π-π Chelation controlled chemoselective conjugate addition of lithium dimethylcuprate

The conjugate addition of Me₂CuLi to ethyl cinnamate derivatives bearing an alkynyl group at the ortho-position, took place preferentially in the presence of the corresponding α,β-unsaturated esters bearing an alkynyl group at the distal position or having no alkynyl groups. The observed chemoselectivity is most probably a reflection of the π-π chelation between π-electrons of the olefinic moiety of the enoates and those of the C-C triple bond located at the proximal position.