Imidazole → Triphenylphosphine Oxide

Participants

Reaction Steps

Solid 1d (82 mg, 0.31 mmol), triphenylphosphine (274 mg, 1.03 mmol), and imidazole (140 mg, 2.05 mmol) are blended under argon by magnetic stirring before being dissolved in 1-methyl-2-pyrrolidinone (M-PYROL) (1.5 ml) at room temperature. Beads (1-3 mm) of iodine (261 mg, 1.03 mmol) are added over 5 min with slight heating observed. Further additions of triphenylphosphine, imidazole, and iodine (same quantities as above) are made in the order listed after 5 h, 24 h, and 56 h. More M-PYROL (0.5 ml) is added prior to the last addition. After 124 h, the reaction solution is partitioned between ethyl acetate (40 ml) and 10% sodium thiosulfate (15 ml). The aqueous layer is extracted with more ethyl acetate (3×15 ml). The combined organic layers are washed once with brine (15 ml), dried (MgSO4), and evaporated to a solid. A crop of triphenylphosphine oxide (Ph3PO) is obtained from a chilled ethyl acetate solution of this residue. More Ph3PO is removed by repeating this process with chloroform. Crude 1e is purified by preparative TLC (Analtech GF, 20×20 cm, 2,000 μ) using 9:1 CHCl3/MeOH as developing solvent. Pure 1e crystallized from 2-propanol as a white solid.

Provenance & Evidence