To a stirred suspension of Compound 1 (11 mg, 0.03 mmol) and 2-(oxetan-3-yl)ethanol (5.6 mg, 0.06 mmol) in THF (200 μL) was added triphenylphosphine (11 mg, 0.04 mmol) followed by DIAD (8 μL, 0.04 mmol). The suspension dissolved slowly upon stirring. Analysis of the reaction mixture after 2.5 h by LCMS showed the presence of starting material and so further aliquots of triphenylphosphine (5.0 mg, 0.05 mmol) and DIAD (8 μL, 0.04 mmol) were added. After stirring for 2 h, the reaction was diluted with EtOAc (10 mL), the organics washed with water (10 mL), brine (10 mL) and dried (MgSO4). The organics were concentrated in vacuo and the residue purified by automated column chromatography on silica gel (Biotage SP4, 4 g Grace Resolve cartridge) eluting with acetic acid: DCM (10% v/v, 10 CV) to remove the triphenylphosphine oxide followed by MeOH: DCM (gradient elution, 0% to 20%, 20 CV) to give Compound (4) (7.8 mg, 59%). ESI-MS m/z calculated for [M+H]+: 484.2. found: 484.2. 1H NMR (400 MHz, CDCl3) δ 8.47 (brs, 1H), 8.36 (s, 1H), 7.83-7.76 (m, 2H), 7.72 (s, 1H), 7.60 (s, 1H), 4.84-4.71 (m, 2H), 4.34 (q, J=6.0 Hz, 2H), 3.74-3.56 (m, 2H), 3.10-2.99 (m, 7H), 2.47 (s, 3H), 2.30 (ddd, J=13.6, 8.3, 5.4 Hz, 1H), 2.07-1.95 (m, 2H), 1.09-0.94 (m, 3H), 0.65-0.56 (m, 1H).
