[24743-97-3] · C16H33CuLiP · Lithium Divinylcuprate-Tributylphosphine · (MW 326.95)
Physical Data: see entries for Lithium Divinylcuprate, Tri-n-butylphosphine.
Solubility: sol ether, THF.
Analysis of Reagent Purity: an assay to determine relative thermal stabilities4 can be used to estimate reagent quality and concentration: a sample of known volume and temperature is quenched with excess PhCOCl. The yield of phenyl vinyl ketone is measured by GC, the response of which is calibrated using authentic product and n-dodecane as internal standard.
Preparative Methods: a round-bottom flask equipped with magnetic stirring bar and rubber septum is charged with Copper(I) Iodide-Tributylphosphine.5-7 Under a nitrogen atmosphere, THF is added and the flask cooled to -78 °C; to the resultant cold solution is slowly added 2.0 equiv of Vinyllithium8 in THF. A blue-black mixture forms, which can be used immediately. Alternate preparations, by addition of 1.0 equiv of n-Bu3P to a THF slurry of CuI before addition of 2 equiv of vinyllithium, or by use of CuBr(n-Bu3P)2,9 may be possible.
Handling, Storage, and Precautions: best results are obtained with high purity CuI salts,10 dry, O2-free solvents, and alkyllithium solutions free of contaminating alkoxides or hydroxides.11 Like most alkyllithium reagents, vinyllithium is pyrophoric;12 care must be exercised in its handling. Homocuprates are stabilized in the presence of stoichiometric quantities of n-Bu3P; there is no noticeable decomposition at -78 °C.6 Use in a fume hood.
Phosphine-ligated homocuprates were introduced early in the development of organocopper chemistry.6,13 The n-Bu3P ligand solubilizes the homocuprate in ether solvents, increasing its reactivity, and also retards thermal decomposition. Generally, the presence of stoichiometric quantities of the ligand make reaction workup unsatisfactory;6,13a,14 for this reason, various heterocuprates15 have found wider application in organic chemistry.
Lithium divinylcuprate-tributylphosphine undergoes efficient substitution reactions with primary iodoalkanes when used in excess.6 It is more commonly found as a reagent in 1,4-additions to 2-alkenones, and has found application in the stereocontrolled synthesis of 1,3,5-triols16 and 11-substituted 11-deoxyprostaglandins.17 A typical example is the 1,4-addition to isophorone (eq 1);5 the thermal stability of the reagent allows normally sluggish 3,3-disubstituted 2-alkenones to be used as substrates. The isolated chemical yield (60%), when compared to GC analysis of the crude product (85%), is indicative of the difficulty that can be encountered in efficiently separating the phosphine from the product.
Creighton University, Omaha, NE, USA