Cu mediated 1,4 and 1,5 addition

1. 1,5 addition means opening of cyclopropane conjugated with a beta-ketoester.
organocupper made by organolithium works better than organocupper made by organomagnesium halide. The reason is believed that the Li can chelate with oxygen.
Cu2R made by MgR gives only 1,2 addition while Cu2R made by RLi only gives 1,5 addition.
R is 1-bromo-2-methylpropene. reaction condition: R, Li,broken glass,Et2O, 0C, then -40C, THF,HMPA,CuCN, substrate.
half eq. of CuCN is used to make the active Cu2R.

1. dummy ligand can be used to save half the bromide.