“…The viscous oil was mixed with a small amount of diethylether and purified by flash chromatography onto silica (eluent: diethylether). BPA2 was collected as a yellow viscous oil after evaporation of the solvent (48.2 g, isolated yield 95 %); 1 ) was added to trap residual copper and the mixture was stirred at rt for 4 h. The resin was filtered and stored to be recycled. The solvent was removed under vacuum to yield a yellowish oil M2 (59.6 g, isolated yield 93 %); 1 H NMR (400 MHz, DMSO-d 6 ) δ 4.87 (d, J = 4 Hz, 2H), 4.69 (d, J = 4 Hz, 2H), 3.56 (t, J = 6.6 Hz, 4H), 3.51 (s, 4H), 2.68 (t, J = 6.6 Hz, 4H), 2.54 (m, 4H), 2.14 (m, 4H), 1.60 (s, 6H); 13…”