To a mixture of (1RS,2SR,6RS,7SR)-10-oxatricyclo[5.2.1.02,6]dec-8-ene-3,5-dione (1.7 g, 0.01 mol), 4-dimethylaminopyridine (5.0 g, 0.04 mol) and 4′-chloro-4-ethylbiphen-3-yllead triacetate (9.2 g, 0.015 mol) under an atmosphere of nitrogen is added dry chloroform (50 ml)). The reaction mixture is heated at 40° C. for 5 hours, then cooled to room temperature. The mixture is diluted with ethyl acetate (50 ml), acidified with 2N aqueous hydrochloric acid (50 ml), and the mixture is filtered to remove solids. The filtrate is poured into a separating funnel and extracted with ethyl acetate. The organic extracts are combined, dried over anhydrous magnesium sulfate, filtered and the filtrate is evaporated under reduced pressure. The crude product is purified by column chromatography on silica gel to give (1RS,2SR,6RS,7SR)-4-(4′-chloro-4-ethylbiphen-3-yl)-10-oxatricyclo[5.2.1.02,6]dec-8-ene-3,5-dione.
