[917-57-7]  · C2H3Li  · Vinyllithium  · (MW 33.99)

(introduction of vinyl groups2,3)

Physical Data: white solid; no melting point; decomposes upon heating. The 1H,4 13C,5 and 7Li NMR6 and UV-vis7 spectra of vinyllithium have all been recorded.

Solubility: sol THF, ether; slightly sol pentane, hexane;8 insol benzene.9

Analysis of Reagent Purity: determined by simple acid titration,8 by reaction with vanadium pentoxide followed by titration with standard permanganate solution,10 by hydrolysis followed by measurement of ethylene evolution,11 or by the Gilman procedure.12

Preparative Methods: prepared by a variety of methods. Direct metalation of Ethylene with Lithium metal in dimethoxymethane yields vinyllithium contaminated with lithium hydride, and other organolithio species, such as butyllithium and 1,4-dilithiobutane.13 Direct formation from ethylene can also be accomplished using Potassium t-Butoxide, n-Butyllithium, and TMEDA (N,N,N,N-Tetramethylethylenediamine) in hexane at -40 °C, followed by treatment of the vinylpotassium with Lithium Bromide.14 The lithium-halogen exchange reaction has been used, starting from vinyl chloride and lithium/sodium dispersions,10,12 or from vinyl bromide with 2 equiv of t-Butyllithium in either a Trapp solvent mixture at -120 °C15,16 or ether at -78 °C.17 This is the most convenient procedure, but lithium halide is formed during the reaction and is present as a contaminant. Halide-free vinyllithium can be prepared by transmetalation of Tetravinylstannane with phenyl- or butyllithium,8 of tetravinyllead with either lithium metal or Phenyllithium,9 or of divinylmercury with lithium dispersion in pentane.11

Purification: ether solutions can be evaporated under an inert atmosphere and the resulting solid washed with anhydrous pentane or hexane.

Handling, Storage, and Precautions: as with most alkyllithium reagents, vinyllithium reacts readily with moisture. Solid vinyllithium should be maintained at -25 °C or below, under an inert atmosphere. The solid suffers a loss in activity with time and should be used immediately upon preparation.9 Solutions of the reagent in ether or THF, under an inert atmosphere, are stable for up to 1 week at rt.8 Solid vinyllithium is violently pyrophoric, yielding a brilliant red flash on contact with air.9

Vinyl Reagents.

Vinylcuprates are easily assembled from the reaction of vinyllithium and copper species. Lithium Divinylcuprate (eq 1) has been prepared from vinyllithium using the dimethyl sulfide complex of a copper(I) halide,18 or from Copper(I) Cyanide.19 Mixed cuprates are available by the addition of vinyllithium to (2-thienyl)Cu(CN)Li,20 (MeCu)n,18 or 1-Pentynylcopper(I).21 In all the mixed cuprates the vinyl ligand is preferentially transferred.

Vinylsilanes can be prepared by reaction of a silyl halide with vinyllithium.22 Alternatively, the reaction of Bis(trimethylsilyl) Peroxide with vinyllithium yields an 80:20 mixture of Vinyltrimethylsilane and the trimethylsilyl enol ether (eq 2).23 Use of the corresponding vinyl Grignard reagent produces exclusively the enol ether.

Trialkylvinylborates can be prepared by the treatment of trialkylboranes with vinyllithium in ether at 0 °C.24 Use of a vinyl Grignard reagent to form the vinyl borate leads to lower yields in subsequent reactions. Dimesitylvinylborane is synthesized by lithium-halogen exchange of vinyllithium with fluorodimesitylborane.25 Dialkyl disulfides15 or diphenylphosphinodithioates (1)26 react with vinyllithium to produce vinyl alkyl, or aryl, sulfides in good yields (eq 3).

Ring Formation Reactions.

Vinyllithium reacts with carbonyl compounds, providing a convenient method for the introduction of a double bond for subsequent ring formation. Addition to a vinyl-substituted cyclobutanone, followed by treatment with Potassium Hydride, gives the cis- and trans-cyclooctenones in 62% yield after Cope rearrangement (eq 4).2 The vinyllithium addition yields only one diastereomer according to NMR and HPLC analysis. Similar sigmatropic reactions have been used in bicyclic systems. Vinyllithium adds to the carbonyl in bicyclo[3.2.0]heptan-6-ones (eq 5) which, when subsequently treated with potassium hydride, undergo a [1,3]-sigmatropic rearrangement of the 1-vinylcyclobutanols to yield the ring expanded product (2).27 An oxy-Cope rearrangement has been used to construct bicyclo[5.3.1]undecenones after addition of vinyllithium to bicyclo[3.1.1]heptan-6-ones.28 An intramolecular Diels-Alder reaction has been used to construct Isomer G, a component of thujopsene. The addition of vinyllithium to the acid (3) produces the precursor for the Diels-Alder cyclization (eq 6).29 Further elaboration leads to Isomer G.

Other cyclizations have also utilized vinyl groups introduced by reaction of carbonyl groups with vinyllithium, as in the base-catalyzed cyclization used in the synthesis of aphidicolin,30 the formation of substituted quinones from dimethyl squarate,31 and the cyclization using sodium in THF in the synthesis of (±)-patchoulol.32

Nucleophilic Additions.

Reaction of vinyllithium with 1-iodooctane in THF gives 1-decene in 92% yield. The use of 1,4-dibromobutane gives 1,7-octadiene in 67% yield.33 Alkenes are also available from the dimerization of vinyllithium with anhydrous Cerium(III) Chloride in THF.34 Aryl or alkyl vinyl ketones are readily formed by treating carboxylic acids with 2 equiv of vinyllithium in DME at 5-10 °C. Propionic acid produces 1-penten-3-one in 92% yield.3

Substituted enol silyl ethers are available from vinyllithium addition to silyl ketones (eq 7). Addition of the vinyllithium to the silyl ketone results in a silyloxyallyllithium which can be trapped with various electrophiles to yield the substituted enol silyl ethers.17 Vinyllithium can also be added to epoxides to give the ring-opened product,35 added to aldimines in toluene at -42 °C to produce allylamines,36 and inserted ortho to either a 2,6-di-t-butyl-4-methoxyphenyl ester substituent37 or an oxazoline group on a naphthalene ring.38

Related Reagents.

Perfluorinated vinyllithium has been prepared by transmetalation of phenyltris(perfluorovinyl)tin with 3 equiv of phenyllithium in ether at -35 to -40 °C,39 or by lithium-bromine exchange of perfluorovinyl bromide with 2 equiv of t-Butyllithium in THF at -110 °C.16 Vinylsodium is prepared by metalation of ethylene using pentylsodium with sodium isopropoxide.40 Vinylpotassium is made from vinyl chloride by metal-halogen exchange using a 90% potassium/sodium alloy.41

Related Reagents.

1,3-Butadienyl-1-lithium; Isopropenyllithium; 1-Propenyllithium; Vinylmagnesium Bromide-Methylcopper.

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Eric K. Eisenhart

Rohm and Haas Company, Spring House, PA, USA

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