Trimethylsilyl-1,3-butadiene

Labrecque, D., Tetrahedron Lett. 1992, 33, 7997. Similar results are obtained with boronate complexes see Tsai, D. J. S. Matteson, D. S., Organometallics 1983, 2, 236. 

Denis Labrecque Tak-Hang Chan McGill University, Montreal, Montreal, Quebec, Canada 

Physical Data bp 110-115 °C, 70-74 °C/210 irunHg. Solubility freely sol all organic solvents. 

Handling, Storage, and Precautions reasonably stable in the absence of air and radical initiators. It should be kept in a stoppered flask or sealed ampule in the presence of hydroquinone. Its toxicity is unknown, but the presence of a trimethylsilyl group is generally benign. 

Diels-Alder Reactions. ( )-I-Trimethylsilyl-1,3-butadiene undergoes Diels-Alder reactions with the usual dienophiles, with unimpaired endo stereoselectivity, but at a somewhat slower rate than 1,3-butadiene itself (eq 1). The regioselectivity with un-symmetrical dienophiles is poor (eq 2). The adducts are allylsilanes, which react with electrophiles in the usual way (eqs 3 and 4) to give cyclohexenes with a double bond shifted from the original position.  

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Reaction with Sulfur Compounds. In a similar coupling reaction to those of alkyl halides, (1) reacts in the presence of a nickel catalyst with allylic dithioacetals to yield l-(trimethylsilyl) butadienes (eq 8). ... 

Allylic and Propargylic Alcohols. Allyl silanes (22), formed as Diels-Alder adducts from 1-trimethylsilyl butadiene, can be converted regiospecifically into allylic alcohols (Scheme 8), either with allylic rearrangement, using peracids, or without rearrangement. The latter transformation is achieved by first reacting the allyl... 

The formation of 2-(t-butyl)-2-trimethylsilyl-2//-thiopyran has recently been reported from 1-substituted 1,3-butadienes with /-BuCSSiMe3 (92MI1) (see Scheme 2). An unusual product with proposed structure 47b has been reported (84JOC5143) from benzothiopyrone 46 on reaction with sec-butyl lithium (46 - 47a — 47b, Scheme 3) on the basis of spectroscopic data. 6-Methylthio-2//-thiopyran was isolated after the flash vacuum thermolysis of more complex starting precursors (93TL2605). 

The silicon- and sulfur-substituted 9-allyl-9-borabicyclo[3.3.1]nonane 2 is similarly prepared via the hydroboration of l-phenylthio-l-trimethylsilyl-l,2-propadiene with 9-borabicy-clo[3.3.1]nonane36. The stereochemistry indicated for the allylborane is most likely the result of thermodynamic control, since this reagent should be unstable with respect to reversible 1,3-borotropic shifts. Products of the reactions of 2 and aldehydes are easily converted inlo 2-phenylthio-l,3-butadienes via acid- or base-catalyzed Peterson eliminations. 

A similar elimination in which the tin is attacked by fluoride anions (cf. the reaction of silanes with F ) has been used179 to synthesize terminal methylene compounds as in equation (75). An analogous reaction sequence using a trimethylsilyl group in place of the trialkyltin group has been published by Hsiao and Shechter180 as part of a synthesis of substituted 1,3-butadienes. 

In 1995, these authors applied this methodology to the first total synthesis of the biosynthetically and unusual marine natural products, gracilins B and Thus, the key step of this synthesis was the enantioselective Diels-Alder reaction of 2-((trimethylsilyl)methyl)-butadiene with A-(2-iert-butylphenyl)maleimide in... 

A carbon-iron bond is also formed by the reaction of the cyclopropenium salt 185 with dicarbonyl(i/5-cyclopentadienyl)(trimethylsilyl)iron [92], (Scheme 69) In the reaction with benzocyclobutenylidene- 5-cyclopentadienyliron(II) hexafluorophosphate 186, CpFe(CO)2R (R=cyelo-C3H5, CH2-cyclo-C3H5) is converted to the allene and butadiene complexes, 187 and 188, respectively [93]. (Scheme 70)... 

