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5. After chromatography of the crude reaction (eluting with hexane/ethyl acetate) in addition to the 1,3-diiodopropane the byproduct 7 was isolated in about 10% yield, while the separation of diastereomers of 2 was unsuccessful. However, the subsequent cyclization reaction6 leads to easily separable diastereomers 3 and 4. The structure of 7 was determined by 1H NMR spectroscopic data and further corroborated by smooth conversion into 6 with refluxing 57% HI. (1′S,2S)-1,3-Bis-[1,4-N,N-(1′-phenethyl)-3,6-diketopiperazin-2-yl]-propane 7: 1H NMR δ (CDCl3) 1.5 (d, 6H, J=7.2 Hz), 1.6 (d, 6H, J=7.2 Hz), 1.6 (m, 2H), 1.85 (m, 4H), 3.56 (d, 2H, J=17.4 Hz), 3.68 (dd, 2H, J=4.5, 8.4 Hz), 3.94 (d, 2H, J=17.4 Hz), 5.78 (q, 2H, J=7.2 Hz), 5.8 (q, 2H, J=7.2 Hz), 7.3 (m, 20ArH); 13C NMR δ (CDCl3) 15.2, 17.3, 21, 33.1, 44.4, 49.7, 51.8, 56.8, 126.8, 127.8, 127.9, 128.6, 128.7, 138.5, 138.9, 165, 165.9; [α]D −176.1 (c 1.01, CHCl3).