[123206-02-0] · C8H14CuLiO2 · Lithium Bis(1-ethoxyvinyl)cuprate · (MW 212.71)
Physical Data: homogenous, red solution displaying some temperature sensitivity; dec. estimated between -35 and -25 °C.3
Solubility: sol THF.
Preparative Methods: prepared under an inert atmosphere of argon by the rapid addition of 2 equiv of 1-Ethoxyvinyllithium5 in THF at -78 °C to a suspension of purified Copper(I) Iodide at -78 °C, which is stirred at -30 °C for 1 h to afford a deep red solution.3
Handling, Storage, and Precautions: air- and moisture-sensitive reagent prepared in situ. Use in a fume hood.
Lithium bis(1-ethoxyvinyl)cuprate affords transfer of the 1-ethoxyvinyl ligand, an acyl anion equivalent,6 via conjugate addition to a,b-alkenyl ketones7 (25-91% yield)3 (eqs 1 and 2). This reaction is sensitive to steric hindrance resulting from substitution in the a,b-enone, especially at the b-position, resulting in slow 1,4-addition. Use of excess reagent can sometimes overcome this limitation. The n-propynyl mixed cuprate reagent can be used effectively to give conjugate transfer of the 1-ethoxyvinyl ligand to 2-cyclohexen-1-one (83% yield).3
Employment of Boron Trifluoride Etherate in conjunction with lithium bis(1-ethoxyvinyl)cuprate gives an enhancement of reagent efficiency as well as improved control over the regioselectivity in the reaction, preventing 1,2-addition (eq 3).8
A lithium bis(1-ethoxyvinyl)cyanocuprate reagent can be prepared by the transmetalation of the vinylstannane with lithium dimethylcyanocuprate to give effective conjugate addition of the 1-ethoxyvinyl ligand to an a,b-enone.9 The resulting vinyl ether 1,4-adducts can be readily hydrolyzed under mildly acidic conditions (0.1 N HCl/ether, 0.1 N oxalic acid/MeOH, or SiO2 in wet benzene) to afford 1,4-diketones in 57-95% yield.3
Chemoselective 1,2-addition of lithium bis(1-ethoxyvinyl)cuprate to an aldehyde can be achieved in moderate yield (eq 4).4
Coupling of lithium bis(1-ethoxyvinyl)cuprate with allylic bromides occurs in good yield (eq 5).3,10 However, this reagent fails to give desired coupling products with saturated primary and secondary alkyl bromides, affording cuprate reagent self-coupling products; attempted opening of oxiranes was also unsuccessful.3
Christopher W. Alexander
Emory University, Atlanta, GA, USA
Robert K. Boeckman, Jr.
University of Rochester, NY, USA