8 was obtained as a white powder after flash column chromatography on a 15 g-cartridge (cyclohexane:ethyl acetate, 9:1) (182 mg, 78 % yield). The synthesis proceeded in accordance to the literature. In a 25 mL round-bottom flask copper(II) triflate (1 eq.) and 1,3-diethylurea (1 eq.) were added. Then, anhydrous THF (0.1 M) was added and the mixture was stirred to give a clear solution. Eventually, triethylamine (1 eq.) was added to give a dark solution, followed by carboxylic acid (1 eq.) addition. At last, trivinylboroxine pyridine complex (0.66 eq.) was added and the reaction was stirred overnight at 50 °C under a balloon filled with air. The solvent was evaporated under vacuum and the desired product was obtained after flash column chromatography.