6-(4-Methoxybenzyl)-8-vinylthieno[3,2-e][1,2,4]triazolo[1,5-c]pyrimidin-5(6H)-one (2.85 g; 8.42 mmol) was suspended in tetrahydrofuran (40 ml) and heated with a heat gun to effect dissolution. Similarly sodium periodate (4.14 g; 19.4 mmol) was heated in water (20 ml) to effect dissolution. The above solutions were combined with vigorous stifling. While the stirred mixture was still about 40° C., osmium(VIII) oxide (2.06 ml, 2.50% w/w, 0.21 mmol) was added and the mixture was stirred vigorously for 4 hours. The crude mixture was diluted with water (300 mL) and extracted with DCM (4×100). The organic layers were combined, dried over Na2SO4, filtered and concentrated. The crude material was purified over silica gel (120 g) eluting with 0-30% IPA in ethyl acetate over 25 minutes. Product fractions were combined and concentrated to yield the aldehyde as a brown solid (1.82 g, 63%). 1H NMR (400 MHz, DMSO-d6) δ 3.75 (s, 3H), 5.40 (s, 2H), 6.94 (d, J=8.66 Hz, 2H), 7.45 (d, J=8.53 Hz, 2H), 8.58 (d, J=4.77 Hz, 2H), 9.95 (s, 1H). LCMS (MH+, 341.2).
