[64724-28-3] · C4H7LiO · (Z)-2-Ethoxyvinyllithium · (MW 78.04)
(equivalent of the anion of acetaldehyde in aldol condensation and alkylation)
Preparative Methods: proceeds smoothly by reaction of (Z)-1-ethoxy-2-tri-n-butylstannylethylene, prepared by hydrostannation of the commercially available compound Ethoxyacetylene, with 1.1 equiv of n-Butyllithium in THF at -78 °C for 1 hr.1,2 (Z)-2-Ethoxyvinyllithium can also be prepared by halogen-metal exchange between (Z)-ethoxyvinyl bromide and butyllithium in diethyl ether at -80 °C.3
Handling, Storage, and Precautions: (Z)-ethoxyvinyllithium is stable in THF up to -45 °C, in an ethylene glycol dimethyl ether/THF mixture (1:1) up to -35 °C, and fairly stable up to -30 °C.3 (E)-2-Ethoxyvinyllithium is unstable even at -80 °C.
(Z)-2-Ethoxyvinyllithium offers a highly efficient route to a,b-unsaturated aldehydes from carbonyl compounds. Thus it reacts with aldehydes and ketones at -78 °C to produce allylic alcohols in good yields. The intermediate allylic alcohols are converted into a,b-unsaturated aldehydes under nonacidic conditions. Chromatography of the resulting allylic alcohols on silica gel or Florisil is sufficient to cause complete allylic rearrangement to the a,b-unsaturated aldehydes (eqs 1 and 2).4,5
(Z)-2-Ethoxyvinyllithium can react with the hindered ketone (1), that is unreactive with either (MeO)2POCHLiCO2Me or Ethyl Lithio(trimethylsilyl)acetate to form, after hydrolysis, an a,b-unsaturated aldehyde (eq 3).6
Addition of (Z)-1-ethoxyvinyllithium to the silyl ketone (2) and subsequent methylation provides the allenyl silyl ether (3) through C-O silyl migration and concomitant equilibration to allenyl anion (eq 4).7
(Z)-2-Ethoxyvinyllithium reacts with alkyl halides to accomplish a two-carbon chain extension of halides to aldehydes. Alkylation of (Z)-1-ethoxyvinyllithium with 1-iododecane in THF at -78 °C requires Hexamethylphosphoric Triamide as cosolvent (1 equiv) (eq 5). The allylic halide geranyl bromide is more reactive and is smoothly alkylated without HMPA as cosolvent (eq 6). The resulting enol ethers are converted by mild acid treatment (3:2:1 acetic acid-THF-water, 40 °C) to carbonyl compounds in 95% isolated yields.
Reaction of Copper(I) Iodide and Dimethyl Sulfide in THF with (Z)-1-ethoxyvinyllithium at -78 °C produces a red-brown soluble cuprate. It undergoes both conjugate addition with a,b-unsaturated carbonyl compounds (eqs 7 and 8) and direct displacement reaction with activated halides (eq 9).
(Z)-[(Trimethylsiloxy)vinyl]lithium is prepared by halogen-metal exchange between (Z)-2-bromo-1-(trimethylsiloxy)ethylene and t-Butyllithium at -70 °C in ether. Condensation of (Z)-[(trimethylsiloxy)vinyl]lithium with aldehydes and ketones occurs readily at -75 °C. Treatment of the products with dilute Hydrochloric Acid produces a,b-unsaturated aldehydes (eq 10).8
Transmetalation of the vinylstannane (4) (mixture of geometric isomers), available by treatment of 1-ethoxy-1-buten-3-yne with Tri-n-butylstannane and a catalytic amount of Azobisisobutyronitrile, with n-butyllithium in THF at -78 °C proceeds smoothly. Condensation of the resulting lithium reagent with aldehydes and ketones produces dienols which transform into dienals by either silica gel chromatography or p-Toluenesulfonic Acid in aq THF (eq 11).9
See also 1,2-Dimethoxyvinyllithium 1-Ethoxyvinyllithium 5-Lithio-2,3-dihydrofuran 6-Lithio-2,3-dihydro-4H-pyran 1-Methoxyvinyllithium
Minoru Isobe & Yoshiyasu Ichikawa
Nagoya University, Japan