[754-05-2] · C5H12Si · Vinyltrimethylsilane · (MW 100.26)
(ethylene equivalent in electrophilic substitution reactions; precursor to 3-trimethylsilyl-3-buten-2-one, a methyl vinyl ketone surrogate for Robinson annulations; homologation of aldehydes to a,b-unsaturated aldehydes)
Physical Data: bp 55-57 °C; d
Solubility: sol most common organic solvents (THF, Et2O, benzene, CH2Cl2, etc.)
Form Supplied in: commercially available from several suppliers.
Analysis of Reagent Purity: characterized by 1H, 13C, and 29Si NMR,2 and IR.3 1H NMR (500 MHz) (CDCl3): d 0.08 (9H, s), 5.67 (1H, dd, J
Purification: fractional distillation at 1 atm using an efficient Vigreux column. Some difficulty in removing trace amounts of THF (bp 67 °C) has been reported.
Handling, Storage, and Precautions: highly flammable; flash point -34 °C; hygroscopic. The reagent should be used in a well ventilated hood. Contact with the eyes and skin should be avoided.
Vinyltrimethylsilane functions as an Ethylene equivalent in electrophilic substitution reactions with sulfenyl chlorides (eq 1).6 Reaction with various arylsulfenyl chlorides provides the stable adducts (1) in high yield. Treatment of (1) with fluoride ion furnishes vinyl aryl sulfides (2) in high yield.
Vinyltriethylsilane can be elaborated in five steps to yield 3-Triethylsilyl-3-buten-2-one (4) (eq 2), a Methyl Vinyl Ketone surrogate useful in Robinson annulation reactions (eq 3).7 The analogous annulation reaction using methyl vinyl ketone gives poor yields.
Vinylsilanes react with Chlorosulfonyl Isocyanate without the aid of Lewis acid catalysts to form b-lactams, e.g. (5), which subsequently undergo hydrolysis to the corresponding trans-a,b-unsaturated primary amides, e.g. (6) (eq 4).8
Vinyltrimethylsilane undergoes [3 + 2] cycloaddition reactions with the aldehyde-derived nitrone (7) to provide the corresponding (trimethylsilyl)isoxazolidine adduct (8) in 84% yield (eq 5).9 Treatment of (8) with aqueous HF furnishes the a,b-unsaturated aldehyde (9) in 95% yield. This methodology is general for the homologation of aldehydes and serves as an alternative to the traditional Wittig-type alkenations.
The title reagent serves as an ethylene equivalent in aliphatic Friedel-Crafts acylation reactions involving cyclic a,b-unsaturated acid chlorides. For example, the acid chloride (10) reacts with vinyltrimethylsilane in the presence of Tin(IV) Chloride to give the divinyl ketone intermediate (11), which then undergoes a Nazarov cyclization, thus producing the bicyclopentenone (12) in 46% overall yield (eq 6).6,10
Vinyltrimethylsilane serves as a useful precursor to 1-chlorocyclopropene (14).13 Reaction of the vinylsilane with Phenyl(trichloromethyl)mercury12 in refluxing benzene followed by fluoride-induced elimination of TMSCl from the cyclopropane (13) furnishes 1-chlorocyclopropene in good yield, as evidenced in the subsequent Diels-Alder reaction with 1,3-diphenylisobenzylfuran (eq 7). A previous synthesis13 of 1-chlorocyclopropene gave only 5-10% yield.
Reaction of the title reagent with Benzenesulfonyl Chloride under radical addition conditions14 provides (E)-1-Phenylsulfonyl-2-trimethylsilylethylene (15),15 an Acetylene equivalent in Diels-Alder reactions (eq 8). In similar fashion, Thiophenol adds to vinyltrimethylsilane regioselectively.16 Oxidation of the thiophenol adduct provides the sulfone (16) (eq 9), which serves as a latent exomethylene unit in the enantioselective synthesis of (1R)-[(methylenecyclopropyl)acetyl]-CoA (17).17 The sulfone (16) is also used in the high yield preparation of allylsilanes, vinyl sulfones, and 2-(benzenesulfonyl)allyl alcohol derivatives.18
Reaction of vinyltrimethylsilane with the nonstabilized 2-azaallyl anion (19), generated in situ from the (2-azaallyl)stannane (18) (eq 10), produces, after quenching with MeI, the pyrrolidine (20) as a single diastereomer in 77% yield (eq 11).21 Some evidence suggests that the cycloaddition is stepwise and that the
W-conformation of the anion predominates in the cycloaddition sequence.
Vinyltrimethylsilane undergoes highly regioselective hydroesterification reactions to furnish either ethyl 3-(trimethylsilyl)propionate (21) or ethyl 2-(trimethylsilyl)propionate (22), depending on the choice of catalyst and reaction conditions (eq 12).20 Highly regioselective (>96% b-selective) hydroformylations of vinylsilanes containing bulky alkyl and aryl substitutents on silicon have been achieved using Carbonylhydridotris(triphenylphosphine)rhodium(I) as catalyst.21
Glenn J. Fegley
Indiana University, Bloomington, IN, USA