5-(2-Methoxy-ethyl)-4-methyl-thiophene-2-sulfonic acid amide (0.082 g, 0.48 mmol) was dissolved in 2.8 mL of abs. acetonitrile and treated successively with phenyl chloroformate (0.075 g, 1.0 eq.) and triethylamine (0.167 mL, 2.5 eq.), and the mixture kept at ambient temperature for 1 h. The above prepared N-[2-(tert-butyl-dimethyl-silanyloxy)-ethyl]-4-methylsulfanyl-pyridine-2,6-diamine (0.150 g, 1.0 eq.), dissolved in a tiny amount of acetonitrile, was then added, and the mixture heated to 60° C. for 18 h. Cooling, pouring onto crashed ice, twofold extraction with AcOEt, washing with brine, drying over magnesium sulfate, and evaporation of the solvents, followed by flash chromatography (SiO2, hexane/AcOEt=1/1), yielded eventually 0.161 g of the title compound as off-white foam.
