Trimethylsilylethylene

A novel route to 2-fhioromethyl- and 2-hydroxymethyl-4-alkylfurans was reported. Treating a-alkylacroleins with 1-bromo-l-trimethylsilylethylene in the presence of butyllithium yields 33. Oxidation of both double bonds followed by reaction with MsCl provides the key intermediate 34 vkdiich on treatment with TBAF produces the desired conqioimds <96TL7437>. 

Nitryl halides have been more popular reagents. Treatment of substituted styrenes with iodine and sodium nitrite leads to Markovnikov addition of NO2I (electropositive NO2) to the double bond. Elimination of HI affords (3-nitrostyrenes149150 as shown in Scheme 73.149 ( )-2-nitro-l-(trimethylsilyl)ethylene has been prepared by addition of nitryl chloride to trimethylsilylethylene, followed by elimination of HI. The author advertises the use of NO2CI and the other reagents involved as more economical than some of the other approaches to the nitroalkene (Scheme 74).151... 

Chiral Zr(q2-6-Me-pyrid-2-yl) complexes 15 react readily with terminal alkenes to give the corresponding azazirconacyclopentenes 16 in high yields. Even internal alkenes react similarly with 15b [38]. Propene and 1-hexene react with 15a so as to place the alkyl substituent in the P position, whereas styrene and trimethylsilylethylene place the Ph and Me3Si groups in the a... 

Phenylthiocyclobutanone, 422 Phenylthiolation, 456 Phcnylthiomethyllithium, 422-423 Phenylthiomethyl(trimethyl)silane, 423-424 1 -Phenylthio-1 -trimethylsilylethylene, 83 Phenylthio(triphenylstannyl)methyllithium, 424... 

A similar effect of a silyl substituent on Nazarov cyclizations has been reported in lit) annclation with 1-phenylthio-l-trimethylsilylethylene (equation II).3... 

Aldehydes Alkyidimesitylborane. Chloro-methyltrimethylsilane. Diethyl[(2-tetrahy-dropyranyloxy)methylphosphonate. N,N-Dimethylchloromethyleniminum chloride. Dimelhyl(methylthio)sulfonium tetrafluom-borate. Methoxy(phenylthio)methyllithium. Methylthiomethyl p-tolyl sulfone. 1-Phen-ylthio-1 -trimethylsilylethylene. Tetrakis-(Iriphcnylphosphine)palladium. Thexyl-chloroborane-Dimethyl sulfide. 

In contrast, bimolecular additions of allylmagnesium halides (5) to nonstrained alkenes (6) (Scheme 4 Table 1) are notoriously inefficient due to low reaction rates and the formation of regio- and stereoisomer mixtures, as well as uncontrolled consecutive reactions of the metallated addition products (7) and (8). Only trimethylsilylethylene showed a useful reactivity towards allylic Grignard reagents ... 

Hagele, G., Bdnigk, W., Dickopp, H., and Wendisch, D., Silylated phosphonic acids. Radical addition of diethyl phosphite to trimethylsilylethylene. Phosphorus Sulfur, 26, 253, 1986. 

Other substituents on the alkene are tolerated, but may influence the regiochemical outcome. The silyl group is replaced in the acylation of l-halo-2-trimethylsilylethylenes, although Lewis acids catalyzed the... 

Cycloadditions. The dienophilic properties of ( )-phenyl-sulfonyl-2-trimethylsilylethylene allow the preparation of adducts with reactive dienes such as cyclopentadiene and anthracene. The adducts are smoothly converted to alkenes upon treatment with fluoride ion, establishing the equivalence of the title reagent to acetylene. Alkylation of the a-sulfonyl carbanion can precede the elimination such that synthetic equivalents to HC CH, HC CD, and RC CH are available. The use of this reagent is highlighted by the synthesis of several functionalized dibenzobarrelenes (eq 1). The equivalency to DC CD and RC=CD is illustrated by the preparation of deuterated derivatives. 

The somewhat low reactivity of ( )-phenylsulfonyl-2-trimethylsilylethylene in Diels-Alder reactions is probably due to steric hindrance exerted by both substituents and by the poor activation imparted by the silyl group. This drawback is partially offset by the effective elimination to the alkene performed under very irdld conditions with fluoride ion. The low dienophilic reactivity of the title reagent is evident in the reaction with isodicy-clopentadiene, for which it was demonstrated that only the isomer arising from the [l,5]-hydrogen sigmatropic shift was captured by dienophiles of low reactivity. Flighly reactive dienophiles react... 

Further examples of the use of silicon to control acylations of olefins have appeared, c/s-l-Halogeno-2-trimethylsilylethylenes [prepared from frans-1,2-bis(trimethylsilyl)ethylene] are readily acylated under Friedel-Crafts conditions... 

Cycloadditions. The dienophilic properties of ( )-phenylsulfonyl-2-trimethylsilylethylene allow the preparation of adducts with reactive dienes such as cyclopentadiene and... 

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