Corriu et al. have reported that the coupling reaction of 2-(iV,iV-dimethylaminomethyl)phenyllithium with (McvSi)vSiCI 53 affords 2-(iV,iV-dimethylaminomethyl)-l-[tris(trimethylsilyl)silyl]benzene 894. No evidence has been found that the intramolecular iV-ligand coordinates to the silicon atom of 894. Upon UV irradiation, the trisilane forms a transient silyene 895, which has been trapped with 2,3-dimethyl-2,3-butadiene and triethylsilane to give the oligosilanes 896 and 897 as well as 898-900, (Scheme 126).859 Apparently, the bulk on the two ligands is insufficient to provide kinetic stabilization of the silylene intermediate 895. 

The Pd-catalyzed reaction was applied to the synthesis of (allenylmethyl) silane derivatives [98], A series of 4-substituted-l-trimethylsilyl-2,3-butadienes 110 were prepared in 64—91% yields from easily accessible (3-bromopenta-2,4-dienyl)trimethylsi-lane 109 and soft nucleophiles 102 in the presence of 2 mol% of a Pd catalyst generated in situ from [PdCl(jT-aHyl)2]2 and dpbp (Scheme 3.55). 

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. 

Reactions of 3-methylthio-4-trimethylsilyl-l,2-butadiene with electron-poor monosub-stituted and disubstituted alkenes were promoted by a catalytic amount of ethylaluminum dichloride, affording the corresponding methylenecyclobutanes with high selectivities and with yields ranging from 37% for methyl crotonate to 97% for methacrylonitrile15. 

Electron-rich 3-methoxy-4-trimethylsilyl-l,2-butadiene (22) reacted with several electron-poor alkenes in the presence of diethylaluminum chloride to afford methylene cyclobutanes 23. Reactions with alkynes were performed in the presence of methylalu-minum bis(2,4,6-tri-t-butylphenoxide) (equation 7)16. 

An outstandingly reactive diene is l-methoxy-3-(trimethylsilyloxy)-l,3-butadiene ( Danishefsky s diene ) 4, prepared by the action of trimethylsilyl chloride on the ketone 3 in the presence of zinc chloride/triethylamine (equation 7)6. The reaction of diethyl mesoxalate with Danishefsky s diene gives the dihydropyran 5 with the (trimethylsily-loxy)dienes 6 and 7, mixtures of dihydropyrans are obtained, in which the meta-isomers predominate (equations 8 and 9)7. 

A convenient procedure for the synthesis of tellurophene employs the reaction of Na2Te with l,4-bis(trimethylsilyl)-l,3-butadiene. The crude product is isolated as the corresponding dibromide, which is then reduced to tellurophene. ... 

Tellurophene. A mixture of tellurium (4.0 g, 31 mmol), sodium formaldehyde sulphoxylate of 85% (28 g, 200 mmol), sodium hydroxide (17 g, 425 mmol) in 150 mL water is heated at reflux, under N2 atmosphere for 15 min, and then cooled at 20°C. A solution of 1,4-bis(trimethylsilyl)-l,3-butadiene (8.2 g, 42 mmol) in 100 mL of ethanol is slowly added to the stirred sodium telluride solution, the mixture is heated at reflux for 15 min, then stirred at 20°C for 3 h and extracted with ether. The extract is dried (Na2S04), filtered, and 10 mL (200 mmol) of bromine are added dropwise until the bromine colour persists. This solution is concentrated in a water bath under aspiration vacuum to a volume of 50 mL, and the red precipitate of tellurophene dibromide is collected 8.9 g (84%), m.p. 120°C dec. 

The THF adduct of dilithio-l,4-bis(trimethylsilyl)-2-butene (14) (Figure 6), which was prepared by the same method as the compounds of type 13 (a reduction of the corresponding 1,3-butadiene with metallic lithium, as described in Section II. E, can be an... 

