Triethyl phosphite → Diethyl ({5-[bis(tert-butoxycarbonyl)amino]pyridin-2-yl}methyl)phosphonate

To a solution of di-tert-butyl[6-(bromomethyl)pyridin-3-yl]imidodicarbonate (Compound 260C, 3.0 g, 7.7 mmol) in dry xylene (100 mL) was added a triethyl phosphite (6.0 g, 36 mmol). The reaction mixture was stirred at 140° C. for 4 h, then concentrated. The residue was purified by column chromatography to give the desired compound (2.5 g, yield: 92%) as a liquid. 1H NMR (CDCl3, 400 MHz): δ=1.34 (t, J=7.6 Hz, 6H), 1.39 (s, 18H), 3.43 (d, J=22.0 Hz 2H), 4.09-4.18 (m, 4H), 7.43 (dd, J=2.0, 8.0 Hz, 1H), 7.67 (s, 1H), 8.33 (d, J=8.0 Hz, 1H).