The information given below was retrieved and reworked from the publication: Microwave-Assisted Stereoselective One-Pot Synthesis of Symmetrical and Unsymmetrical 2,5-Diketopiperazines from Unprotected Amino Acids by Manuel Jainta, Martin Nieger and Stefan Bräse. https://doi.org/10.1002/ejoc.200800605The reaction was conducted according to the general Procedure for the synthesis of cross-coupled 2,5-Diketopiperazines: The first amino acid (1 mmol) was suspended in 4 mL of toluene together with few drops of 1,3-dimethylimidazolium dimethylphosphate. Triethylamine (4 mmol), methyldichlorophosphite (1 mmol) and the second amino acid (1.2 mmol) were added subsequently. After irradiation under closed vessel microwave conditions at 145 °C for 1 h, the solution was filtered off and the precipitate was washed with hot toluene. The filtrate was evaporated and the resulting crude product was purified by flash column chromatography, if necessary.Analysis of the target compound: 121 mg, 93% (Scale 0.6 mmol). – Rf = 0.48 (Hexane/EE 3:1). – [α]D20= –6.44° (CHCl3, c = 0.51). – Mp: 248–252 °C. – 1H NMR (400 MHz, CDCl3): d = 3.07 (s, 3 H, CH3), 3.44 (dd, Jgem = 16.8 Hz, J = 10.3 Hz, 1 H, 10-H), 3.79 (dd, Jgem = 16.8 Hz, J = 9.0 Hz, 1 H, 10-H), 3.88–3.98 (m, 1 H, 3-H), 4.30–4.41 (m, 1 H, 3-H), 4.97 (dd, J = 10.3 Hz, J = 9.0 Hz, 1 H, 10a-H), 7.07–7.14 (m, 1 H, Ar-H), 7.21–7.30 (m, 2 H, Ar-H), 8.02–8.12 (m, 1 H, Ar-H). – 13C NMR (100 MHz, CDCl3): d = 30.1 (p, CH3), 33.8 (s, C-10), 54.2 (s, C-3), 61.6 (t, C-10a), 115.7 (t, C-6), 125.0 (t, C-8), 127.9 (t, C-7), 129.7 (t, C-9), 140.4 (q, C-9a), 140.7 (q, C-5a), 164.2 (q, C-4), 166.9 (q, C-1). – IR (neat): n = 3344 (w), 3051 (m), 2898 (m), 2863 (w), 1681 (s), 1603 (m), 1483 (s), 1462 (m), 1410 (m), 1343 (m), 1315 (m), 1246 (m), 1213 (m), 1183 (w), 1155 (w), 1132 (m), 1086 (m), 1058 (w), 1018 (m), 996 (m), 930 (w), 867 (w), 849 (w), 777 (m), 755 (m), 712 (w), 647 (w), 599 (w), 564 (w), 528 (m), 421 (m) cm-1. – EI–MS (70 eV): m/z (%): 216 (100) [M+], 199 (12), 142 (27), 131 (12), 117 (40), 90 (10). – HRMS (C12H12N2O2): calcd 216.0899, found 216.0896.
