Syntheses of Dimethyl (1S,2R)‑3-Bromocyclohexa-3,5-diene-1,2-dicarboxylate and Its Enantiomer

The title compounds, (−)-2 and (+)-2, representing potentially valuable building blocks for chemical synthesis, have each been prepared from cyclopentanone in eight steps. The pivotal one involves a resolution, through the quinine- or quinidine-promoted methanolysis of the cyclic anhydride (±)-10, leading to chromatographically separable pairs of enantiomerically pure forms of regioisomeric methyl half esters.