[61288-01-5] · C12H27CuLi2 · Dilithium Tributylcuprate · (MW 248.77)
Physical Data: in ether, 1H NMR spectra have shown4 that Li2CuBu3 is not an actual species, but a more complex mixture that can be more accurately represented as a BuLi to BuCu ratio. In pentane, however, Li2CuBu3 exists in equilibrium with BuLi and LiCuBu2 (see Dilithium Trimethylcuprate).
Solubility: sol ether, THF, and pentane to -80 °C.
Preparative Method: n-Butyllithium (3.3 mmol) is added to Copper(I) Iodide (1.0 mmol) in ether at -40 °C.
Handling, Storage, and Precautions: Li2CuBu3 should be used as soon as possible following preparation. Use in a fume hood.
Li2CuBu3 behaves similarly to Li2CuMe35 in enhancing the yield and stereoselectivity in reactions with ketones (eq 1)2 (see Dilithium Trimethylcuprate). Notable in additions to hindered ketones is a depression of carbonyl reductions with Li2CuBu3 compared to the alkyllithium reagent.
Li2CuBu3 undergoes reaction with 2,3-dihydrofuran to yield 3-octen-1-ol in 75% yield.2 The optimal conditions for reaction use 5.0 equiv of butyllithium per 1.0 equiv CuI. This result raises the possibility that the reactive agent may be a cuprate species possessing a Bu:Cu ratio that is >3 (eq 2).4,6
Butylation of alkenyl-, phenyl-, and alkylmercurials with Li2CuBu3 proceeds only in moderate yield (40-60%), but nonetheless exhibits an almost tenfold enhancement in yield over that obtained with LiCuBu2.3
Timothy J. Guzi & Timothy L. Macdonald
University of Virginia, Charlottesville, VA, USA