-Si bond. The allylic Ji-bond is only coplanar with the C-Si bond in (trimethylsilyl)allenes, so only a C3 substitution can lead to the formation of a stabilized cation. A[1,2]-shift of the silyl group follows to afford an isomeric vinyl cation (II), which is intercepted by the titanium enolate to produce the highly substituted five-membered ring. Side products (III - V) may be formed from vinyl cation I. 

H.J. Schafer et al. achieved the formal total synthesis of the trinorguaiane sesquiterpenes ( )-clavukerin and ( )-isoclavukerin by using the Danheiser cyciopentene annulation as the key step. Racemic 4-methylcyclohept-2-en-1-one was reacted with (trimethylsilyl)allene in the presence of 1.7 equivalents of TiCU in dichloromethane at -78 °C to afford a 1 1 mixture of the c/s-fused diastereomers, which were easily separated by HPLC. The diastereomers were then converted to key fragments of earlier total syntheses of the above mentioned natural products. 

Danheiser, R. L., Carini, D. J., Kwasigroch, C. A. Scope and stereochemical course of the addition of (trimethylsilyl)allenes to ketones and aldehydes. A regiocontrolled synthesis of homopropargylic alcohols. J. Org. Chem. 1986, 51, 3870-3878. 

The use of (trimethylsilyl)allenes in a (trimethylsilyl)cyclopentene annulation was described in Section 1.6.1.2.3.1 and was shown to occur with a number of electron-deficient olefins6. The following example illustrates the extent to which stereochemistry in the olefinic acceptor can influence the course of the addition. Thus, in the addition to carvone, one diastereomeric product is obtained as a result of attack by the silylallene on the face of the double bond opposite to the isopropenyl unit. 

The most significant product is probably the pentasilyl compound, identified as o-, p-bis(trimethylsilyl)phenyltris(trimethylsilyl)allene ... 

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