Sodium Bicarbonate → (S)-ethyl 2-(2-bromo-7-(4-chlorophenyl)-5-methylbenzo[d]thiazol-6-yl)-2-tert-butoxyacetate

Participants

Reaction Conditions

Reaction Steps

A suspension of (S)-ethyl 2-(2-bromo-7-(4-chlorophenyl)-5-methylbenzo[d]thiazol-6-yl)-2-hydroxyacetate (7.20 g, 16.9 mmol) in neat t-BuOAc (100 mL) was cooled to 0° C. in an ice bath. 70% w/v aqueous HClO4 (293 μL, 3.4 mmol) was added dropwise over 5 min. The reaction was warmed to 23° C., then stirred for 2.3 h. At this point the reaction was transferred to an addition funnel. The reaction was added to a 23° C. solution of sat aqueous NaHCO3 (400 mL) over 30 min. Once addition was complete, the reaction was stirred for another 15 min. The resulting system was extracted with EtOAc (2×150 mL). Combined organic layers were dried (Na2SO4), filtered, and concentrated in vacuo. Some residual t-BuOAc remained. Hexane (200 mL) was added and the slurry was concentrated once more. The resulting residue (reasonably free of t-BuOAc) was treated with Benzene and loaded onto a 330 g “gold” ISCO silica gel column. The following gradient elution sequence was used: [100% Hexane (5 column volumes, isocratic)→10% EtOAc/90% Hexane (5 column volumes, linear gradient→10% EtOAc/90% Hexane (5 column volumes, isocratic ((S)-ethyl 2-(2-bromo-7-(4-chlorophenyl)-5-methylbenzo[d]thiazol-6-yl)-2-tert-butoxyacetate elutes))→100% EtOAc (10 column volumes, isocratic, (unreacted (S)-ethyl 2-(2-bromo-7-(4-chlorophenyl)-5-methylbenzo[d]thiazol-6-yl)-2-hydroxyacetate elutes))]. Product-containing fractions were pooled, concentrated, co-evarporated with Et2O (100 mL) to give desired product. LCMS-ESI+ calc'd for C22H23BrClNO3S: 496.0, 498.0 and 500.0 (M+H+); found: 496.2, 498.2, and 500.1 (M+H+). 1H NMR (400 MHz, CDCl3): δ 7.77 (s, 1H), 7.48 (m, 3H), 7.37 (m, 1H), 5.12 (s, 1H), 4.20 (m, 2H), 2.57 (s, 3H), 1.24 (t, 3H, J=7 Hz), 0.96 (s, 9H).

Provenance & Evidence