Methyl- l- trimethylsilyl allene

3-Methyl-l-(trimethylsilyl)allene (Id) is prepared by the direct silylation of the lithium derivative of l,2-butadiene. Sequential treatment of a THF solution of 1,2-butadiene with 1.0 equiv of lithium 2,2,6,6-tetramethylpiperidide (—78°C, 3 h) and 1.05 equiv of chlorotrimethylsilane (—78 °C to 25 °C, 12 h) affords (Id) in 41% yield after distillation (eq 3). 

Purification allenes (la), (lb), and (Ic) are purified by distillation at reduced pressure or by column chromatography. Allene (Id) is distilled at atmospheric pressure. The allenyl-silanes obtained by the Vermeer method typically contain up to 7-8% of the trialkylsilyl-l-butyne isomer produced by Sn2 reaction. This mixture can be used directly in most subsequent reactions without further purification. If desired, however, the alkynyl contaminant can be selectively removed by treatment of the mixture with silver(I) nitrate in (10 1) methanol-water at room temperature for one hour. 1-Methyl-l-(trimethylsilyl)-allene is obtained in 79% yield after pentane extraction and distillation. 

Handling, Storage, and Precautions 1-methyl-l-(trimethyl-silyl) allene is stable indefinitely when stored under nitrogen in the refrigerator. 

In contrast, allenylsilanes lacking a substituent at C-1 react with carbonyl compounds to produce a mixture of the desired homopropargylic alcohols and (Irimethylsilyl)vinyl chlorides. This initial product can be converted to the desired alkyne using the method of Cunico and Dexheimer exposure of the crude mixture of allenylsilane adducts to 2.5 equiv of potassium fiuoride in DMSO furnishes the homopropargylic alcohols in good yield (eq 5).  

Santelli has demonstrated that aUenylsUanes without a C-1 substituent undergo conjugate addition to Q , -unsaturated acyl cyanides to give 5,e-alkynic acyl cyanides.  

---

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... 

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

Synthesis of Five-Membered Carbocycles. 1-Substituted al-lenylsilanes react with Q ,/3-unsaturated carbonyl compounds in the presence of titanium tetrachloride to produce cyclopentenes. For example, carvone and 1-methyl-l-(trimethylsilyl)allene react smoothly to give a ds-fused bicyclic system (eq 7). ... 

---