Add copper(II)sulfate pentahydrate (0.026 g; 0.2 equiv; 0.106 mmoles) and L-ascorbic acid sodium salt (0.21 g; 2.0 equiv; 1.06 mmoles) to a deoxygenated solution of tert-butyl N-but-3-ynyl-N-[2-[2-(indan-2-ylamino)-7,8-dihydro-5H-pyrido[4,3-d]pyrimidin-6-yl]-2-oxo-ethyl]carbamate (0.252 g; 1.0 equiv; 0.53 mmoles) in dimethylformamide (6 mL) and water (3 mL) (including toluene (0.05 mL) as an internal standard). Heat the reaction vessel to 90° C. and then add azidotrimethylsilane (0.565 mL; 8 equiv; 4.24 mmoles) slowly. Stir at 90° C. for 4 hours, then dilute the reaction mixture with water (100 mL) and ethyl acetate (50 mL), and extract 3×50 mL ethyl acetate. Wash the combined organic extracts with brine, dry over magnesium sulfate, filter, and concentrate. Purify the crude product by column chromatography (0 to 10% methanol in ethyl acetate) to give tert-butyl {2-[2-(2,3-dihydro-1H-inden-2-ylamino)-7,8-dihydropyrido[4,3-d]pyrimidin-6(5H)-yl]-2-oxoethyl}[2-(1H-1,2,3-triazol-4-yl)-ethyl]carbamate (0.174 g; 63%) as a colorless foam: MS (m/z): 519 (M+1).
