To a round bottom flask equipped with a magnetic stirrer and nitrogen were added toluene-4-thiosulfonic acid S-(2-tert-butyl-4-hydroxy-5-methyl-phenyl) ester (prepared in Example RRR; 6.86 g, 19.6 mmol), Et2O (100 mL), and NEt3 (3.25 mL, 23.4 mmol), respectively. The solution was cooled to 0° C. and treated rapidly with a solution of (ethyl amino)sulfonyl chloride (3.37 g, 23.4 mmol) in Et2O (10 mL). The reaction was stirred for 30 minutes and then filtered. The solids were washed with Et2O, and the filtrate was concentrated. The resulting residue was dried in a high vacuum oven at 40° C. overnight to yield the title compound. 1H NMR (CDCl3) δ 1.15 (s, 9 H), 1.23 (t, 3 H) 2.19 (s, 3 H), 2.35 (s, 3 H), 3.30 (m, 2 H), 4.75 (br t, 1 H), 7.16 (s, 1 H), 7.19 (s, 1 H), 7.32 (d, 2 H), 7.39 (d, 2 H).
