p-Toluenesulfonic acid → (S,Z)-3-[(5-tert-Butyloxazol-4-yl)methylene]-6-benzylpiperazine-2,5-dione

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Reaction Steps

Using a Dean-Stark trap whose trap part was filled with molecular sieves 3A, a solution of the compound from Example 7 (50 mg, 0.14 mmol) in toluene (20 mL) was refluxed in the presence of p-TsOH (0.8 mg, 0.0042 mmol) for 18 h. After removal of the solvent, the residue was purified by HPLC to obtain the title compound: yield 11.5 mg (23%), mp 52-56° C., 1H NMR (300 MHz, DMSO-d6) δ 10.65 (s, 1H), 8.60 (s, 1H), 8.47 (s, 1H), 7.24-7.13 (m, 5H), 6.37 (s, 1H), 4.52 (m, 1H), 3.20 (dd, J=3.7, 13.6 Hz, 1H), 2.95 (dd, J=5.0, 13.6 Hz, 1H), 1.31 (s, 9H); HRMS (EI): m/z 339.1584 (M+) (calcd for C19H21N3O3: 339.1583); [α]D25−128.9 (c=0.27, DMSO). Enantiomeric excess was determined to be 98% using chiral HPLC with a CHIRALCEL OD column.

Provenance & Evidence