2- Trimethylsilylethylenes

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... 

Article previously published in the electronic Encyclopedia of Reagents for Orgenic Synthesis as (E)-l-Phenylsulfonyl-2-trimethylsilylethylene. DOI 10.1002/047084289X. rpll9. 

Addition Reactions. The utility of ( )-phenylsulfonyl-2-trimethylsilylethylene in the synthesis of a-substituted allylsilanes is exemplified in eq 3 for y-hydroxyvinylsilanes, and in eq 4 in the preparation of isoprenoid structures. In these reactions the reagent functions as a Michael acceptor, but a-lithiation may compete with less nucleophilic bases such as butyllithium ... 

Preparative Method bis(tri-n-butylstannyl)ethylene is treated successively with molar equivalents of n-butyllithium and chlorotrimethylsilane to give ( )-l-tri-n-butylstannyl-2-trimethylsilylethylene. ... 

For additional discussion about palladium-catalyzed coupling reactions, see also those entries dealing with organopaUa-dium complexes (e.g. tetrakis(triphenylphosphine)palladium(0), tris(dibenzylideneacetone)dipalladium-chloroform, and/or (E)-l-tri- -butylstannyl-2-trimethylsilylethylene). 

Related Reagents. (2-Bromovinyl)trimethylsilane Lithio-2-tributylstannylethylene ( )- l-Tri- -butylstannyl-2-trimethylsilylethylene. 

Radical Addition Reactions of Vinyltrimethylsilane. Reaction of the title reagent with benzenesulfonyl chloride under radical addition conditions provides ( )-l-phenylsulfonyl-2-trimethylsilylethylene (15), an acetylene equivalent in Diels-Alder reactions (eq 8). In similar fashion, thiophenol adds to vinyltrimethylsilane regioselectively.i Oxidation of the thiophe-... 

---