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 dimerization of α-amino acids: The amino acid (1 mmol) was suspended in 3 mL toluene together with few drops of 1,3-dimethylimidazolium dimethylphosphate. Triethylamine (4 mmol) and methyl dichlorophosphite (1 mmol) were added via canula. After irradiation under closed vessel microwave conditions at 145 °C for 1 h, the solution was filtered off an the precipitate was washed with hot toluene. The filtrate was evaporated and the resulting crude product was purified by flash column chromatography, if necessaryAnalysis of the target compound: 38 mg, 96% (Scale 0.2 mmol). – [α]D20= –4.02° (MeOH, c = 1.02). – 1H NMR (400 MHz, CDCl3): d = 2.08–2.16 (m, 2 H, 2 × CH2), 2.57 (dd, J = 13.8 Hz, 2 H, 2 × CH2), 3.28–3.42 (m, 2 H, CH2CH), 3.62 (dd, J = 13.4 Hz, J = 4.6 Hz, 2 H, 2 × NCH2), 3.68–3.80 (m, 2 H, 2 × NCH2), 4.15–4.32 (m, 2 H, 2 × CHOBn), 4.54 (s, 4 H, 2 × CH2Ph), 7.23–7.39 (m, 10 H, H-Ar). ). – 13C NMR (100 MHz, CDCl3): d = 33.8 (s, 2 C, CH2), 50.9 (s, 2 C, NCH2), 58.8 (p, 2 C, 2 × CH), 70.7 (p, 2 C, 2 × CHBn), 75.4 (s, 2 C, 2 × CH2Ph), 127.5 (t, 2 C, Ar-C), 127.8 (t, C-Ar), 128.4 (t, C-Ar), 137.2 (q, 2 C), 166.2 (q, 2 C, CO). – IR (neat): ν = 2942 (w), 2739 (w), 2678 (w), 2492 (m), 1669 (m), 1578 (w), 1454 (m), 1399 (w), 1362 (w), 1263 (m), 1201 (m), 1099 (m), 800 (w), 741 (w), 720 (w), 701 (w), 632 (w) cm-1. – EI–MS (70 eV): m/z (%): 406 (7) [M+], 315 (3), 300 (10), 90 (100). – HRMS (C24H26N2O4): calcd 406.1892, found 406.1896.
