New synthesis of (S)-dimethyl-4,4′-dimethoxy-5,6,5′,6′-dimethenedioxy-biphenyl-2,2′-dicarboxylate by configuration transform

(R/S)-4,4′-Dimethoxy-5,6,5′,6′-dimethenedioxy-2,2′-di-(4(S)-methyl-oxazoline-1)-biphenyl has been synthesized from dimethyl-4,4′-dimethoxy-5,6,5′,6′-dimethenedioxy-biphenyl-2,2′-dicarboxylate, and then the diastereoisomer mixture was almost fully converted to a single diastereoisomer with S-configuration ((S)-3) through the key configuration transform promoted by CuI, which was confirmed by CD, HPLC and 13C NMR. The C2-symmetric biphenyl, (S)-dimethyl-4,4′-dimethoxy-5,6,5′,6′-dimethenedioxy-biphenyl-2,2′-dicarboxylate was prepared easily via the hydrolysis and ester exchange of (S)-3.