To a solution of benzyl 4-mercapto-2-methylbutan-2-ylcarbamate (20 mmol) in N,N-dimethylformamide (20 ml) was added cesium carbonate (6.49 g, 19.9 mmol) and 13-bromo-2,5,8,11-tetraoxatridecane (5.00 g, 18.4 mmol). The solution was stirred for 16 hours, concentrated in vacuo, and the residue dissolved in 500 ml ethylacetate, washed with 3 times with 100 ml 5% NaHSO4, 1×200 ml sat. NaCl, dried on MgSO4, and concentrated in vacuo. The residue was purified by flash chromatography (10% to 60% ethylacetate in hexanes) to give the titled compound as a clear oil (7.47 g, 18.1 mmol, 98%). 1H NMR (400 MHz, CDCl3) δ 1.31 (s, 6H), 1.95-1.99 (m, 2H), 2.51-2.55 (m, 2H), 2.69-2.73 (m, 2H), 3.38 (s, 3H), 3.54-3.58 (m, 2H, 3.6-3.7 (m, 14H), 4.77 (br s, 1H), 5.06 (s, 2H), 7.3-7.4 (m, 5H). LRMS (ESI/APCI): 466 [M+Na]+.