Simple dienes react readily with good dienophiles in Diels-Alder reactions. Functionalized dienes are also important in organic synthesis. One example which illustrates the versatility of such reagents is l-methoxy-3-trimethylsilyloxy-1,3-butadiene (.Danishefsky s diene) 1 Its Diels-Alder adducts are trimethylsilyl enol ethers which can be readily hydrolyzed to ketones. The /j-mcthoxy group is often eliminated during hydrolysis. 

Verschiedene 1-Metall- und 1-Bor-Derivate von l-Trimethylsilyl-l,2-butadien, insbeson-dere Triisopropyloxy-(l-trimethylsilyl-l,2-butadienyl)-titan, reagieren mit N-Alkyl-aldiminen aliphatischer Aldehyde praktisch ausschliefllich unter Bildung von (nach Hydrolyse) fftreo-4-Alkylamino-3-methyl-l-trimethylsilyl-l-alkinen in meist hohen Ausbeuten3, wie nachstehend fur die Synthese von 4-Benzylamino-3-methyl-l-trimethyl-silyl-l-heptin formuliert. 

Heteroatoni groups such as boron or silicon can activate or direct synthetic reactions. Use of such activation has become of major importance in organic syntheses. Examples in this volume are BORANES IN FUNCTIONALIZATION OF DIENES TO CYCLIC KETONES BICYCLO[3.3.1]NONAN-9-ONE and BORANES IN FUNCTIONALIZATION OF OLEFINS TO AMINES 3-PINANAMINE. Use of trimethylsilyl or trimethyl-silyloxy groups to activate a 2-butenone or a butadiene are illustrated by the preparations 3-TRIMETHYLSILYL-3-BUTEN-... 

The unsubstituted spirononadiene has been obtained from silicon atoms and the diene, albeit in low yield. However it results in better yield from methoxytris(trimethylsilyl)silane and the diene on photolysis. a-Elimination is non-specific but favours the methoxysilylene, addition giving the two silacyclopentenes (111) and (112) with buta-1,3-diene (Scheme 186). Pyrolysis with excess butadiene gives the spiro derivative, in support of the cyclosilylene intermediate (113 Scheme 187) (81JA7344). 

Diels-Alder reactions of bis(trimethylsilyl)acetylene.1 A catalyst obtained from TiCl4 and (C2H5)2A1C1 (1 20) effects Diels-Alder reactions of this acetylene with butadiene and methyl-substituted derivatives to form l,2-bis(trimethylsilyl)-cyclohexa- 1,4-dienes in 70-78% yield (equation I). The yield is low (15%) only when R, R4 = CH3,R2,R3 = H because of polymerization of the diene. The products undergo thermal dehydrogenation at 240° to form l,2-bis(trimethylsilyl)ben-zenes in almost quantitative yield. This cycloaddition has been effected in low yield with an iron-based catalyst. 

Lithium butyldimethylzincate, 221 Lithium sec-butyldimethylzincate, 221 Organolithium reagents, 94 Organotitanium reagents, 213 Palladium(II) chloride, 234 Titanium(III) chloride-Diisobutylalu-minum hydride, 303 Tributyltin chloride, 315 Tributyl(trimethylsilyl)tin, 212 3-Trimethylsilyl-l, 2-butadiene, 305 Zinc-copper couple, 348 Intramolecular conjugate additions Alkylaluminum halides, 5 Potassium t-butoxide, 252 Tetrabutylammonium fluoride, 11 Titanium(IV) chloride, 304 Zirconium(IV) propoxide, 352 Miscellaneous reactions 2-(Phenylseleno)acrylonitrile, 244 9-(Phenylseleno)-9-borabicyclo[3.3.1]-nonane, 245 Quina alkaloids, 264 Tributyltin hydride, 316 Conjugate reduction (see Reduction reactions)... 

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