Stereoselective C9 Carbon−Carbon Couplings of Quinine: Synthesis and Conformational Analysis of New <i>C</i>₂-Symmetric Dimers

An unexpected stereoselective direct dimerization occurred when 9-quinine halide was treated with butyllithium. The reaction of either (9S)- or (9R)-chloroquinine gave the same C2-symmetric dimer with 9R configuration (X-ray structure). A tentative mechanism involving radical recombination is discussed. This highly congested dimer forms two atropisomers, and their reversible interconversion was studied by NMR. Another C2-symmetric (9S)-quinine dimer connected solely by carbon−carbon bonds was obtained by the stereoselective coupling of bis(arylbromomagnesium) derivative with (9S)-chloroquinine.