(R)-2-Methyl-CBS-oxazaborolidine → (S)-ethyl 2-(2-bromo-5-methyl-7-(trifluoromethylsulfonyloxy)benzo[d]thiazol-6-yl)-2-hydroxyacetate

To a solution of 30 (8.30 g, 17.4 mmol) in toluene (70 mL) was added ((R)-2-methyl-CBS-oxazaborolidine (725 mg, 2.61 mmol). The reaction mixture was then cooled to −35° C. and a solution of catecholborane (freshly distilled) (1 M in toluene, 20.9 mL, 20.9 mmol) was added via addition funnel over 30 min. The reaction was stirred for 20 min while warming to −20° C. A 2 M solution of Na2CO3 was added (50 mL). The layers were separated, and the organic layer was washed with additional Na2CO3 solution (3×25 mL). The organic layer was dried, filtered, and concentrated in vacuo to give 31, which had analytical data to match 29. The compound was taken on to the next step without further purification.