Reaction Steps
A sample of 15a (38.7 mg, 0.048 mmol) was dissolved in trimethylphosphite (5.0 mL). The solution was refluxed under argon for 1.5 days. The P(OMe)3 was evaporated at reduced pressure. The residue was chromatographed (silica, CH2Cl2/MeOH, 0→5%) to yield a dark purple solid (24.6 mg, 65%): 1H NMR δ 1.64 (s, 9H), 3.15 (m, 2H), 3.32-3.36 (m, 2H), 3.43 (s, 3H), 3.47 (s, 6H), 3.50 (s, 3H), 3.81-3.87 (m, 4H), 4.84 (s, 2H), 5.44 (m, 1H), 7.35 (d, J=8.1 Hz, 2H), 8.17 (d, J=8.1 Hz, 2H), 9.10 (s, 2H), 9.40 (s, 2H), 9.50-9.51 (m, 1H), 9.73-9.74 (m, 2H), 10.30-10.31 (m, 2H); LD-MS obsd 803.7, calcd 800.3104 (C41H48N4O9P2); λabs (log ε) 407 (4.90), 504 nm; λem(λexc 407 nm) 636 nm, 702 nm. Varying amounts of a less polar purple solid (16a-Br) were isolated along with small amounts of the starting material 15a (limited characterization). Data for 16a-Br: 1H NMR δ 0.86-0.95 (m, 1H), 1.65 (s, 9H), 1.91-2.00 (m, 1H), 3.13-3.40 (m, 6H), 3.44 (s, 3H), 3.48 (s, 3H), 3.55-3.85 (m, 2H), 4.83 (s, 2H), 5.51-5.61 (m, 1H), 7.34 (d, J=8.1 Hz, 2H), 8.17 (d, J=8.1 Hz, 2H), 9.08-9.10 (m, 2H), 9.37-9.41 (m, 2H), 9.49-9.51 (m, 2H), 9.67-9.68 (m, 1H), 9.84-9.85 (m, 1H), 10.30 (s, 2H); LD-MS obsd 773.6, calcd 773.2 [(M+H)+, M=C39H42BrN4O6P2]; λabs 407, 502 nm; λem (λexc 407 nm) 634, 702 nm.
