“…Activation of unlabelled 7, i.e., u-7, with 3-nitro-1H-l,2,4-triazole and diphenyl phosphorochloridate, a method that was so efficient for the corresponding activation of thymine derivatives [6] [ 151, merely resulted in the formation of (2',3',5'-tri-O-benzoyluridin-04-yl) 3-nitro-lH-1,2,4-triazolyl phenyl phosphate (30% yield), a dead-end product with respect to further substitutions at 04. In contrast, the relatively stable crystalline key intermediate u-8a/b was obtained from u-7 in 94% yield using phosphoryltris(lH-l,2,4-triazole) as activator [16].…”