In a mortar, 2 g of P2O5/silica gel (65% w/w) was mixed with 1,2,3,4-tetrahydroisoquinoline (10 mmol, 1.33 g) and milled for 30 s. Subsequently, 5 ml of 65% HNO3 was added slowly dropwise, and milling was continued for 20 min at room temperature until the mixture took on a deep yellow color. The progress of the reaction was monitored by TLC (n-hexane:EtOAc 70:30) to confirm the complete disappearance of 1,2,3,4-tetrahydroisoquinoline (about 30 min). After completion of the reaction, ether (50 ml) was added to the mixture and the solids were separated by filtration through a short silica gel pad and washed with ether (2 x 15 ml). The combined organic phases were washed with 10% NaHCO3 solution (20 ml) and subsequently dried with MgSO4. The solvent was removed by concentration under reduced pressure and the residue was purified by column chromatography (n-hexane:EtOAc, 2:1) to afford 7-nitro-1,2,3,4-tetrahydroisoquinoline (2b) (8 mmol, 1.4 g, 80% yield) as a yellow solid with a melting point of 121 °C. 1H NMR (δ): 8.05 (m, 2H), 7.60 (m, 1H), 3.82 (s, 2H), 3.38 (t, 2H, J = 7.4 Hz), 3.12 (t, 2H, J = 7.4 Hz), 2.83 (s, 1H).13C NMR (δ): 150.6, 145.0, 140.3, 129.6, 122.6, 121.4, 46.9, 44.1, 28.1.High-resolution mass spectra (EMS) [M+H]+ C9H10N2O2, calculated value 179.0740, measured value 179.1121.
