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0 °C

To a solution of 1.20 g of 3,3-dimethyl-6-nitrobenzo[c][1,2]oxaborol-1(3H)-ol (XCVII) (1.20 g, 5.8 mmol) in MeOH (30 mL) was added 3M aqueous HCl (30 mL), and the mixture was cooled to 0° C. To this mixture was added portion-wise zinc dust (3.77 g, 0.058 mol), maintaining the temperature below 5° C. The mixture was stirred for 40 min at room temperature. A gray solid was removed by filtration through a Celite pad. The filtrate was concentrated in vacuo and the residue was dissolved in EtOAc and stirred. 1M aqueous K2CO3 was added to pH=7 and stirring was continued for 10 min. The two phases were separated and the aqueous layer was extracted with EtOAc. The combined organic phases were dried over MgSO4 filtered and concentrated in vacuo. The crude product was purified by silica gel chromatography using DCM then DCM/MeOH 500/1→300/1→200/1→100/1 to give 6-amino-3,3-dimethylbenzo[c][1,2]oxaborol-1(3H)-ol (XCVIII) as an orange solid (0.62 g, 3.5 mmol, yield 60%). 1H NMR (DMSO-d6) δ ppm 1.46 (s, 6H), 7.43 (dd, J=8 Hz, J=2 Hz, 1H), 7.55 (d. J=8 Hz, 1H), 7.67 (d, J=2 Hz, 1H), 9.95-10.72 (brs, 3H) ESIMS found for C9H12BNO2 m/z 178.1 (M+H).

1. temperaturemaintaining the temperature below 5° C
2. customA gray solid was removed by filtration through a Celite pad
3. concentrationThe filtrate was concentrated in vacuo
4. dissolutionthe residue was dissolved in EtOAc
5. stirringstirred
6. addition1M aqueous K2CO3 was added to pH=7
7. stirringstirring
8. waitwas continued for 10 min
9. customThe two phases were separated
10. extractionthe aqueous layer was extracted with EtOAc
11. dry with materialThe combined organic phases were dried over MgSO4
12. filtrationfiltered
13. concentrationconcentrated in vacuo
14. customThe crude product was purified by silica gel chromatography