Hydrochloric Acid → 1-(tert-Butoxycarbonyl)-2-pyrroleboronic Acid

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A solution of anhydrous diisopropylamine (3.35 mL, 23.9 mmol) was prepared in 100 mL of anhydrous THF and cooled at −78° C. A solution of 2.5 M of n-butyllithium (10.5 mL, 26.3 mmol) was slowly added to the THF solution over 10 minutes. The resulting mixture was stirred at −78° C. for 15 minutes and was then warmed to 0° C. for 15 minutes. The resulting mixture was cooled again at −78° C. and the tert-butyl 1-pyrrole carboxylate (73) (4.00 mL, 23.9 mmol) was added. The resulting solution was stirred for 1 hour at −78° C. and trimethyl borate (2.70 mL, 23.9 mmol) was added. The resulting solution was allowed to warm up to room temperature overnight. 20 mL of dilute HCl (0.25N) was added to the room temperature solution, which was stirred at room temperature for 15 minutes. The THF was removed under reduced pressure. The residue was extracted with diethyl ether (3×100 mL). The organic layer was dried over sodium sulfate, filtered and then concentrated in vacuo. Trituration with hexane (10 mL) and filtration gave the Compound 8 as beige solid (2.56 g, 51%). 1H NMR (500 MHz, CDCl3): δ (ppm), 7.71 (s, 2H); 7.48 (t, 1H, J=2 Hz); 7.15 (t, 1H, J=1.8 Hz); 6.29 (t, 1H, J=3.1 Hz); 1.65 (3, 9H). 13C NMR (500 MHz, CDCl3): δ (ppm), 153.22; 129.67; 127.92; 112.96; 86.47; 28.84.

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