[61863-88-5] · C10H14CuLi · Lithium Bis(2-vinylcyclopropyl)cuprate · (MW 204.73)
(organometallic reagent for the introduction of a vinylcyclopropyl unit via conjugate additions to enones and ynones; useful for the construction of divinylcyclopropane and vinylcyclopropane systems as precursors to 1,3-cycloheptadiene and cyclopentenes, respectively)
Solubility: sol THF-ether (2:1) at -78 °C.
Preparative Method: prepared at -78 °C by adding a solution (THF-ether; 2:1) of 2-vinylcyclopropyllithium to 0.5 equiv of CuBr.SMe2 (see Copper(I) Bromide); the cyclopropyllithium intermediate can be generated by the metal-halogen exchange of 2-vinylcyclopropyl bromide with t-Butyllithium at -95 °C (eq 1).1
Handling, Storage, and Precautions: thermally unstable; must be generated in the absence of H2O and O2 at -78 °C; reactions with (1) and unsaturated carbonyl compounds should be carried out at -78 °C.
The major utility of lithium bis(2-vinylcyclopropyl)cuprate (1) is its reaction with a,b-alkynic esters and ketones in order to construct the divinylcyclopropane system. The 1,4-addition of (1) to the alkynic ketone (2) to produce an 8:1 mixture of the divinylcyclopropane (3) and the rearranged product (4) in 90% yield is illustrated in eq 2.2
The 1,3-cycloheptadiene product (4) is the result of the facile 3,3-sigmatropic rearrangement of the cis-(2-vinylcyclopropyl)enone isomer. In fact, the trans isomer also rearranges at higher temperatures (140-150 °C) to the same cycloheptadiene (4).
In studies directed towards the synthesis of ring-fused cycloheptadienes,2,3 an analogous cuprate containing a phenylthio ligand (see Lithium Phenylthio(2-vinylcyclopropyl)cuprate) has been added 1,4 in an addition/b-elimination process to a b-iodocyclohexenone (5) (eq 3). Subsequent rearrangement of adduct (6) leads to a ring-fused 1,3-cycloheptadiene (7).
Other variants4 of eq 3 have led to the synthesis of spirocycloheptadienes (8) (eq 4) after thermal rearrangement of the divinylcyclopropane.
2-Vinylcyclopropylcuprates also undergo rapid acylations with acid chlorides to produce 2-vinylcyclopropyl ketones such as (9) (eq 5). Ketone (9) may also be converted to a divinylcyclopropane system via its enol ether (10), and then to a spirocycloheptadiene (11) (eq 6).5
Joseph P. Marino & David P. Holub
University of Michigan, Ann Arbor, MI, USA