p-Toluenesulfonic acid → L-leucine cyclopentyl ester tosylate

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To a suspension of (S)-leucine (15 g, 0.11 mol) in cyclohexane (400 ml) was added cyclopentanol (103.78 ml, 1.14 mmol) and p-toluene sulfonic acid (23.93 g, 0.13 mol). The suspension was heated at reflux to effect solvation. After refluxing the solution for 16 hours it was cooled to give a white suspension. Heptane (500 ml) was added to the mixture and the suspension was filtered to give the product as a white solid (35 g, 85% yield). 1H NMR (300 MHz, MeOD), δ: 1.01 (6H, t, CH3×2, J=5.8 Hz), 1.54-2.03 (11H, m, 11×CH), 2.39 (3H, s, CH3), 3.96 (1H, t, CH, J=6.5 Hz), 5.26-5.36 (1H, m, CH), 7.25 (2H, d, ArH×2, J=7.9 Hz), 7.72 (2H, d, ArH×2, J=8.3 Hz).

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